- Assertion Testing
- Buffer
- C/C++ Addons
- Child Processes
- Cluster
- Command Line Options
- Console
- Crypto
- Debugger
- DNS
- Domain
- Errors
- Events
- File System
- Globals
- HTTP
- HTTPS
- Internationalization
- Modules
- Net
- OS
- Path
- Process
- Punycode
- Query Strings
- Readline
- REPL
- Stream
- String Decoder
- Timers
- TLS/SSL
- TTY
- UDP/Datagram
- URL
- Utilities
- V8
- VM
- ZLIB
Node.js v6.13.2-test20180313acaeb8f006 Documentation
Table of Contents
- About this Documentation
- Usage
- C/C++ Addons
- Assert
- assert(value[, message])
- assert.deepEqual(actual, expected[, message])
- assert.deepStrictEqual(actual, expected[, message])
- assert.doesNotThrow(block[, error][, message])
- assert.equal(actual, expected[, message])
- assert.fail(message)
- assert.fail(actual, expected[, message[, operator[, stackStartFunction]]])
- assert.ifError(value)
- assert.notDeepEqual(actual, expected[, message])
- assert.notDeepStrictEqual(actual, expected[, message])
- assert.notEqual(actual, expected[, message])
- assert.notStrictEqual(actual, expected[, message])
- assert.ok(value[, message])
- assert.strictEqual(actual, expected[, message])
- assert.throws(block[, error][, message])
- Buffer
Buffer.from()
,Buffer.alloc()
, andBuffer.allocUnsafe()
- Buffers and Character Encodings
- Buffers and TypedArray
- Buffers and ES6 iteration
- Class: Buffer
- new Buffer(array)
- new Buffer(buffer)
- new Buffer(arrayBuffer[, byteOffset [, length]])
- new Buffer(size)
- new Buffer(string[, encoding])
- Class Method: Buffer.alloc(size[, fill[, encoding]])
- Class Method: Buffer.allocUnsafe(size)
- Class Method: Buffer.allocUnsafeSlow(size)
- Class Method: Buffer.byteLength(string[, encoding])
- Class Method: Buffer.compare(buf1, buf2)
- Class Method: Buffer.concat(list[, totalLength])
- Class Method: Buffer.from(array)
- Class Method: Buffer.from(arrayBuffer[, byteOffset[, length]])
- Class Method: Buffer.from(buffer)
- Class Method: Buffer.from(string[, encoding])
- Class Method: Buffer.isBuffer(obj)
- Class Method: Buffer.isEncoding(encoding)
- Class Property: Buffer.poolSize
- buf[index]
- buf.compare(target[, targetStart[, targetEnd[, sourceStart[, sourceEnd]]]])
- buf.copy(target[, targetStart[, sourceStart[, sourceEnd]]])
- buf.entries()
- buf.equals(otherBuffer)
- buf.fill(value[, offset[, end]][, encoding])
- buf.includes(value[, byteOffset][, encoding])
- buf.indexOf(value[, byteOffset][, encoding])
- buf.includes(value[, byteOffset][, encoding])
- buf.keys()
- buf.lastIndexOf(value[, byteOffset][, encoding])
- buf.length
- buf.readDoubleBE(offset[, noAssert])
- buf.readDoubleLE(offset[, noAssert])
- buf.readFloatBE(offset[, noAssert])
- buf.readFloatLE(offset[, noAssert])
- buf.readInt8(offset[, noAssert])
- buf.readInt16BE(offset[, noAssert])
- buf.readInt16LE(offset[, noAssert])
- buf.readInt32BE(offset[, noAssert])
- buf.readInt32LE(offset[, noAssert])
- buf.readIntBE(offset, byteLength[, noAssert])
- buf.readIntLE(offset, byteLength[, noAssert])
- buf.readUInt8(offset[, noAssert])
- buf.readUInt16BE(offset[, noAssert])
- buf.readUInt16LE(offset[, noAssert])
- buf.readUInt32BE(offset[, noAssert])
- buf.readUInt32LE(offset[, noAssert])
- buf.readUIntBE(offset, byteLength[, noAssert])
- buf.readUIntLE(offset, byteLength[, noAssert])
- buf.slice([start[, end]])
- buf.swap16()
- buf.swap32()
- buf.swap64()
- buf.toString([encoding[, start[, end]]])
- buf.toJSON()
- buf.values()
- buf.write(string[, offset[, length]][, encoding])
- buf.writeDoubleBE(value, offset[, noAssert])
- buf.writeDoubleLE(value, offset[, noAssert])
- buf.writeFloatBE(value, offset[, noAssert])
- buf.writeFloatLE(value, offset[, noAssert])
- buf.writeInt8(value, offset[, noAssert])
- buf.writeInt16BE(value, offset[, noAssert])
- buf.writeInt16LE(value, offset[, noAssert])
- buf.writeInt32BE(value, offset[, noAssert])
- buf.writeInt32LE(value, offset[, noAssert])
- buf.writeIntBE(value, offset, byteLength[, noAssert])
- buf.writeIntLE(value, offset, byteLength[, noAssert])
- buf.writeUInt8(value, offset[, noAssert])
- buf.writeUInt16BE(value, offset[, noAssert])
- buf.writeUInt16LE(value, offset[, noAssert])
- buf.writeUInt32BE(value, offset[, noAssert])
- buf.writeUInt32LE(value, offset[, noAssert])
- buf.writeUIntBE(value, offset, byteLength[, noAssert])
- buf.writeUIntLE(value, offset, byteLength[, noAssert])
- buffer.INSPECT_MAX_BYTES
- buffer.kMaxLength
- Class: SlowBuffer
- Child Process
- Asynchronous Process Creation
- Synchronous Process Creation
- Class: ChildProcess
- Event: 'close'
- Event: 'disconnect'
- Event: 'error'
- Event: 'exit'
- Event: 'message'
- subprocess.connected
- subprocess.disconnect()
- subprocess.kill([signal])
- subprocess.killed
- subprocess.pid
- subprocess.send(message[, sendHandle[, options]][, callback])
- subprocess.stderr
- subprocess.stdin
- subprocess.stdio
- subprocess.stdout
maxBuffer
and Unicode
- Cluster
- How It Works
- Class: Worker
- Event: 'disconnect'
- Event: 'error'
- Event: 'exit'
- Event: 'listening'
- Event: 'message'
- Event: 'online'
- worker.disconnect()
- worker.exitedAfterDisconnect
- worker.id
- worker.isConnected()
- worker.isDead()
- worker.kill([signal='SIGTERM'])
- worker.process
- worker.send(message[, sendHandle][, callback])
- worker.suicide
- Event: 'disconnect'
- Event: 'exit'
- Event: 'fork'
- Event: 'listening'
- Event: 'message'
- Event: 'online'
- Event: 'setup'
- cluster.disconnect([callback])
- cluster.fork([env])
- cluster.isMaster
- cluster.isWorker
- cluster.schedulingPolicy
- cluster.settings
- cluster.setupMaster([settings])
- cluster.worker
- cluster.workers
- Command Line Options
- Synopsis
- Options
-v
,--version
-h
,--help
-e
,--eval "script"
-p
,--print "script"
-c
,--check
-i
,--interactive
-r
,--require module
--no-deprecation
--trace-deprecation
--throw-deprecation
--no-warnings
--trace-warnings
--redirect-warnings=file
--trace-sync-io
--zero-fill-buffers
--preserve-symlinks
--track-heap-objects
--prof-process
--v8-options
--tls-cipher-list=list
--enable-fips
--force-fips
--openssl-config=file
--use-openssl-ca
,--use-bundled-ca
--icu-data-dir=file
--
- Environment Variables
- Console
- Class: Console
- new Console(stdout[, stderr])
- console.assert(value[, message][, ...args])
- console.clear()
- console.count([label])
- console.countReset([label = 'default'])
- console.dir(obj[, options])
- console.error([data][, ...args])
- console.info([data][, ...args])
- console.log([data][, ...args])
- console.time(label)
- console.timeEnd(label)
- console.trace(message[, ...args])
- console.warn([data][, ...args])
- Class: Console
- Crypto
- Determining if crypto support is unavailable
- Class: Certificate
- Class: Cipher
- Class: Decipher
- Class: DiffieHellman
- diffieHellman.computeSecret(other_public_key[, input_encoding][, output_encoding])
- diffieHellman.generateKeys([encoding])
- diffieHellman.getGenerator([encoding])
- diffieHellman.getPrime([encoding])
- diffieHellman.getPrivateKey([encoding])
- diffieHellman.getPublicKey([encoding])
- diffieHellman.setPrivateKey(private_key[, encoding])
- diffieHellman.setPublicKey(public_key[, encoding])
- diffieHellman.verifyError
- Class: ECDH
- Class: Hash
- Class: Hmac
- Class: Sign
- Class: Verify
crypto
module methods and properties- crypto.constants
- crypto.DEFAULT_ENCODING
- crypto.fips
- crypto.createCipher(algorithm, password)
- crypto.createCipheriv(algorithm, key, iv)
- crypto.createCredentials(details)
- crypto.createDecipher(algorithm, password)
- crypto.createDecipheriv(algorithm, key, iv)
- crypto.createDiffieHellman(prime[, prime_encoding][, generator][, generator_encoding])
- crypto.createDiffieHellman(prime_length[, generator])
- crypto.createECDH(curve_name)
- crypto.createHash(algorithm)
- crypto.createHmac(algorithm, key)
- crypto.createSign(algorithm)
- crypto.createVerify(algorithm)
- crypto.getCiphers()
- crypto.getCurves()
- crypto.getDiffieHellman(group_name)
- crypto.getHashes()
- crypto.pbkdf2(password, salt, iterations, keylen, digest, callback)
- crypto.pbkdf2Sync(password, salt, iterations, keylen, digest)
- crypto.privateDecrypt(private_key, buffer)
- crypto.timingSafeEqual(a, b)
- crypto.privateEncrypt(private_key, buffer)
- crypto.publicDecrypt(public_key, buffer)
- crypto.publicEncrypt(public_key, buffer)
- crypto.randomBytes(size[, callback])
- crypto.randomFillSync(buffer[, offset][, size])
- crypto.randomFill(buffer[, offset][, size], callback)
- crypto.setEngine(engine[, flags])
- Notes
- Crypto Constants
- Debugger
- UDP / Datagram Sockets
- Class: dgram.Socket
- Event: 'close'
- Event: 'error'
- Event: 'listening'
- Event: 'message'
- socket.addMembership(multicastAddress[, multicastInterface])
- socket.address()
- socket.bind([port][, address][, callback])
- socket.bind(options[, callback])
- socket.close([callback])
- socket.dropMembership(multicastAddress[, multicastInterface])
- socket.send(msg, [offset, length,] port, address[, callback])
- socket.setBroadcast(flag)
- socket.setMulticastInterface(multicastInterface)
- socket.setMulticastLoopback(flag)
- socket.setMulticastTTL(ttl)
- socket.setTTL(ttl)
- socket.ref()
- socket.unref()
- Change to asynchronous
socket.bind()
behavior
dgram
module functions
- Class: dgram.Socket
- DNS
- dns.getServers()
- dns.lookup(hostname[, options], callback)
- dns.lookupService(address, port, callback)
- dns.resolve(hostname[, rrtype], callback)
- dns.resolve4(hostname[, options], callback)
- dns.resolve6(hostname[, options], callback)
- dns.resolveCname(hostname, callback)
- dns.resolveMx(hostname, callback)
- dns.resolveNaptr(hostname, callback)
- dns.resolveNs(hostname, callback)
- dns.resolveSoa(hostname, callback)
- dns.resolveSrv(hostname, callback)
- dns.resolvePtr(hostname, callback)
- dns.resolveTxt(hostname, callback)
- dns.reverse(ip, callback)
- dns.setServers(servers)
- Error codes
- Implementation considerations
- Domain
- Errors
- Events
- Passing arguments and
this
to listeners - Asynchronous vs. Synchronous
- Handling events only once
- Error events
- Class: EventEmitter
- Event: 'newListener'
- Event: 'removeListener'
- EventEmitter.listenerCount(emitter, eventName)
- EventEmitter.defaultMaxListeners
- emitter.addListener(eventName, listener)
- emitter.emit(eventName[, ...args])
- emitter.eventNames()
- emitter.getMaxListeners()
- emitter.listenerCount(eventName)
- emitter.listeners(eventName)
- emitter.on(eventName, listener)
- emitter.once(eventName, listener)
- emitter.prependListener(eventName, listener)
- emitter.prependOnceListener(eventName, listener)
- emitter.removeAllListeners([eventName])
- emitter.removeListener(eventName, listener)
- emitter.setMaxListeners(n)
- Passing arguments and
- File System
- Buffer API
- Class: fs.FSWatcher
- Class: fs.ReadStream
- Class: fs.Stats
- Class: fs.WriteStream
- fs.access(path[, mode], callback)
- fs.accessSync(path[, mode])
- fs.appendFile(file, data[, options], callback)
- fs.appendFileSync(file, data[, options])
- fs.chmod(path, mode, callback)
- fs.chmodSync(path, mode)
- fs.chown(path, uid, gid, callback)
- fs.chownSync(path, uid, gid)
- fs.close(fd, callback)
- fs.closeSync(fd)
- fs.constants
- fs.createReadStream(path[, options])
- fs.createWriteStream(path[, options])
- fs.exists(path, callback)
- fs.existsSync(path)
- fs.fchmod(fd, mode, callback)
- fs.fchmodSync(fd, mode)
- fs.fchown(fd, uid, gid, callback)
- fs.fchownSync(fd, uid, gid)
- fs.fdatasync(fd, callback)
- fs.fdatasyncSync(fd)
- fs.fstat(fd, callback)
- fs.fstatSync(fd)
- fs.fsync(fd, callback)
- fs.fsyncSync(fd)
- fs.ftruncate(fd, len, callback)
- fs.ftruncateSync(fd, len)
- fs.futimes(fd, atime, mtime, callback)
- fs.futimesSync(fd, atime, mtime)
- fs.lchmod(path, mode, callback)
- fs.lchmodSync(path, mode)
- fs.lchown(path, uid, gid, callback)
- fs.lchownSync(path, uid, gid)
- fs.link(existingPath, newPath, callback)
- fs.linkSync(existingPath, newPath)
- fs.lstat(path, callback)
- fs.lstatSync(path)
- fs.mkdir(path[, mode], callback)
- fs.mkdirSync(path[, mode])
- fs.mkdtemp(prefix[, options], callback)
- fs.mkdtempSync(prefix[, options])
- fs.open(path, flags[, mode], callback)
- fs.openSync(path, flags[, mode])
- fs.read(fd, buffer, offset, length, position, callback)
- fs.readdir(path[, options], callback)
- fs.readdirSync(path[, options])
- fs.readFile(file[, options], callback)
- fs.readFileSync(file[, options])
- fs.readlink(path[, options], callback)
- fs.readlinkSync(path[, options])
- fs.readSync(fd, buffer, offset, length, position)
- fs.realpath(path[, options], callback)
- fs.realpathSync(path[, options])
- fs.rename(oldPath, newPath, callback)
- fs.renameSync(oldPath, newPath)
- fs.rmdir(path, callback)
- fs.rmdirSync(path)
- fs.stat(path, callback)
- fs.statSync(path)
- fs.symlink(target, path[, type], callback)
- fs.symlinkSync(target, path[, type])
- fs.truncate(path, len, callback)
- fs.truncateSync(path, len)
- fs.unlink(path, callback)
- fs.unlinkSync(path)
- fs.unwatchFile(filename[, listener])
- fs.utimes(path, atime, mtime, callback)
- fs.utimesSync(path, atime, mtime)
- fs.watch(filename[, options][, listener])
- fs.watchFile(filename[, options], listener)
- fs.write(fd, buffer[, offset[, length[, position]]], callback)
- fs.write(fd, string[, position[, encoding]], callback)
- fs.writeFile(file, data[, options], callback)
- fs.writeFileSync(file, data[, options])
- fs.writeSync(fd, buffer[, offset[, length[, position]]])
- fs.writeSync(fd, string[, position[, encoding]])
- FS Constants
- Global Objects
- HTTP
- Class: http.Agent
- Class: http.ClientRequest
- Event: 'abort'
- Event: 'connect'
- Event: 'continue'
- Event: 'response'
- Event: 'socket'
- Event: 'upgrade'
- request.abort()
- request.aborted
- request.end([data][, encoding][, callback])
- request.flushHeaders()
- request.setNoDelay([noDelay])
- request.setSocketKeepAlive([enable][, initialDelay])
- request.setTimeout(timeout[, callback])
- request.write(chunk[, encoding][, callback])
- Class: http.Server
- Event: 'checkContinue'
- Event: 'checkExpectation'
- Event: 'clientError'
- Event: 'close'
- Event: 'connect'
- Event: 'connection'
- Event: 'request'
- Event: 'upgrade'
- server.close([callback])
- server.listen(handle[, callback])
- server.listen(path[, callback])
- server.listen([port][, hostname][, backlog][, callback])
- server.listening
- server.maxHeadersCount
- server.setTimeout(msecs, callback)
- server.timeout
- Class: http.ServerResponse
- Event: 'close'
- Event: 'finish'
- response.addTrailers(headers)
- response.end([data][, encoding][, callback])
- response.finished
- response.getHeader(name)
- response.headersSent
- response.removeHeader(name)
- response.sendDate
- response.setHeader(name, value)
- response.setTimeout(msecs, callback)
- response.statusCode
- response.statusMessage
- response.write(chunk[, encoding][, callback])
- response.writeContinue()
- response.writeHead(statusCode[, statusMessage][, headers])
- Class: http.IncomingMessage
- http.METHODS
- http.STATUS_CODES
- http.createClient([port][, host])
- http.createServer([requestListener])
- http.get(options[, callback])
- http.globalAgent
- http.request(options[, callback])
- HTTPS
- Internationalization Support
- Modules
- Net
- Class: net.Server
- Event: 'close'
- Event: 'connection'
- Event: 'error'
- Event: 'listening'
- server.address()
- server.close([callback])
- server.connections
- server.getConnections(callback)
- server.listen(handle[, backlog][, callback])
- server.listen(options[, callback])
- server.listen(path[, backlog][, callback])
- server.listen([port][, hostname][, backlog][, callback])
- server.listening
- server.maxConnections
- server.ref()
- server.unref()
- Class: net.Socket
- new net.Socket([options])
- Event: 'close'
- Event: 'connect'
- Event: 'data'
- Event: 'drain'
- Event: 'end'
- Event: 'error'
- Event: 'lookup'
- Event: 'timeout'
- socket.address()
- socket.bufferSize
- socket.bytesRead
- socket.bytesWritten
- socket.connect(options[, connectListener])
- socket.connect(path[, connectListener])
- socket.connect(port[, host][, connectListener])
- socket.connecting
- socket.destroy([exception])
- socket.destroyed
- socket.end([data][, encoding])
- socket.localAddress
- socket.localPort
- socket.pause()
- socket.ref()
- socket.remoteAddress
- socket.remoteFamily
- socket.remotePort
- socket.resume()
- socket.setEncoding([encoding])
- socket.setKeepAlive([enable][, initialDelay])
- socket.setNoDelay([noDelay])
- socket.setTimeout(timeout[, callback])
- socket.unref()
- socket.write(data[, encoding][, callback])
- net.connect(options[, connectListener])
- net.connect(path[, connectListener])
- net.connect(port[, host][, connectListener])
- net.createConnection(options[, connectListener])
- net.createConnection(path[, connectListener])
- net.createConnection(port[, host][, connectListener])
- net.createServer([options][, connectionListener])
- net.isIP(input)
- net.isIPv4(input)
- net.isIPv6(input)
- Class: net.Server
- OS
- Path
- Process
- Process Events
- process.abort()
- process.arch
- process.argv
- process.argv0
- process.chdir(directory)
- process.config
- process.connected
- process.cpuUsage([previousValue])
- process.cwd()
- process.disconnect()
- process.env
- process.emitWarning(warning[, name][, ctor])
- process.execArgv
- process.execPath
- process.exit([code])
- process.exitCode
- process.getegid()
- process.geteuid()
- process.getgid()
- process.getgroups()
- process.getuid()
- process.hrtime([time])
- process.initgroups(user, extra_group)
- process.kill(pid[, signal])
- process.mainModule
- process.memoryUsage()
- process.nextTick(callback[, ...args])
- process.noDeprecation
- process.pid
- process.platform
- process.ppid
- process.release
- process.send(message[, sendHandle[, options]][, callback])
- process.setegid(id)
- process.seteuid(id)
- process.setgid(id)
- process.setgroups(groups)
- process.setuid(id)
- process.stderr
- process.stdin
- process.stdout
- process.throwDeprecation
- process.title
- process.traceDeprecation
- process.umask([mask])
- process.uptime()
- process.version
- process.versions
- Exit Codes
- Punycode
- Query String
- Readline
- REPL
- Stream
- Organization of this Document
- Types of Streams
- API for Stream Consumers
- API for Stream Implementers
- Additional Notes
- String Decoder
- Timers
- TLS (SSL)
- TLS/SSL Concepts
- Modifying the Default TLS Cipher suite
- Class: tls.Server
- Event: 'tlsClientError'
- Event: 'newSession'
- Event: 'OCSPRequest'
- Event: 'resumeSession'
- Event: 'secureConnection'
- server.addContext(hostname, context)
- server.address()
- server.close([callback])
- server.connections
- server.getTicketKeys()
- server.listen(port[, hostname][, callback])
- server.setTicketKeys(keys)
- Class: tls.TLSSocket
- new tls.TLSSocket(socket[, options])
- Event: 'OCSPResponse'
- Event: 'secureConnect'
- tlsSocket.address()
- tlsSocket.authorized
- tlsSocket.authorizationError
- tlsSocket.encrypted
- tlsSocket.getCipher()
- tlsSocket.getEphemeralKeyInfo()
- tlsSocket.getPeerCertificate([ detailed ])
- tlsSocket.getProtocol()
- tlsSocket.getSession()
- tlsSocket.getTLSTicket()
- tlsSocket.localAddress
- tlsSocket.localPort
- tlsSocket.remoteAddress
- tlsSocket.remoteFamily
- tlsSocket.remotePort
- tlsSocket.renegotiate(options, callback)
- tlsSocket.setMaxSendFragment(size)
- tls.connect(port[, host][, options][, callback])
- tls.connect(path[, options][, callback])
- tls.connect(options[, callback])
- tls.createSecureContext(options)
- tls.createServer([options][, secureConnectionListener])
- tls.getCiphers()
- tls.DEFAULT_ECDH_CURVE
- Deprecated APIs
- TTY
- URL
- URL Strings and URL Objects
- The WHATWG URL API
- Class: URL
- Class: URLSearchParams
- Constructor: new URLSearchParams()
- Constructor: new URLSearchParams(string)
- Constructor: new URLSearchParams(obj)
- Constructor: new URLSearchParams(iterable)
- urlSearchParams.append(name, value)
- urlSearchParams.delete(name)
- urlSearchParams.entries()
- urlSearchParams.forEach(fn[, thisArg])
- urlSearchParams.get(name)
- urlSearchParams.getAll(name)
- urlSearchParams.has(name)
- urlSearchParams.keys()
- urlSearchParams.set(name, value)
- urlSearchParams.sort()
- urlSearchParams.toString()
- urlSearchParams.values()
- urlSearchParams[@@iterator]()
- url.domainToASCII(domain)
- url.domainToUnicode(domain)
- Legacy URL API
- Percent-Encoding in URLs
- Util
- util.debuglog(section)
- util.deprecate(function, string)
- util.format(format[, ...args])
- util.inherits(constructor, superConstructor)
- util.inspect(object[, options])
- Deprecated APIs
- util.debug(string)
- util.error([...strings])
- util.isArray(object)
- util.isBoolean(object)
- util.isBuffer(object)
- util.isDate(object)
- util.isError(object)
- util.isFunction(object)
- util.isNull(object)
- util.isNullOrUndefined(object)
- util.isNumber(object)
- util.isObject(object)
- util.isPrimitive(object)
- util.isRegExp(object)
- util.isString(object)
- util.isSymbol(object)
- util.isUndefined(object)
- util.log(string)
- util.print([...strings])
- util.puts([...strings])
- util._extend(target, source)
- V8
- VM (Executing JavaScript)
- Class: vm.Script
- vm.createContext([sandbox])
- vm.isContext(sandbox)
- vm.runInContext(code, contextifiedSandbox[, options])
- vm.runInDebugContext(code)
- vm.runInNewContext(code[, sandbox][, options])
- vm.runInThisContext(code[, options])
- Example: Running an HTTP Server within a VM
- What does it mean to "contextify" an object?
- Zlib
- Compressing HTTP requests and responses
- Memory Usage Tuning
- Flushing
- Constants
- Class Options
- Class: zlib.Deflate
- Class: zlib.DeflateRaw
- Class: zlib.Gunzip
- Class: zlib.Gzip
- Class: zlib.Inflate
- Class: zlib.InflateRaw
- Class: zlib.Unzip
- Class: zlib.Zlib
- zlib.constants
- zlib.createDeflate([options])
- zlib.createDeflateRaw([options])
- zlib.createGunzip([options])
- zlib.createGzip([options])
- zlib.createInflate([options])
- zlib.createInflateRaw([options])
- zlib.createUnzip([options])
- Convenience Methods
- zlib.deflate(buf[, options], callback)
- zlib.deflateSync(buf[, options])
- zlib.deflateRaw(buf[, options], callback)
- zlib.deflateRawSync(buf[, options])
- zlib.gunzip(buf[, options], callback)
- zlib.gunzipSync(buf[, options])
- zlib.gzip(buf[, options], callback)
- zlib.gzipSync(buf[, options])
- zlib.inflate(buf[, options], callback)
- zlib.inflateSync(buf[, options])
- zlib.inflateRaw(buf[, options], callback)
- zlib.inflateRawSync(buf[, options])
- zlib.unzip(buf[, options], callback)
- zlib.unzipSync(buf[, options])
About this Documentation#
The goal of this documentation is to comprehensively explain the Node.js API, both from a reference as well as a conceptual point of view. Each section describes a built-in module or high-level concept.
Where appropriate, property types, method arguments, and the arguments provided to event handlers are detailed in a list underneath the topic heading.
Contributing#
If you find an error in this documentation, please submit an issue or see the contributing guide for directions on how to submit a patch.
Every file is generated based on the corresponding .md
file in the
doc/api/
folder in Node.js's source tree. The documentation is generated
using the tools/doc/generate.js
program. An HTML template is located at
doc/template.html
.
Stability Index#
Throughout the documentation, you will see indications of a section's stability. The Node.js API is still somewhat changing, and as it matures, certain parts are more reliable than others. Some are so proven, and so relied upon, that they are unlikely to ever change at all. Others are brand new and experimental, or known to be hazardous and in the process of being redesigned.
The stability indices are as follows:
Note: Caution must be used when making use of Experimental
features,
particularly within modules that may be used as dependencies (or dependencies
of dependencies) within a Node.js application. End users may not be aware that
experimental features are being used, and therefore may experience unexpected
failures or behavior changes when API modifications occur. To help avoid such
surprises, Experimental
features may require a command-line flag to
explicitly enable them, or may cause a process warning to be emitted.
By default, such warnings are printed to stderr
and may be handled by
attaching a listener to the process.on('warning')
event.
JSON Output#
Every .html
document has a corresponding .json
document presenting
the same information in a structured manner. This feature is
experimental, and added for the benefit of IDEs and other utilities that
wish to do programmatic things with the documentation.
Syscalls and man pages#
System calls like open(2) and read(2) define the interface between user programs
and the underlying operating system. Node functions which simply wrap a syscall,
like fs.open()
, will document that. The docs link to the corresponding man
pages (short for manual pages) which describe how the syscalls work.
Some syscalls, like lchown(2), are BSD-specific. That means, for
example, that fs.lchown()
only works on macOS and other BSD-derived systems,
and is not available on Linux.
Most Unix syscalls have Windows equivalents, but behavior may differ on Windows relative to Linux and macOS. For an example of the subtle ways in which it's sometimes impossible to replace Unix syscall semantics on Windows, see Node issue 4760.
Usage#
node [options] [v8 options] [script.js | -e "script"] [arguments]
Please see the Command Line Options document for information about different options and ways to run scripts with Node.js.
Example#
An example of a web server written with Node.js which responds with
'Hello World'
:
const http = require('http');
const hostname = '127.0.0.1';
const port = 3000;
const server = http.createServer((req, res) => {
res.statusCode = 200;
res.setHeader('Content-Type', 'text/plain');
res.end('Hello World\n');
});
server.listen(port, hostname, () => {
console.log(`Server running at http://${hostname}:${port}/`);
});
To run the server, put the code into a file called example.js
and execute
it with Node.js:
$ node example.js
Server running at http://127.0.0.1:3000/
Many of the examples in the documentation can be run similarly.
C/C++ Addons#
Node.js Addons are dynamically-linked shared objects, written in C or C++, that
can be loaded into Node.js using the require()
function, and used
just as if they were an ordinary Node.js module. They are used primarily to
provide an interface between JavaScript running in Node.js and C/C++ libraries.
At the moment, the method for implementing Addons is rather complicated, involving knowledge of several components and APIs :
V8: the C++ library Node.js currently uses to provide the JavaScript implementation. V8 provides the mechanisms for creating objects, calling functions, etc. V8's API is documented mostly in the
v8.h
header file (deps/v8/include/v8.h
in the Node.js source tree), which is also available online.libuv: The C library that implements the Node.js event loop, its worker threads and all of the asynchronous behaviors of the platform. It also serves as a cross-platform abstraction library, giving easy, POSIX-like access across all major operating systems to many common system tasks, such as interacting with the filesystem, sockets, timers and system events. libuv also provides a pthreads-like threading abstraction that may be used to power more sophisticated asynchronous Addons that need to move beyond the standard event loop. Addon authors are encouraged to think about how to avoid blocking the event loop with I/O or other time-intensive tasks by off-loading work via libuv to non-blocking system operations, worker threads or a custom use of libuv's threads.
Internal Node.js libraries. Node.js itself exports a number of C/C++ APIs that Addons can use — the most important of which is the
node::ObjectWrap
class.Node.js includes a number of other statically linked libraries including OpenSSL. These other libraries are located in the
deps/
directory in the Node.js source tree. Only the V8 and OpenSSL symbols are purposefully re-exported by Node.js and may be used to various extents by Addons. See Linking to Node.js' own dependencies for additional information.
All of the following examples are available for download and may be used as a starting-point for your own Addon.
Hello world#
This "Hello world" example is a simple Addon, written in C++, that is the equivalent of the following JavaScript code:
module.exports.hello = () => 'world';
First, create the file hello.cc
:
// hello.cc
#include <node.h>
namespace demo {
using v8::FunctionCallbackInfo;
using v8::Isolate;
using v8::Local;
using v8::Object;
using v8::String;
using v8::Value;
void Method(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
args.GetReturnValue().Set(String::NewFromUtf8(isolate, "world"));
}
void init(Local<Object> exports) {
NODE_SET_METHOD(exports, "hello", Method);
}
NODE_MODULE(addon, init)
} // namespace demo
Note that all Node.js Addons must export an initialization function following the pattern:
void Initialize(Local<Object> exports);
NODE_MODULE(module_name, Initialize)
There is no semi-colon after NODE_MODULE
as it's not a function (see
node.h
).
The module_name
must match the filename of the final binary (excluding
the .node suffix).
In the hello.cc
example, then, the initialization function is init
and the
Addon module name is addon
.
Building#
Once the source code has been written, it must be compiled into the binary
addon.node
file. To do so, create a file called binding.gyp
in the
top-level of the project describing the build configuration of your module
using a JSON-like format. This file is used by node-gyp -- a tool written
specifically to compile Node.js Addons.
{
"targets": [
{
"target_name": "addon",
"sources": [ "hello.cc" ]
}
]
}
Note: A version of the node-gyp
utility is bundled and distributed with
Node.js as part of npm
. This version is not made directly available for
developers to use and is intended only to support the ability to use the
npm install
command to compile and install Addons. Developers who wish to
use node-gyp
directly can install it using the command
npm install -g node-gyp
. See the node-gyp
installation instructions for
more information, including platform-specific requirements.
Once the binding.gyp
file has been created, use node-gyp configure
to
generate the appropriate project build files for the current platform. This
will generate either a Makefile
(on Unix platforms) or a vcxproj
file
(on Windows) in the build/
directory.
Next, invoke the node-gyp build
command to generate the compiled addon.node
file. This will be put into the build/Release/
directory.
When using npm install
to install a Node.js Addon, npm uses its own bundled
version of node-gyp
to perform this same set of actions, generating a
compiled version of the Addon for the user's platform on demand.
Once built, the binary Addon can be used from within Node.js by pointing
require()
to the built addon.node
module:
// hello.js
const addon = require('./build/Release/addon');
console.log(addon.hello());
// Prints: 'world'
Please see the examples below for further information or https://github.com/arturadib/node-qt for an example in production.
Because the exact path to the compiled Addon binary can vary depending on how
it is compiled (i.e. sometimes it may be in ./build/Debug/
), Addons can use
the bindings package to load the compiled module.
Note that while the bindings
package implementation is more sophisticated
in how it locates Addon modules, it is essentially using a try-catch pattern
similar to:
try {
return require('./build/Release/addon.node');
} catch (err) {
return require('./build/Debug/addon.node');
}
Linking to Node.js' own dependencies#
Node.js uses a number of statically linked libraries such as V8, libuv and
OpenSSL. All Addons are required to link to V8 and may link to any of the
other dependencies as well. Typically, this is as simple as including
the appropriate #include <...>
statements (e.g. #include <v8.h>
) and
node-gyp
will locate the appropriate headers automatically. However, there
are a few caveats to be aware of:
When
node-gyp
runs, it will detect the specific release version of Node.js and download either the full source tarball or just the headers. If the full source is downloaded, Addons will have complete access to the full set of Node.js dependencies. However, if only the Node.js headers are downloaded, then only the symbols exported by Node.js will be available.node-gyp
can be run using the--nodedir
flag pointing at a local Node.js source image. Using this option, the Addon will have access to the full set of dependencies.
Loading Addons using require()#
The filename extension of the compiled Addon binary is .node
(as opposed
to .dll
or .so
). The require()
function is written to look for
files with the .node
file extension and initialize those as dynamically-linked
libraries.
When calling require()
, the .node
extension can usually be
omitted and Node.js will still find and initialize the Addon. One caveat,
however, is that Node.js will first attempt to locate and load modules or
JavaScript files that happen to share the same base name. For instance, if
there is a file addon.js
in the same directory as the binary addon.node
,
then require('addon')
will give precedence to the addon.js
file
and load it instead.
Native Abstractions for Node.js#
Each of the examples illustrated in this document make direct use of the Node.js and V8 APIs for implementing Addons. It is important to understand that the V8 API can, and has, changed dramatically from one V8 release to the next (and one major Node.js release to the next). With each change, Addons may need to be updated and recompiled in order to continue functioning. The Node.js release schedule is designed to minimize the frequency and impact of such changes but there is little that Node.js can do currently to ensure stability of the V8 APIs.
The Native Abstractions for Node.js (or nan
) provide a set of tools that
Addon developers are recommended to use to keep compatibility between past and
future releases of V8 and Node.js. See the nan
examples for an
illustration of how it can be used.
Addon examples#
Following are some example Addons intended to help developers get started. The examples make use of the V8 APIs. Refer to the online V8 reference for help with the various V8 calls, and V8's Embedder's Guide for an explanation of several concepts used such as handles, scopes, function templates, etc.
Each of these examples using the following binding.gyp
file:
{
"targets": [
{
"target_name": "addon",
"sources": [ "addon.cc" ]
}
]
}
In cases where there is more than one .cc
file, simply add the additional
filename to the sources
array. For example:
"sources": ["addon.cc", "myexample.cc"]
Once the binding.gyp
file is ready, the example Addons can be configured and
built using node-gyp
:
$ node-gyp configure build
Function arguments#
Addons will typically expose objects and functions that can be accessed from JavaScript running within Node.js. When functions are invoked from JavaScript, the input arguments and return value must be mapped to and from the C/C++ code.
The following example illustrates how to read function arguments passed from JavaScript and how to return a result:
// addon.cc
#include <node.h>
namespace demo {
using v8::Exception;
using v8::FunctionCallbackInfo;
using v8::Isolate;
using v8::Local;
using v8::Number;
using v8::Object;
using v8::String;
using v8::Value;
// This is the implementation of the "add" method
// Input arguments are passed using the
// const FunctionCallbackInfo<Value>& args struct
void Add(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
// Check the number of arguments passed.
if (args.Length() < 2) {
// Throw an Error that is passed back to JavaScript
isolate->ThrowException(Exception::TypeError(
String::NewFromUtf8(isolate, "Wrong number of arguments")));
return;
}
// Check the argument types
if (!args[0]->IsNumber() || !args[1]->IsNumber()) {
isolate->ThrowException(Exception::TypeError(
String::NewFromUtf8(isolate, "Wrong arguments")));
return;
}
// Perform the operation
double value = args[0]->NumberValue() + args[1]->NumberValue();
Local<Number> num = Number::New(isolate, value);
// Set the return value (using the passed in
// FunctionCallbackInfo<Value>&)
args.GetReturnValue().Set(num);
}
void Init(Local<Object> exports) {
NODE_SET_METHOD(exports, "add", Add);
}
NODE_MODULE(addon, Init)
} // namespace demo
Once compiled, the example Addon can be required and used from within Node.js:
// test.js
const addon = require('./build/Release/addon');
console.log('This should be eight:', addon.add(3, 5));
Callbacks#
It is common practice within Addons to pass JavaScript functions to a C++ function and execute them from there. The following example illustrates how to invoke such callbacks:
// addon.cc
#include <node.h>
namespace demo {
using v8::Function;
using v8::FunctionCallbackInfo;
using v8::Isolate;
using v8::Local;
using v8::Null;
using v8::Object;
using v8::String;
using v8::Value;
void RunCallback(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
Local<Function> cb = Local<Function>::Cast(args[0]);
const unsigned argc = 1;
Local<Value> argv[argc] = { String::NewFromUtf8(isolate, "hello world") };
cb->Call(Null(isolate), argc, argv);
}
void Init(Local<Object> exports, Local<Object> module) {
NODE_SET_METHOD(module, "exports", RunCallback);
}
NODE_MODULE(addon, Init)
} // namespace demo
Note that this example uses a two-argument form of Init()
that receives
the full module
object as the second argument. This allows the Addon
to completely overwrite exports
with a single function instead of
adding the function as a property of exports
.
To test it, run the following JavaScript:
// test.js
const addon = require('./build/Release/addon');
addon((msg) => {
console.log(msg);
// Prints: 'hello world'
});
Note that, in this example, the callback function is invoked synchronously.
Object factory#
Addons can create and return new objects from within a C++ function as
illustrated in the following example. An object is created and returned with a
property msg
that echoes the string passed to createObject()
:
// addon.cc
#include <node.h>
namespace demo {
using v8::FunctionCallbackInfo;
using v8::Isolate;
using v8::Local;
using v8::Object;
using v8::String;
using v8::Value;
void CreateObject(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
Local<Object> obj = Object::New(isolate);
obj->Set(String::NewFromUtf8(isolate, "msg"), args[0]->ToString());
args.GetReturnValue().Set(obj);
}
void Init(Local<Object> exports, Local<Object> module) {
NODE_SET_METHOD(module, "exports", CreateObject);
}
NODE_MODULE(addon, Init)
} // namespace demo
To test it in JavaScript:
// test.js
const addon = require('./build/Release/addon');
const obj1 = addon('hello');
const obj2 = addon('world');
console.log(obj1.msg, obj2.msg);
// Prints: 'hello world'
Function factory#
Another common scenario is creating JavaScript functions that wrap C++ functions and returning those back to JavaScript:
// addon.cc
#include <node.h>
namespace demo {
using v8::Function;
using v8::FunctionCallbackInfo;
using v8::FunctionTemplate;
using v8::Isolate;
using v8::Local;
using v8::Object;
using v8::String;
using v8::Value;
void MyFunction(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
args.GetReturnValue().Set(String::NewFromUtf8(isolate, "hello world"));
}
void CreateFunction(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
Local<FunctionTemplate> tpl = FunctionTemplate::New(isolate, MyFunction);
Local<Function> fn = tpl->GetFunction();
// omit this to make it anonymous
fn->SetName(String::NewFromUtf8(isolate, "theFunction"));
args.GetReturnValue().Set(fn);
}
void Init(Local<Object> exports, Local<Object> module) {
NODE_SET_METHOD(module, "exports", CreateFunction);
}
NODE_MODULE(addon, Init)
} // namespace demo
To test:
// test.js
const addon = require('./build/Release/addon');
const fn = addon();
console.log(fn());
// Prints: 'hello world'
Wrapping C++ objects#
It is also possible to wrap C++ objects/classes in a way that allows new
instances to be created using the JavaScript new
operator:
// addon.cc
#include <node.h>
#include "myobject.h"
namespace demo {
using v8::Local;
using v8::Object;
void InitAll(Local<Object> exports) {
MyObject::Init(exports);
}
NODE_MODULE(addon, InitAll)
} // namespace demo
Then, in myobject.h
, the wrapper class inherits from node::ObjectWrap
:
// myobject.h
#ifndef MYOBJECT_H
#define MYOBJECT_H
#include <node.h>
#include <node_object_wrap.h>
namespace demo {
class MyObject : public node::ObjectWrap {
public:
static void Init(v8::Local<v8::Object> exports);
private:
explicit MyObject(double value = 0);
~MyObject();
static void New(const v8::FunctionCallbackInfo<v8::Value>& args);
static void PlusOne(const v8::FunctionCallbackInfo<v8::Value>& args);
static v8::Persistent<v8::Function> constructor;
double value_;
};
} // namespace demo
#endif
In myobject.cc
, implement the various methods that are to be exposed.
Below, the method plusOne()
is exposed by adding it to the constructor's
prototype:
// myobject.cc
#include "myobject.h"
namespace demo {
using v8::Context;
using v8::Function;
using v8::FunctionCallbackInfo;
using v8::FunctionTemplate;
using v8::Isolate;
using v8::Local;
using v8::Number;
using v8::Object;
using v8::Persistent;
using v8::String;
using v8::Value;
Persistent<Function> MyObject::constructor;
MyObject::MyObject(double value) : value_(value) {
}
MyObject::~MyObject() {
}
void MyObject::Init(Local<Object> exports) {
Isolate* isolate = exports->GetIsolate();
// Prepare constructor template
Local<FunctionTemplate> tpl = FunctionTemplate::New(isolate, New);
tpl->SetClassName(String::NewFromUtf8(isolate, "MyObject"));
tpl->InstanceTemplate()->SetInternalFieldCount(1);
// Prototype
NODE_SET_PROTOTYPE_METHOD(tpl, "plusOne", PlusOne);
constructor.Reset(isolate, tpl->GetFunction());
exports->Set(String::NewFromUtf8(isolate, "MyObject"),
tpl->GetFunction());
}
void MyObject::New(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
if (args.IsConstructCall()) {
// Invoked as constructor: `new MyObject(...)`
double value = args[0]->IsUndefined() ? 0 : args[0]->NumberValue();
MyObject* obj = new MyObject(value);
obj->Wrap(args.This());
args.GetReturnValue().Set(args.This());
} else {
// Invoked as plain function `MyObject(...)`, turn into construct call.
const int argc = 1;
Local<Value> argv[argc] = { args[0] };
Local<Context> context = isolate->GetCurrentContext();
Local<Function> cons = Local<Function>::New(isolate, constructor);
Local<Object> result =
cons->NewInstance(context, argc, argv).ToLocalChecked();
args.GetReturnValue().Set(result);
}
}
void MyObject::PlusOne(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
MyObject* obj = ObjectWrap::Unwrap<MyObject>(args.Holder());
obj->value_ += 1;
args.GetReturnValue().Set(Number::New(isolate, obj->value_));
}
} // namespace demo
To build this example, the myobject.cc
file must be added to the
binding.gyp
:
{
"targets": [
{
"target_name": "addon",
"sources": [
"addon.cc",
"myobject.cc"
]
}
]
}
Test it with:
// test.js
const addon = require('./build/Release/addon');
const obj = new addon.MyObject(10);
console.log(obj.plusOne());
// Prints: 11
console.log(obj.plusOne());
// Prints: 12
console.log(obj.plusOne());
// Prints: 13
Factory of wrapped objects#
Alternatively, it is possible to use a factory pattern to avoid explicitly
creating object instances using the JavaScript new
operator:
const obj = addon.createObject();
// instead of:
// const obj = new addon.Object();
First, the createObject()
method is implemented in addon.cc
:
// addon.cc
#include <node.h>
#include "myobject.h"
namespace demo {
using v8::FunctionCallbackInfo;
using v8::Isolate;
using v8::Local;
using v8::Object;
using v8::String;
using v8::Value;
void CreateObject(const FunctionCallbackInfo<Value>& args) {
MyObject::NewInstance(args);
}
void InitAll(Local<Object> exports, Local<Object> module) {
MyObject::Init(exports->GetIsolate());
NODE_SET_METHOD(module, "exports", CreateObject);
}
NODE_MODULE(addon, InitAll)
} // namespace demo
In myobject.h
, the static method NewInstance()
is added to handle
instantiating the object. This method takes the place of using new
in
JavaScript:
// myobject.h
#ifndef MYOBJECT_H
#define MYOBJECT_H
#include <node.h>
#include <node_object_wrap.h>
namespace demo {
class MyObject : public node::ObjectWrap {
public:
static void Init(v8::Isolate* isolate);
static void NewInstance(const v8::FunctionCallbackInfo<v8::Value>& args);
private:
explicit MyObject(double value = 0);
~MyObject();
static void New(const v8::FunctionCallbackInfo<v8::Value>& args);
static void PlusOne(const v8::FunctionCallbackInfo<v8::Value>& args);
static v8::Persistent<v8::Function> constructor;
double value_;
};
} // namespace demo
#endif
The implementation in myobject.cc
is similar to the previous example:
// myobject.cc
#include <node.h>
#include "myobject.h"
namespace demo {
using v8::Context;
using v8::Function;
using v8::FunctionCallbackInfo;
using v8::FunctionTemplate;
using v8::Isolate;
using v8::Local;
using v8::Number;
using v8::Object;
using v8::Persistent;
using v8::String;
using v8::Value;
Persistent<Function> MyObject::constructor;
MyObject::MyObject(double value) : value_(value) {
}
MyObject::~MyObject() {
}
void MyObject::Init(Isolate* isolate) {
// Prepare constructor template
Local<FunctionTemplate> tpl = FunctionTemplate::New(isolate, New);
tpl->SetClassName(String::NewFromUtf8(isolate, "MyObject"));
tpl->InstanceTemplate()->SetInternalFieldCount(1);
// Prototype
NODE_SET_PROTOTYPE_METHOD(tpl, "plusOne", PlusOne);
constructor.Reset(isolate, tpl->GetFunction());
}
void MyObject::New(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
if (args.IsConstructCall()) {
// Invoked as constructor: `new MyObject(...)`
double value = args[0]->IsUndefined() ? 0 : args[0]->NumberValue();
MyObject* obj = new MyObject(value);
obj->Wrap(args.This());
args.GetReturnValue().Set(args.This());
} else {
// Invoked as plain function `MyObject(...)`, turn into construct call.
const int argc = 1;
Local<Value> argv[argc] = { args[0] };
Local<Function> cons = Local<Function>::New(isolate, constructor);
Local<Context> context = isolate->GetCurrentContext();
Local<Object> instance =
cons->NewInstance(context, argc, argv).ToLocalChecked();
args.GetReturnValue().Set(instance);
}
}
void MyObject::NewInstance(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
const unsigned argc = 1;
Local<Value> argv[argc] = { args[0] };
Local<Function> cons = Local<Function>::New(isolate, constructor);
Local<Context> context = isolate->GetCurrentContext();
Local<Object> instance =
cons->NewInstance(context, argc, argv).ToLocalChecked();
args.GetReturnValue().Set(instance);
}
void MyObject::PlusOne(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
MyObject* obj = ObjectWrap::Unwrap<MyObject>(args.Holder());
obj->value_ += 1;
args.GetReturnValue().Set(Number::New(isolate, obj->value_));
}
} // namespace demo
Once again, to build this example, the myobject.cc
file must be added to the
binding.gyp
:
{
"targets": [
{
"target_name": "addon",
"sources": [
"addon.cc",
"myobject.cc"
]
}
]
}
Test it with:
// test.js
const createObject = require('./build/Release/addon');
const obj = createObject(10);
console.log(obj.plusOne());
// Prints: 11
console.log(obj.plusOne());
// Prints: 12
console.log(obj.plusOne());
// Prints: 13
const obj2 = createObject(20);
console.log(obj2.plusOne());
// Prints: 21
console.log(obj2.plusOne());
// Prints: 22
console.log(obj2.plusOne());
// Prints: 23
Passing wrapped objects around#
In addition to wrapping and returning C++ objects, it is possible to pass
wrapped objects around by unwrapping them with the Node.js helper function
node::ObjectWrap::Unwrap
. The following examples shows a function add()
that can take two MyObject
objects as input arguments:
// addon.cc
#include <node.h>
#include <node_object_wrap.h>
#include "myobject.h"
namespace demo {
using v8::FunctionCallbackInfo;
using v8::Isolate;
using v8::Local;
using v8::Number;
using v8::Object;
using v8::String;
using v8::Value;
void CreateObject(const FunctionCallbackInfo<Value>& args) {
MyObject::NewInstance(args);
}
void Add(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
MyObject* obj1 = node::ObjectWrap::Unwrap<MyObject>(
args[0]->ToObject());
MyObject* obj2 = node::ObjectWrap::Unwrap<MyObject>(
args[1]->ToObject());
double sum = obj1->value() + obj2->value();
args.GetReturnValue().Set(Number::New(isolate, sum));
}
void InitAll(Local<Object> exports) {
MyObject::Init(exports->GetIsolate());
NODE_SET_METHOD(exports, "createObject", CreateObject);
NODE_SET_METHOD(exports, "add", Add);
}
NODE_MODULE(addon, InitAll)
} // namespace demo
In myobject.h
, a new public method is added to allow access to private values
after unwrapping the object.
// myobject.h
#ifndef MYOBJECT_H
#define MYOBJECT_H
#include <node.h>
#include <node_object_wrap.h>
namespace demo {
class MyObject : public node::ObjectWrap {
public:
static void Init(v8::Isolate* isolate);
static void NewInstance(const v8::FunctionCallbackInfo<v8::Value>& args);
inline double value() const { return value_; }
private:
explicit MyObject(double value = 0);
~MyObject();
static void New(const v8::FunctionCallbackInfo<v8::Value>& args);
static v8::Persistent<v8::Function> constructor;
double value_;
};
} // namespace demo
#endif
The implementation of myobject.cc
is similar to before:
// myobject.cc
#include <node.h>
#include "myobject.h"
namespace demo {
using v8::Context;
using v8::Function;
using v8::FunctionCallbackInfo;
using v8::FunctionTemplate;
using v8::Isolate;
using v8::Local;
using v8::Object;
using v8::Persistent;
using v8::String;
using v8::Value;
Persistent<Function> MyObject::constructor;
MyObject::MyObject(double value) : value_(value) {
}
MyObject::~MyObject() {
}
void MyObject::Init(Isolate* isolate) {
// Prepare constructor template
Local<FunctionTemplate> tpl = FunctionTemplate::New(isolate, New);
tpl->SetClassName(String::NewFromUtf8(isolate, "MyObject"));
tpl->InstanceTemplate()->SetInternalFieldCount(1);
constructor.Reset(isolate, tpl->GetFunction());
}
void MyObject::New(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
if (args.IsConstructCall()) {
// Invoked as constructor: `new MyObject(...)`
double value = args[0]->IsUndefined() ? 0 : args[0]->NumberValue();
MyObject* obj = new MyObject(value);
obj->Wrap(args.This());
args.GetReturnValue().Set(args.This());
} else {
// Invoked as plain function `MyObject(...)`, turn into construct call.
const int argc = 1;
Local<Value> argv[argc] = { args[0] };
Local<Context> context = isolate->GetCurrentContext();
Local<Function> cons = Local<Function>::New(isolate, constructor);
Local<Object> instance =
cons->NewInstance(context, argc, argv).ToLocalChecked();
args.GetReturnValue().Set(instance);
}
}
void MyObject::NewInstance(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
const unsigned argc = 1;
Local<Value> argv[argc] = { args[0] };
Local<Function> cons = Local<Function>::New(isolate, constructor);
Local<Context> context = isolate->GetCurrentContext();
Local<Object> instance =
cons->NewInstance(context, argc, argv).ToLocalChecked();
args.GetReturnValue().Set(instance);
}
} // namespace demo
Test it with:
// test.js
const addon = require('./build/Release/addon');
const obj1 = addon.createObject(10);
const obj2 = addon.createObject(20);
const result = addon.add(obj1, obj2);
console.log(result);
// Prints: 30
AtExit hooks#
An "AtExit" hook is a function that is invoked after the Node.js event loop
has ended but before the JavaScript VM is terminated and Node.js shuts down.
"AtExit" hooks are registered using the node::AtExit
API.
void AtExit(callback, args)#
callback
<void (*)(void*)> A pointer to the function to call at exit.args
<void*> A pointer to pass to the callback at exit.
Registers exit hooks that run after the event loop has ended but before the VM is killed.
AtExit takes two parameters: a pointer to a callback function to run at exit, and a pointer to untyped context data to be passed to that callback.
Callbacks are run in last-in first-out order.
The following addon.cc
implements AtExit:
// addon.cc
#include <assert.h>
#include <stdlib.h>
#include <node.h>
namespace demo {
using node::AtExit;
using v8::HandleScope;
using v8::Isolate;
using v8::Local;
using v8::Object;
static char cookie[] = "yum yum";
static int at_exit_cb1_called = 0;
static int at_exit_cb2_called = 0;
static void at_exit_cb1(void* arg) {
Isolate* isolate = static_cast<Isolate*>(arg);
HandleScope scope(isolate);
Local<Object> obj = Object::New(isolate);
assert(!obj.IsEmpty()); // assert VM is still alive
assert(obj->IsObject());
at_exit_cb1_called++;
}
static void at_exit_cb2(void* arg) {
assert(arg == static_cast<void*>(cookie));
at_exit_cb2_called++;
}
static void sanity_check(void*) {
assert(at_exit_cb1_called == 1);
assert(at_exit_cb2_called == 2);
}
void init(Local<Object> exports) {
AtExit(at_exit_cb2, cookie);
AtExit(at_exit_cb2, cookie);
AtExit(at_exit_cb1, exports->GetIsolate());
AtExit(sanity_check);
}
NODE_MODULE(addon, init)
} // namespace demo
Test in JavaScript by running:
// test.js
require('./build/Release/addon');
Assert#
The assert
module provides a simple set of assertion tests that can be used to
test invariants.
assert(value[, message])#
value
<any>message
<any>
An alias of assert.ok()
.
assert.deepEqual(actual, expected[, message])#
actual
<any>expected
<any>message
<any>
Tests for deep equality between the actual
and expected
parameters.
Primitive values are compared with the equal comparison operator ( ==
).
Only enumerable "own" properties are considered. The deepEqual()
implementation does not test object prototypes, attached symbols, or
non-enumerable properties. This can lead to some potentially surprising
results. For example, the following example does not throw an AssertionError
because the properties on the Error
object are non-enumerable:
// WARNING: This does not throw an AssertionError!
assert.deepEqual(Error('a'), Error('b'));
"Deep" equality means that the enumerable "own" properties of child objects are evaluated also:
const assert = require('assert');
const obj1 = {
a: {
b: 1
}
};
const obj2 = {
a: {
b: 2
}
};
const obj3 = {
a: {
b: 1
}
};
const obj4 = Object.create(obj1);
assert.deepEqual(obj1, obj1);
// OK, object is equal to itself
assert.deepEqual(obj1, obj2);
// AssertionError: { a: { b: 1 } } deepEqual { a: { b: 2 } }
// values of b are different
assert.deepEqual(obj1, obj3);
// OK, objects are equal
assert.deepEqual(obj1, obj4);
// AssertionError: { a: { b: 1 } } deepEqual {}
// Prototypes are ignored
If the values are not equal, an AssertionError
is thrown with a message
property set equal to the value of the message
parameter. If the message
parameter is undefined, a default error message is assigned.
assert.deepStrictEqual(actual, expected[, message])#
actual
<any>expected
<any>message
<any>
Generally identical to assert.deepEqual()
with two exceptions. First,
primitive values are compared using the strict equality operator ( ===
).
Second, object comparisons include a strict equality check of their prototypes.
const assert = require('assert');
assert.deepEqual({ a: 1 }, { a: '1' });
// OK, because 1 == '1'
assert.deepStrictEqual({ a: 1 }, { a: '1' });
// AssertionError: { a: 1 } deepStrictEqual { a: '1' }
// because 1 !== '1' using strict equality
If the values are not equal, an AssertionError
is thrown with a message
property set equal to the value of the message
parameter. If the message
parameter is undefined, a default error message is assigned.
assert.doesNotThrow(block[, error][, message])#
block
<Function>error
<RegExp> | <Function>message
<any>
Asserts that the function block
does not throw an error. See
assert.throws()
for more details.
When assert.doesNotThrow()
is called, it will immediately call the block
function.
If an error is thrown and it is the same type as that specified by the error
parameter, then an AssertionError
is thrown. If the error is of a different
type, or if the error
parameter is undefined, the error is propagated back
to the caller.
The following, for instance, will throw the TypeError
because there is no
matching error type in the assertion:
assert.doesNotThrow(
() => {
throw new TypeError('Wrong value');
},
SyntaxError
);
However, the following will result in an AssertionError
with the message
'Got unwanted exception (TypeError)..':
assert.doesNotThrow(
() => {
throw new TypeError('Wrong value');
},
TypeError
);
If an AssertionError
is thrown and a value is provided for the message
parameter, the value of message
will be appended to the AssertionError
message:
assert.doesNotThrow(
() => {
throw new TypeError('Wrong value');
},
TypeError,
'Whoops'
);
// Throws: AssertionError: Got unwanted exception (TypeError). Whoops
assert.equal(actual, expected[, message])#
actual
<any>expected
<any>message
<any>
Tests shallow, coercive equality between the actual
and expected
parameters
using the equal comparison operator ( ==
).
const assert = require('assert');
assert.equal(1, 1);
// OK, 1 == 1
assert.equal(1, '1');
// OK, 1 == '1'
assert.equal(1, 2);
// AssertionError: 1 == 2
assert.equal({a: {b: 1}}, {a: {b: 1}});
//AssertionError: { a: { b: 1 } } == { a: { b: 1 } }
If the values are not equal, an AssertionError
is thrown with a message
property set equal to the value of the message
parameter. If the message
parameter is undefined, a default error message is assigned.
assert.fail(message)#
assert.fail(actual, expected[, message[, operator[, stackStartFunction]]])#
actual
<any>expected
<any>message
<any>operator
<string> Default: '!='stackStartFunction
<function> Default:assert.fail
Throws an AssertionError
. If message
is falsy, the error message is set as
the values of actual
and expected
separated by the provided operator
.
Otherwise, the error message is the value of message
.
If stackStartFunction
is provided, all stack frames above that function will
be removed from stacktrace (see Error.captureStackTrace
).
const assert = require('assert');
assert.fail(1, 2, undefined, '>');
// AssertionError: 1 > 2
assert.fail(1, 2, 'fail');
// AssertionError: fail
assert.fail(1, 2, 'whoops', '>');
// AssertionError: whoops
assert.fail('boom');
// AssertionError: boom
assert.fail('a', 'b');
// AssertionError: 'a' != 'b'
Example use of stackStartFunction
for truncating the exception's stacktrace:
function suppressFrame() {
assert.fail('a', 'b', undefined, '!==', suppressFrame);
}
suppressFrame();
// AssertionError: 'a' !== 'b'
// at repl:1:1
// at ContextifyScript.Script.runInThisContext (vm.js:44:33)
// ...
assert.ifError(value)#
value
<any>
Throws value
if value
is truthy. This is useful when testing the error
argument in callbacks.
const assert = require('assert');
assert.ifError(null);
// OK
assert.ifError(0);
// OK
assert.ifError(1);
// Throws 1
assert.ifError('error');
// Throws 'error'
assert.ifError(new Error());
// Throws Error
assert.notDeepEqual(actual, expected[, message])#
actual
<any>expected
<any>message
<any>
Tests for any deep inequality. Opposite of assert.deepEqual()
.
const assert = require('assert');
const obj1 = {
a: {
b: 1
}
};
const obj2 = {
a: {
b: 2
}
};
const obj3 = {
a: {
b: 1
}
};
const obj4 = Object.create(obj1);
assert.notDeepEqual(obj1, obj1);
// AssertionError: { a: { b: 1 } } notDeepEqual { a: { b: 1 } }
assert.notDeepEqual(obj1, obj2);
// OK: obj1 and obj2 are not deeply equal
assert.notDeepEqual(obj1, obj3);
// AssertionError: { a: { b: 1 } } notDeepEqual { a: { b: 1 } }
assert.notDeepEqual(obj1, obj4);
// OK: obj1 and obj4 are not deeply equal
If the values are deeply equal, an AssertionError
is thrown with a message
property set equal to the value of the message
parameter. If the message
parameter is undefined, a default error message is assigned.
assert.notDeepStrictEqual(actual, expected[, message])#
actual
<any>expected
<any>message
<any>
Tests for deep strict inequality. Opposite of assert.deepStrictEqual()
.
const assert = require('assert');
assert.notDeepEqual({a: 1}, {a: '1'});
// AssertionError: { a: 1 } notDeepEqual { a: '1' }
assert.notDeepStrictEqual({a: 1}, {a: '1'});
// OK
If the values are deeply and strictly equal, an AssertionError
is thrown
with a message
property set equal to the value of the message
parameter. If
the message
parameter is undefined, a default error message is assigned.
assert.notEqual(actual, expected[, message])#
actual
<any>expected
<any>message
<any>
Tests shallow, coercive inequality with the not equal comparison operator
( !=
).
const assert = require('assert');
assert.notEqual(1, 2);
// OK
assert.notEqual(1, 1);
// AssertionError: 1 != 1
assert.notEqual(1, '1');
// AssertionError: 1 != '1'
If the values are equal, an AssertionError
is thrown with a message
property set equal to the value of the message
parameter. If the message
parameter is undefined, a default error message is assigned.
assert.notStrictEqual(actual, expected[, message])#
actual
<any>expected
<any>message
<any>
Tests strict inequality as determined by the strict not equal operator
( !==
).
const assert = require('assert');
assert.notStrictEqual(1, 2);
// OK
assert.notStrictEqual(1, 1);
// AssertionError: 1 !== 1
assert.notStrictEqual(1, '1');
// OK
If the values are strictly equal, an AssertionError
is thrown with a
message
property set equal to the value of the message
parameter. If the
message
parameter is undefined, a default error message is assigned.
assert.ok(value[, message])#
value
<any>message
<any>
Tests if value
is truthy. It is equivalent to
assert.equal(!!value, true, message)
.
If value
is not truthy, an AssertionError
is thrown with a message
property set equal to the value of the message
parameter. If the message
parameter is undefined
, a default error message is assigned.
const assert = require('assert');
assert.ok(true);
// OK
assert.ok(1);
// OK
assert.ok(false);
// throws "AssertionError: false == true"
assert.ok(0);
// throws "AssertionError: 0 == true"
assert.ok(false, 'it\'s false');
// throws "AssertionError: it's false"
assert.strictEqual(actual, expected[, message])#
actual
<any>expected
<any>message
<any>
Tests strict equality as determined by the strict equality operator ( ===
).
const assert = require('assert');
assert.strictEqual(1, 2);
// AssertionError: 1 === 2
assert.strictEqual(1, 1);
// OK
assert.strictEqual(1, '1');
// AssertionError: 1 === '1'
If the values are not strictly equal, an AssertionError
is thrown with a
message
property set equal to the value of the message
parameter. If the
message
parameter is undefined, a default error message is assigned.
assert.throws(block[, error][, message])#
block
<Function>error
<RegExp> | <Function>message
<any>
Expects the function block
to throw an error.
If specified, error
can be a constructor, RegExp
, or validation
function.
If specified, message
will be the message provided by the AssertionError
if
the block fails to throw.
Validate instanceof using constructor:
assert.throws(
() => {
throw new Error('Wrong value');
},
Error
);
Validate error message using RegExp
:
assert.throws(
() => {
throw new Error('Wrong value');
},
/value/
);
Custom error validation:
assert.throws(
() => {
throw new Error('Wrong value');
},
function(err) {
if ((err instanceof Error) && /value/.test(err)) {
return true;
}
},
'unexpected error'
);
Note that error
can not be a string. If a string is provided as the second
argument, then error
is assumed to be omitted and the string will be used for
message
instead. This can lead to easy-to-miss mistakes:
// THIS IS A MISTAKE! DO NOT DO THIS!
assert.throws(myFunction, 'missing foo', 'did not throw with expected message');
// Do this instead.
assert.throws(myFunction, /missing foo/, 'did not throw with expected message');
Buffer#
Prior to the introduction of TypedArray
in ECMAScript 2015
(ES6), the
JavaScript language had no mechanism for reading or manipulating streams
of binary data. The Buffer
class was introduced as part of the Node.js
API to make it possible to interact with octet streams in the context of things
like TCP streams and file system operations.
Now that TypedArray
has been added in ES6, the Buffer
class implements the
Uint8Array
API in a manner that is more optimized and suitable for Node.js'
use cases.
Instances of the Buffer
class are similar to arrays of integers but
correspond to fixed-sized, raw memory allocations outside the V8 heap.
The size of the Buffer
is established when it is created and cannot be
resized.
The Buffer
class is a global within Node.js, making it unlikely that one
would need to ever use require('buffer').Buffer
.
Examples:
// Creates a zero-filled Buffer of length 10.
const buf1 = Buffer.alloc(10);
// Creates a Buffer of length 10, filled with 0x1.
const buf2 = Buffer.alloc(10, 1);
// Creates an uninitialized buffer of length 10.
// This is faster than calling Buffer.alloc() but the returned
// Buffer instance might contain old data that needs to be
// overwritten using either fill() or write().
const buf3 = Buffer.allocUnsafe(10);
// Creates a Buffer containing [0x1, 0x2, 0x3].
const buf4 = Buffer.from([1, 2, 3]);
// Creates a Buffer containing UTF-8 bytes [0x74, 0xc3, 0xa9, 0x73, 0x74].
const buf5 = Buffer.from('tést');
// Creates a Buffer containing Latin-1 bytes [0x74, 0xe9, 0x73, 0x74].
const buf6 = Buffer.from('tést', 'latin1');
Buffer.from()
, Buffer.alloc()
, and Buffer.allocUnsafe()
#
In versions of Node.js prior to v6, Buffer
instances were created using the
Buffer
constructor function, which allocates the returned Buffer
differently based on what arguments are provided:
- Passing a number as the first argument to
Buffer()
(e.g.new Buffer(10)
), allocates a newBuffer
object of the specified size. The memory allocated for suchBuffer
instances is not initialized and can contain sensitive data. SuchBuffer
instances must be initialized manually by using eitherbuf.fill(0)
or by writing to theBuffer
completely. While this behavior is intentional to improve performance, development experience has demonstrated that a more explicit distinction is required between creating a fast-but-uninitializedBuffer
versus creating a slower-but-saferBuffer
. - Passing a string, array, or
Buffer
as the first argument copies the passed object's data into theBuffer
. - Passing an
ArrayBuffer
or aSharedArrayBuffer
returns aBuffer
that shares allocated memory with the given array buffer.
Because the behavior of new Buffer()
changes significantly based on the type
of value passed as the first argument, applications that do not properly
validate the input arguments passed to new Buffer()
, or that fail to
appropriately initialize newly allocated Buffer
content, can inadvertently
introduce security and reliability issues into their code.
To make the creation of Buffer
instances more reliable and less error prone,
the various forms of the new Buffer()
constructor have been deprecated
and replaced by separate Buffer.from()
, Buffer.alloc()
, and
Buffer.allocUnsafe()
methods.
Developers should migrate all existing uses of the new Buffer()
constructors
to one of these new APIs.
Buffer.from(array)
returns a newBuffer
containing a copy of the provided octets.Buffer.from(arrayBuffer[, byteOffset [, length]])
returns a newBuffer
that shares the same allocated memory as the givenArrayBuffer
.Buffer.from(buffer)
returns a newBuffer
containing a copy of the contents of the givenBuffer
.Buffer.from(string[, encoding])
returns a newBuffer
containing a copy of the provided string.Buffer.alloc(size[, fill[, encoding]])
returns a "filled"Buffer
instance of the specified size. This method can be significantly slower thanBuffer.allocUnsafe(size)
but ensures that newly createdBuffer
instances never contain old and potentially sensitive data.Buffer.allocUnsafe(size)
andBuffer.allocUnsafeSlow(size)
each return a newBuffer
of the specifiedsize
whose content must be initialized using eitherbuf.fill(0)
or written to completely.
Buffer
instances returned by Buffer.allocUnsafe()
may be allocated off
a shared internal memory pool if size
is less than or equal to half
Buffer.poolSize
. Instances returned by Buffer.allocUnsafeSlow()
never
use the shared internal memory pool.
The --zero-fill-buffers
command line option#
Node.js can be started using the --zero-fill-buffers
command line option to
force all newly allocated Buffer
instances created using either
new Buffer(size)
, Buffer.allocUnsafe()
, Buffer.allocUnsafeSlow()
or
new SlowBuffer(size)
to be automatically zero-filled upon creation. Use of
this flag changes the default behavior of these methods and can have a significant
impact on performance. Use of the --zero-fill-buffers
option is recommended
only when necessary to enforce that newly allocated Buffer
instances cannot
contain potentially sensitive data.
Example:
$ node --zero-fill-buffers
> Buffer.allocUnsafe(5);
<Buffer 00 00 00 00 00>
What makes Buffer.allocUnsafe()
and Buffer.allocUnsafeSlow()
"unsafe"?#
When calling Buffer.allocUnsafe()
and Buffer.allocUnsafeSlow()
, the
segment of allocated memory is uninitialized (it is not zeroed-out). While
this design makes the allocation of memory quite fast, the allocated segment of
memory might contain old data that is potentially sensitive. Using a Buffer
created by Buffer.allocUnsafe()
without completely overwriting the memory
can allow this old data to be leaked when the Buffer
memory is read.
While there are clear performance advantages to using Buffer.allocUnsafe()
,
extra care must be taken in order to avoid introducing security
vulnerabilities into an application.
Buffers and Character Encodings#
Buffer
instances are commonly used to represent sequences of encoded characters
such as UTF-8, UCS2, Base64 or even Hex-encoded data. It is possible to
convert back and forth between Buffer
instances and ordinary JavaScript strings
by using an explicit character encoding.
Example:
const buf = Buffer.from('hello world', 'ascii');
// Prints: 68656c6c6f20776f726c64
console.log(buf.toString('hex'));
// Prints: aGVsbG8gd29ybGQ=
console.log(buf.toString('base64'));
The character encodings currently supported by Node.js include:
'ascii'
- For 7-bit ASCII data only. This encoding is fast and will strip the high bit if set.'utf8'
- Multibyte encoded Unicode characters. Many web pages and other document formats use UTF-8.'utf16le'
- 2 or 4 bytes, little-endian encoded Unicode characters. Surrogate pairs (U+10000 to U+10FFFF) are supported.'ucs2'
- Alias of'utf16le'
.'base64'
- Base64 encoding. When creating aBuffer
from a string, this encoding will also correctly accept "URL and Filename Safe Alphabet" as specified in RFC4648, Section 5.'latin1'
- A way of encoding theBuffer
into a one-byte encoded string (as defined by the IANA in RFC1345, page 63, to be the Latin-1 supplement block and C0/C1 control codes).'binary'
- Alias for'latin1'
.'hex'
- Encode each byte as two hexadecimal characters.
Note: Today's browsers follow the WHATWG spec which aliases both 'latin1' and
ISO-8859-1 to win-1252. This means that while doing something like http.get()
,
if the returned charset is one of those listed in the WHATWG spec it's possible
that the server actually returned win-1252-encoded data, and using 'latin1'
encoding may incorrectly decode the characters.
Buffers and TypedArray#
Buffer
instances are also Uint8Array
instances. However, there are subtle
incompatibilities with the TypedArray specification in ECMAScript 2015
.
For example, while ArrayBuffer#slice()
creates a copy of the slice, the
implementation of Buffer#slice()
creates a view over the
existing Buffer
without copying, making Buffer#slice()
far
more efficient.
It is also possible to create new TypedArray
instances from a Buffer
with
the following caveats:
The
Buffer
object's memory is copied to theTypedArray
, not shared.The
Buffer
object's memory is interpreted as an array of distinct elements, and not as a byte array of the target type. That is,new Uint32Array(Buffer.from([1, 2, 3, 4]))
creates a 4-elementUint32Array
with elements[1, 2, 3, 4]
, not aUint32Array
with a single element[0x1020304]
or[0x4030201]
.
It is possible to create a new Buffer
that shares the same allocated memory as
a TypedArray
instance by using the TypeArray object's .buffer
property.
Example:
const arr = new Uint16Array(2);
arr[0] = 5000;
arr[1] = 4000;
// Copies the contents of `arr`
const buf1 = Buffer.from(arr);
// Shares memory with `arr`
const buf2 = Buffer.from(arr.buffer);
// Prints: <Buffer 88 a0>
console.log(buf1);
// Prints: <Buffer 88 13 a0 0f>
console.log(buf2);
arr[1] = 6000;
// Prints: <Buffer 88 a0>
console.log(buf1);
// Prints: <Buffer 88 13 70 17>
console.log(buf2);
Note that when creating a Buffer
using a TypedArray
's .buffer
, it is
possible to use only a portion of the underlying ArrayBuffer
by passing in
byteOffset
and length
parameters.
Example:
const arr = new Uint16Array(20);
const buf = Buffer.from(arr.buffer, 0, 16);
// Prints: 16
console.log(buf.length);
The Buffer.from()
and TypedArray.from()
have different signatures and
implementations. Specifically, the TypedArray
variants accept a second
argument that is a mapping function that is invoked on every element of the
typed array:
TypedArray.from(source[, mapFn[, thisArg]])
The Buffer.from()
method, however, does not support the use of a mapping
function:
Buffer.from(array)
Buffer.from(buffer)
Buffer.from(arrayBuffer[, byteOffset [, length]])
Buffer.from(string[, encoding])
Buffers and ES6 iteration#
Buffer
instances can be iterated over using the ECMAScript 2015
(ES6) for..of
syntax.
Example:
const buf = Buffer.from([1, 2, 3]);
// Prints:
// 1
// 2
// 3
for (const b of buf) {
console.log(b);
}
Additionally, the buf.values()
, buf.keys()
, and
buf.entries()
methods can be used to create iterators.
Class: Buffer#
The Buffer
class is a global type for dealing with binary data directly.
It can be constructed in a variety of ways.
new Buffer(array)#
Buffer.from(array)
instead.array
<integer[]> An array of bytes to copy from.
Allocates a new Buffer
using an array
of octets.
Example:
// Creates a new Buffer containing the UTF-8 bytes of the string 'buffer'
const buf = new Buffer([0x62, 0x75, 0x66, 0x66, 0x65, 0x72]);
new Buffer(buffer)#
Buffer.from(buffer)
instead.buffer
<Buffer> An existingBuffer
to copy data from.
Copies the passed buffer
data onto a new Buffer
instance.
Example:
const buf1 = new Buffer('buffer');
const buf2 = new Buffer(buf1);
buf1[0] = 0x61;
// Prints: auffer
console.log(buf1.toString());
// Prints: buffer
console.log(buf2.toString());
new Buffer(arrayBuffer[, byteOffset [, length]])#
Buffer.from(arrayBuffer[, byteOffset [, length]])
instead.arrayBuffer
<ArrayBuffer> | <SharedArrayBuffer> AnArrayBuffer
,SharedArrayBuffer
or the.buffer
property of aTypedArray
.byteOffset
<integer> Index of first byte to expose. Default:0
length
<integer> Number of bytes to expose. Default:arrayBuffer.length - byteOffset
This creates a view of the ArrayBuffer
or SharedArrayBuffer
without
copying the underlying memory. For example, when passed a reference to the
.buffer
property of a TypedArray
instance, the newly created Buffer
will
share the same allocated memory as the TypedArray
.
The optional byteOffset
and length
arguments specify a memory range within
the arrayBuffer
that will be shared by the Buffer
.
Example:
const arr = new Uint16Array(2);
arr[0] = 5000;
arr[1] = 4000;
// Shares memory with `arr`
const buf = new Buffer(arr.buffer);
// Prints: <Buffer 88 13 a0 0f>
console.log(buf);
// Changing the original Uint16Array changes the Buffer also
arr[1] = 6000;
// Prints: <Buffer 88 13 70 17>
console.log(buf);
new Buffer(size)#
size
<integer> The desired length of the newBuffer
.
Allocates a new Buffer
of size
bytes. The size
must be less than or equal
to the value of buffer.kMaxLength
. Otherwise, a RangeError
is thrown.
A zero-length Buffer
will be created if size <= 0
.
Unlike ArrayBuffers
, the underlying memory for Buffer
instances
created in this way is not initialized. The contents of a newly created Buffer
are unknown and could contain sensitive data. Use
Buffer.alloc(size)
instead to initialize a Buffer
to zeroes.
Example:
const buf = new Buffer(10);
// Prints: (contents may vary): <Buffer 48 21 4b 00 00 00 00 00 30 dd>
console.log(buf);
buf.fill(0);
// Prints: <Buffer 00 00 00 00 00 00 00 00 00 00>
console.log(buf);
new Buffer(string[, encoding])#
Buffer.from(string[, encoding])
instead.Creates a new Buffer
containing the given JavaScript string string
. If
provided, the encoding
parameter identifies the character encoding of string
.
Examples:
const buf1 = new Buffer('this is a tést');
// Prints: this is a tést
console.log(buf1.toString());
// Prints: this is a tC)st
console.log(buf1.toString('ascii'));
const buf2 = new Buffer('7468697320697320612074c3a97374', 'hex');
// Prints: this is a tést
console.log(buf2.toString());
Class Method: Buffer.alloc(size[, fill[, encoding]])#
size
<integer> The desired length of the newBuffer
.fill
<string> | <Buffer> | <integer> A value to pre-fill the newBuffer
with. Default:0
encoding
<string> Iffill
is a string, this is its encoding. Default:'utf8'
Allocates a new Buffer
of size
bytes. If fill
is undefined
, the
Buffer
will be zero-filled.
Example:
const buf = Buffer.alloc(5);
// Prints: <Buffer 00 00 00 00 00>
console.log(buf);
The size
must be less than or equal to the value of buffer.kMaxLength
.
Otherwise, a RangeError
is thrown. A zero-length Buffer
will be created if
size <= 0
.
If fill
is specified, the allocated Buffer
will be initialized by calling
buf.fill(fill)
.
Example:
const buf = Buffer.alloc(5, 'a');
// Prints: <Buffer 61 61 61 61 61>
console.log(buf);
If both fill
and encoding
are specified, the allocated Buffer
will be
initialized by calling buf.fill(fill, encoding)
.
Example:
const buf = Buffer.alloc(11, 'aGVsbG8gd29ybGQ=', 'base64');
// Prints: <Buffer 68 65 6c 6c 6f 20 77 6f 72 6c 64>
console.log(buf);
Calling Buffer.alloc()
can be significantly slower than the alternative
Buffer.allocUnsafe()
but ensures that the newly created Buffer
instance
contents will never contain sensitive data.
A TypeError
will be thrown if size
is not a number.
Class Method: Buffer.allocUnsafe(size)#
size
<integer> The desired length of the newBuffer
.
Allocates a new non-zero-filled Buffer
of size
bytes. The size
must
be less than or equal to the value of buffer.kMaxLength
. Otherwise, a
RangeError
is thrown. A zero-length Buffer
will be created if size <= 0
.
The underlying memory for Buffer
instances created in this way is not
initialized. The contents of the newly created Buffer
are unknown and
may contain sensitive data. Use Buffer.alloc()
instead to initialize
Buffer
instances to zeroes.
Example:
const buf = Buffer.allocUnsafe(10);
// Prints: (contents may vary): <Buffer a0 8b 28 3f 01 00 00 00 50 32>
console.log(buf);
buf.fill(0);
// Prints: <Buffer 00 00 00 00 00 00 00 00 00 00>
console.log(buf);
A TypeError
will be thrown if size
is not a number.
Note that the Buffer
module pre-allocates an internal Buffer
instance of
size Buffer.poolSize
that is used as a pool for the fast allocation of new
Buffer
instances created using Buffer.allocUnsafe()
and the deprecated
new Buffer(size)
constructor only when size
is less than or equal to
Buffer.poolSize >> 1
(floor of Buffer.poolSize
divided by two).
Use of this pre-allocated internal memory pool is a key difference between
calling Buffer.alloc(size, fill)
vs. Buffer.allocUnsafe(size).fill(fill)
.
Specifically, Buffer.alloc(size, fill)
will never use the internal Buffer
pool, while Buffer.allocUnsafe(size).fill(fill)
will use the internal
Buffer
pool if size
is less than or equal to half Buffer.poolSize
. The
difference is subtle but can be important when an application requires the
additional performance that Buffer.allocUnsafe()
provides.
Class Method: Buffer.allocUnsafeSlow(size)#
size
<integer> The desired length of the newBuffer
.
Allocates a new non-zero-filled and non-pooled Buffer
of size
bytes. The
size
must be less than or equal to the value of buffer.kMaxLength
.
Otherwise, a RangeError
is thrown. A zero-length Buffer
will be created if
size <= 0
.
The underlying memory for Buffer
instances created in this way is not
initialized. The contents of the newly created Buffer
are unknown and
may contain sensitive data. Use buf.fill(0)
to initialize such
Buffer
instances to zeroes.
When using Buffer.allocUnsafe()
to allocate new Buffer
instances,
allocations under 4KB are, by default, sliced from a single pre-allocated
Buffer
. This allows applications to avoid the garbage collection overhead of
creating many individually allocated Buffer
instances. This approach improves
both performance and memory usage by eliminating the need to track and cleanup as
many Persistent
objects.
However, in the case where a developer may need to retain a small chunk of
memory from a pool for an indeterminate amount of time, it may be appropriate
to create an un-pooled Buffer
instance using Buffer.allocUnsafeSlow()
then
copy out the relevant bits.
Example:
// Need to keep around a few small chunks of memory
const store = [];
socket.on('readable', () => {
const data = socket.read();
// Allocate for retained data
const sb = Buffer.allocUnsafeSlow(10);
// Copy the data into the new allocation
data.copy(sb, 0, 0, 10);
store.push(sb);
});
Use of Buffer.allocUnsafeSlow()
should be used only as a last resort after
a developer has observed undue memory retention in their applications.
A TypeError
will be thrown if size
is not a number.
Class Method: Buffer.byteLength(string[, encoding])#
string
<string> | <Buffer> | <TypedArray> | <DataView> | <ArrayBuffer> | <SharedArrayBuffer> A value to calculate the length of.encoding
<string> Ifstring
is a string, this is its encoding. Default:'utf8'
- Returns: <integer> The number of bytes contained within
string
.
Returns the actual byte length of a string. This is not the same as
String.prototype.length
since that returns the number of characters in
a string.
Note that for 'base64'
and 'hex'
, this function assumes valid input. For
strings that contain non-Base64/Hex-encoded data (e.g. whitespace), the return
value might be greater than the length of a Buffer
created from the string.
Example:
const str = '\u00bd + \u00bc = \u00be';
// Prints: ½ + ¼ = ¾: 9 characters, 12 bytes
console.log(`${str}: ${str.length} characters, ` +
`${Buffer.byteLength(str, 'utf8')} bytes`);
When string
is a Buffer
/DataView
/TypedArray
/ArrayBuffer
/
SharedArrayBuffer
, the actual byte length is returned.
Otherwise, converts to String
and returns the byte length of string.
Class Method: Buffer.compare(buf1, buf2)#
Compares buf1
to buf2
typically for the purpose of sorting arrays of
Buffer
instances. This is equivalent to calling
buf1.compare(buf2)
.
Example:
const buf1 = Buffer.from('1234');
const buf2 = Buffer.from('0123');
const arr = [buf1, buf2];
// Prints: [ <Buffer 30 31 32 33>, <Buffer 31 32 33 34> ]
// (This result is equal to: [buf2, buf1])
console.log(arr.sort(Buffer.compare));
Class Method: Buffer.concat(list[, totalLength])#
list
<Array> List ofBuffer
instances to concat.totalLength
<integer> Total length of theBuffer
instances inlist
when concatenated.- Returns: <Buffer>
Returns a new Buffer
which is the result of concatenating all the Buffer
instances in the list
together.
If the list has no items, or if the totalLength
is 0, then a new zero-length
Buffer
is returned.
If totalLength
is not provided, it is calculated from the Buffer
instances
in list
. This however causes an additional loop to be executed in order to
calculate the totalLength
, so it is faster to provide the length explicitly if
it is already known.
If totalLength
is provided, it is coerced to an unsigned integer. If the
combined length of the Buffer
s in list
exceeds totalLength
, the result is
truncated to totalLength
.
Example: Create a single Buffer
from a list of three Buffer
instances
const buf1 = Buffer.alloc(10);
const buf2 = Buffer.alloc(14);
const buf3 = Buffer.alloc(18);
const totalLength = buf1.length + buf2.length + buf3.length;
// Prints: 42
console.log(totalLength);
const bufA = Buffer.concat([buf1, buf2, buf3], totalLength);
// Prints: <Buffer 00 00 00 00 ...>
console.log(bufA);
// Prints: 42
console.log(bufA.length);
Class Method: Buffer.from(array)#
array
<Array>
Allocates a new Buffer
using an array
of octets.
Example:
// Creates a new Buffer containing UTF-8 bytes of the string 'buffer'
const buf = Buffer.from([0x62, 0x75, 0x66, 0x66, 0x65, 0x72]);
A TypeError
will be thrown if array
is not an Array
.
Class Method: Buffer.from(arrayBuffer[, byteOffset[, length]])#
arrayBuffer
<ArrayBuffer> | <SharedArrayBuffer> AnArrayBuffer
,SharedArrayBuffer
, or the.buffer
property of aTypedArray
.byteOffset
<integer> Index of first byte to expose. Default:0
length
<integer> Number of bytes to expose. Default:arrayBuffer.length - byteOffset
This creates a view of the ArrayBuffer
without copying the underlying
memory. For example, when passed a reference to the .buffer
property of a
TypedArray
instance, the newly created Buffer
will share the same
allocated memory as the TypedArray
.
Example:
const arr = new Uint16Array(2);
arr[0] = 5000;
arr[1] = 4000;
// Shares memory with `arr`
const buf = Buffer.from(arr.buffer);
// Prints: <Buffer 88 13 a0 0f>
console.log(buf);
// Changing the original Uint16Array changes the Buffer also
arr[1] = 6000;
// Prints: <Buffer 88 13 70 17>
console.log(buf);
The optional byteOffset
and length
arguments specify a memory range within
the arrayBuffer
that will be shared by the Buffer
.
Example:
const ab = new ArrayBuffer(10);
const buf = Buffer.from(ab, 0, 2);
// Prints: 2
console.log(buf.length);
A TypeError
will be thrown if arrayBuffer
is not an ArrayBuffer
or a
SharedArrayBuffer
.
Class Method: Buffer.from(buffer)#
buffer
<Buffer> An existingBuffer
to copy data from.
Copies the passed buffer
data onto a new Buffer
instance.
Example:
const buf1 = Buffer.from('buffer');
const buf2 = Buffer.from(buf1);
buf1[0] = 0x61;
// Prints: auffer
console.log(buf1.toString());
// Prints: buffer
console.log(buf2.toString());
A TypeError
will be thrown if buffer
is not a Buffer
.
Class Method: Buffer.from(string[, encoding])#
Creates a new Buffer
containing the given JavaScript string string
. If
provided, the encoding
parameter identifies the character encoding of string
.
Examples:
const buf1 = Buffer.from('this is a tést');
// Prints: this is a tést
console.log(buf1.toString());
// Prints: this is a tC)st
console.log(buf1.toString('ascii'));
const buf2 = Buffer.from('7468697320697320612074c3a97374', 'hex');
// Prints: this is a tést
console.log(buf2.toString());
A TypeError
will be thrown if string
is not a string.
Class Method: Buffer.isBuffer(obj)#
Returns true
if obj
is a Buffer
, false
otherwise.
Class Method: Buffer.isEncoding(encoding)#
Returns true
if encoding
contains a supported character encoding, or false
otherwise.
Class Property: Buffer.poolSize#
- <integer> Default:
8192
This is the number of bytes used to determine the size of pre-allocated, internal
Buffer
instances used for pooling. This value may be modified.
buf[index]#
The index operator [index]
can be used to get and set the octet at position
index
in buf
. The values refer to individual bytes, so the legal value
range is between 0x00
and 0xFF
(hex) or 0
and 255
(decimal).
This operator is inherited from Uint8Array
, so its behavior on out-of-bounds
access is the same as UInt8Array
- that is, getting returns undefined
and
setting does nothing.
Example: Copy an ASCII string into a Buffer
, one byte at a time
const str = 'Node.js';
const buf = Buffer.allocUnsafe(str.length);
for (let i = 0; i < str.length; i++) {
buf[i] = str.charCodeAt(i);
}
// Prints: Node.js
console.log(buf.toString('ascii'));
buf.compare(target[, targetStart[, targetEnd[, sourceStart[, sourceEnd]]]])#
target
<Buffer> ABuffer
to compare to.targetStart
<integer> The offset withintarget
at which to begin comparison. Default:0
targetEnd
<integer> The offset withtarget
at which to end comparison (not inclusive). Default:target.length
sourceStart
<integer> The offset withinbuf
at which to begin comparison. Default:0
sourceEnd
<integer> The offset withinbuf
at which to end comparison (not inclusive). Default:buf.length
- Returns: <integer>
Compares buf
with target
and returns a number indicating whether buf
comes before, after, or is the same as target
in sort order.
Comparison is based on the actual sequence of bytes in each Buffer
.
0
is returned iftarget
is the same asbuf
1
is returned iftarget
should come beforebuf
when sorted.-1
is returned iftarget
should come afterbuf
when sorted.
Examples:
const buf1 = Buffer.from('ABC');
const buf2 = Buffer.from('BCD');
const buf3 = Buffer.from('ABCD');
// Prints: 0
console.log(buf1.compare(buf1));
// Prints: -1
console.log(buf1.compare(buf2));
// Prints: -1
console.log(buf1.compare(buf3));
// Prints: 1
console.log(buf2.compare(buf1));
// Prints: 1
console.log(buf2.compare(buf3));
// Prints: [ <Buffer 41 42 43>, <Buffer 41 42 43 44>, <Buffer 42 43 44> ]
// (This result is equal to: [buf1, buf3, buf2])
console.log([buf1, buf2, buf3].sort(Buffer.compare));
The optional targetStart
, targetEnd
, sourceStart
, and sourceEnd
arguments can be used to limit the comparison to specific ranges within target
and buf
respectively.
Examples:
const buf1 = Buffer.from([1, 2, 3, 4, 5, 6, 7, 8, 9]);
const buf2 = Buffer.from([5, 6, 7, 8, 9, 1, 2, 3, 4]);
// Prints: 0
console.log(buf1.compare(buf2, 5, 9, 0, 4));
// Prints: -1
console.log(buf1.compare(buf2, 0, 6, 4));
// Prints: 1
console.log(buf1.compare(buf2, 5, 6, 5));
A RangeError
will be thrown if: targetStart < 0
, sourceStart < 0
,
targetEnd > target.byteLength
or sourceEnd > source.byteLength
.
buf.copy(target[, targetStart[, sourceStart[, sourceEnd]]])#
target
<Buffer> | <Uint8Array> ABuffer
orUint8Array
to copy into.targetStart
<integer> The offset withintarget
at which to begin copying to. Default:0
sourceStart
<integer> The offset withinbuf
at which to begin copying from. Default:0
sourceEnd
<integer> The offset withinbuf
at which to stop copying (not inclusive). Default:buf.length
- Returns: <integer> The number of bytes copied.
Copies data from a region of buf
to a region in target
even if the target
memory region overlaps with buf
.
Example: Create two Buffer
instances, buf1
and buf2
, and copy buf1
from
byte 16 through byte 19 into buf2
, starting at the 8th byte in buf2
const buf1 = Buffer.allocUnsafe(26);
const buf2 = Buffer.allocUnsafe(26).fill('!');
for (let i = 0; i < 26; i++) {
// 97 is the decimal ASCII value for 'a'
buf1[i] = i + 97;
}
buf1.copy(buf2, 8, 16, 20);
// Prints: !!!!!!!!qrst!!!!!!!!!!!!!
console.log(buf2.toString('ascii', 0, 25));
Example: Create a single Buffer
and copy data from one region to an
overlapping region within the same Buffer
const buf = Buffer.allocUnsafe(26);
for (let i = 0; i < 26; i++) {
// 97 is the decimal ASCII value for 'a'
buf[i] = i + 97;
}
buf.copy(buf, 0, 4, 10);
// Prints: efghijghijklmnopqrstuvwxyz
console.log(buf.toString());
buf.entries()#
- Returns: <Iterator>
Creates and returns an iterator of [index, byte]
pairs from the contents of
buf
.
Example: Log the entire contents of a Buffer
const buf = Buffer.from('buffer');
// Prints:
// [0, 98]
// [1, 117]
// [2, 102]
// [3, 102]
// [4, 101]
// [5, 114]
for (const pair of buf.entries()) {
console.log(pair);
}
buf.equals(otherBuffer)#
Returns true
if both buf
and otherBuffer
have exactly the same bytes,
false
otherwise.
Examples:
const buf1 = Buffer.from('ABC');
const buf2 = Buffer.from('414243', 'hex');
const buf3 = Buffer.from('ABCD');
// Prints: true
console.log(buf1.equals(buf2));
// Prints: false
console.log(buf1.equals(buf3));
buf.fill(value[, offset[, end]][, encoding])#
value
<string> | <Buffer> | <integer> The value to fillbuf
with.offset
<integer> Number of bytes to skip before starting to fillbuf
. Default:0
end
<integer> Where to stop fillingbuf
(not inclusive). Default:buf.length
encoding
<string> Ifvalue
is a string, this is its encoding. Default:'utf8'
- Returns: <Buffer> A reference to
buf
.
Fills buf
with the specified value
. If the offset
and end
are not given,
the entire buf
will be filled. This is meant to be a small simplification to
allow the creation and filling of a Buffer
to be done on a single line.
Example: Fill a Buffer
with the ASCII character 'h'
const b = Buffer.allocUnsafe(50).fill('h');
// Prints: hhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh
console.log(b.toString());
value
is coerced to a uint32
value if it is not a String or Integer.
If the final write of a fill()
operation falls on a multi-byte character,
then only the first bytes of that character that fit into buf
are written.
Example: Fill a Buffer
with a two-byte character
// Prints: <Buffer c8 a2 c8>
console.log(Buffer.allocUnsafe(3).fill('\u0222'));
buf.includes(value[, byteOffset][, encoding])#
value
<string> | <Buffer> | <integer> What to search for.byteOffset
<integer> Where to begin searching inbuf
. Default:0
encoding
<string> Ifvalue
is a string, this is its encoding. Default:'utf8'
- Returns: <boolean>
true
ifvalue
was found inbuf
,false
otherwise.
Equivalent to buf.indexOf() !== -1
.
Examples:
const buf = Buffer.from('this is a buffer');
// Prints: true
console.log(buf.includes('this'));
// Prints: true
console.log(buf.includes('is'));
// Prints: true
console.log(buf.includes(Buffer.from('a buffer')));
// Prints: true
// (97 is the decimal ASCII value for 'a')
console.log(buf.includes(97));
// Prints: false
console.log(buf.includes(Buffer.from('a buffer example')));
// Prints: true
console.log(buf.includes(Buffer.from('a buffer example').slice(0, 8)));
// Prints: false
console.log(buf.includes('this', 4));
buf.indexOf(value[, byteOffset][, encoding])#
value
<string> | <Buffer> | <integer> What to search for.byteOffset
<integer> Where to begin searching inbuf
. Default:0
encoding
<string> Ifvalue
is a string, this is its encoding. Default:'utf8'
- Returns: <integer> The index of the first occurrence of
value
inbuf
or-1
ifbuf
does not containvalue
.
If value
is:
- a string,
value
is interpreted according to the character encoding inencoding
. - a
Buffer
,value
will be used in its entirety. To compare a partialBuffer
usebuf.slice()
. - a number,
value
will be interpreted as an unsigned 8-bit integer value between0
and255
.
Examples:
const buf = Buffer.from('this is a buffer');
// Prints: 0
console.log(buf.indexOf('this'));
// Prints: 2
console.log(buf.indexOf('is'));
// Prints: 8
console.log(buf.indexOf(Buffer.from('a buffer')));
// Prints: 8
// (97 is the decimal ASCII value for 'a')
console.log(buf.indexOf(97));
// Prints: -1
console.log(buf.indexOf(Buffer.from('a buffer example')));
// Prints: 8
console.log(buf.indexOf(Buffer.from('a buffer example').slice(0, 8)));
const utf16Buffer = Buffer.from('\u039a\u0391\u03a3\u03a3\u0395', 'ucs2');
// Prints: 4
console.log(utf16Buffer.indexOf('\u03a3', 0, 'ucs2'));
// Prints: 6
console.log(utf16Buffer.indexOf('\u03a3', -4, 'ucs2'));
If value
is not a string, number, or Buffer
, this method will throw a
TypeError
. If value
is a number, it will be coerced to a valid byte value,
an integer between 0 and 255.
If byteOffset
is not a number, it will be coerced to a number. Any arguments
that coerce to NaN
or 0, like {}
, []
, null
or undefined
, will search
the whole buffer. This behavior matches String#indexOf()
.
const b = Buffer.from('abcdef');
// Passing a value that's a number, but not a valid byte
// Prints: 2, equivalent to searching for 99 or 'c'
console.log(b.indexOf(99.9));
console.log(b.indexOf(256 + 99));
// Passing a byteOffset that coerces to NaN or 0
// Prints: 1, searching the whole buffer
console.log(b.indexOf('b', undefined));
console.log(b.indexOf('b', {}));
console.log(b.indexOf('b', null));
console.log(b.indexOf('b', []));
buf.includes(value[, byteOffset][, encoding])#
value
<String> | <Buffer> | <Integer> What to search for.byteOffset
<Integer> Where to begin searching inbuf
. Default:0
encoding
<String> Ifvalue
is a string, this is its encoding. Default:'utf8'
- Returns: <Boolean>
true
ifvalue
was found inbuf
,false
otherwise
Equivalent to buf.indexOf() !== -1
.
Examples:
const buf = Buffer.from('this is a buffer');
// Prints: true
console.log(buf.includes('this'));
// Prints: true
console.log(buf.includes('is'));
// Prints: true
console.log(buf.includes(Buffer.from('a buffer')));
// Prints: true
// (97 is the decimal ASCII value for 'a')
console.log(buf.includes(97));
// Prints: false
console.log(buf.includes(Buffer.from('a buffer example')));
// Prints: true
console.log(buf.includes(Buffer.from('a buffer example').slice(0, 8)));
// Prints: false
console.log(buf.includes('this', 4));
buf.keys()#
- Returns: <Iterator>
Creates and returns an iterator of buf
keys (indices).
Example:
const buf = Buffer.from('buffer');
// Prints:
// 0
// 1
// 2
// 3
// 4
// 5
for (const key of buf.keys()) {
console.log(key);
}
buf.lastIndexOf(value[, byteOffset][, encoding])#
value
<string> | <Buffer> | <integer> What to search for.byteOffset
<integer> Where to begin searching inbuf
. Default:buf.length
- 1
encoding
<string> Ifvalue
is a string, this is its encoding. Default:'utf8'
- Returns: <integer> The index of the last occurrence of
value
inbuf
or-1
ifbuf
does not containvalue
.
Identical to buf.indexOf()
, except buf
is searched from back to front
instead of front to back.
Examples:
const buf = Buffer.from('this buffer is a buffer');
// Prints: 0
console.log(buf.lastIndexOf('this'));
// Prints: 17
console.log(buf.lastIndexOf('buffer'));
// Prints: 17
console.log(buf.lastIndexOf(Buffer.from('buffer')));
// Prints: 15
// (97 is the decimal ASCII value for 'a')
console.log(buf.lastIndexOf(97));
// Prints: -1
console.log(buf.lastIndexOf(Buffer.from('yolo')));
// Prints: 5
console.log(buf.lastIndexOf('buffer', 5));
// Prints: -1
console.log(buf.lastIndexOf('buffer', 4));
const utf16Buffer = Buffer.from('\u039a\u0391\u03a3\u03a3\u0395', 'ucs2');
// Prints: 6
console.log(utf16Buffer.lastIndexOf('\u03a3', undefined, 'ucs2'));
// Prints: 4
console.log(utf16Buffer.lastIndexOf('\u03a3', -5, 'ucs2'));
If value
is not a string, number, or Buffer
, this method will throw a
TypeError
. If value
is a number, it will be coerced to a valid byte value,
an integer between 0 and 255.
If byteOffset
is not a number, it will be coerced to a number. Any arguments
that coerce to NaN
, like {}
or undefined
, will search the whole buffer.
This behavior matches String#lastIndexOf()
.
const b = Buffer.from('abcdef');
// Passing a value that's a number, but not a valid byte
// Prints: 2, equivalent to searching for 99 or 'c'
console.log(b.lastIndexOf(99.9));
console.log(b.lastIndexOf(256 + 99));
// Passing a byteOffset that coerces to NaN
// Prints: 1, searching the whole buffer
console.log(b.lastIndexOf('b', undefined));
console.log(b.lastIndexOf('b', {}));
// Passing a byteOffset that coerces to 0
// Prints: -1, equivalent to passing 0
console.log(b.lastIndexOf('b', null));
console.log(b.lastIndexOf('b', []));
buf.length#
Returns the amount of memory allocated for buf
in bytes. Note that this
does not necessarily reflect the amount of "usable" data within buf
.
Example: Create a Buffer
and write a shorter ASCII string to it
const buf = Buffer.alloc(1234);
// Prints: 1234
console.log(buf.length);
buf.write('some string', 0, 'ascii');
// Prints: 1234
console.log(buf.length);
While the length
property is not immutable, changing the value of length
can result in undefined and inconsistent behavior. Applications that wish to
modify the length of a Buffer
should therefore treat length
as read-only and
use buf.slice()
to create a new Buffer
.
Examples:
let buf = Buffer.allocUnsafe(10);
buf.write('abcdefghj', 0, 'ascii');
// Prints: 10
console.log(buf.length);
buf = buf.slice(0, 5);
// Prints: 5
console.log(buf.length);
buf.readDoubleBE(offset[, noAssert])#
buf.readDoubleLE(offset[, noAssert])#
offset
<integer> Number of bytes to skip before starting to read. Must satisfy:0 <= offset <= buf.length - 8
.noAssert
<boolean> Skipoffset
validation? Default:false
- Returns: <number>
Reads a 64-bit double from buf
at the specified offset
with specified
endian format (readDoubleBE()
returns big endian, readDoubleLE()
returns
little endian).
Setting noAssert
to true
allows offset
to be beyond the end of buf
, but
the resulting behavior is undefined.
Examples:
const buf = Buffer.from([1, 2, 3, 4, 5, 6, 7, 8]);
// Prints: 8.20788039913184e-304
console.log(buf.readDoubleBE());
// Prints: 5.447603722011605e-270
console.log(buf.readDoubleLE());
// Throws an exception: RangeError: Index out of range
console.log(buf.readDoubleLE(1));
// Warning: reads passed end of buffer!
// This will result in a segmentation fault! Don't do this!
console.log(buf.readDoubleLE(1, true));
buf.readFloatBE(offset[, noAssert])#
buf.readFloatLE(offset[, noAssert])#
offset
<integer> Number of bytes to skip before starting to read. Must satisfy:0 <= offset <= buf.length - 4
.noAssert
<boolean> Skipoffset
validation? Default:false
- Returns: <number>
Reads a 32-bit float from buf
at the specified offset
with specified
endian format (readFloatBE()
returns big endian, readFloatLE()
returns
little endian).
Setting noAssert
to true
allows offset
to be beyond the end of buf
, but
the resulting behavior is undefined.
Examples:
const buf = Buffer.from([1, 2, 3, 4]);
// Prints: 2.387939260590663e-38
console.log(buf.readFloatBE());
// Prints: 1.539989614439558e-36
console.log(buf.readFloatLE());
// Throws an exception: RangeError: Index out of range
console.log(buf.readFloatLE(1));
// Warning: reads passed end of buffer!
// This will result in a segmentation fault! Don't do this!
console.log(buf.readFloatLE(1, true));
buf.readInt8(offset[, noAssert])#
offset
<integer> Number of bytes to skip before starting to read. Must satisfy:0 <= offset <= buf.length - 1
.noAssert
<boolean> Skipoffset
validation? Default:false
- Returns: <integer>
Reads a signed 8-bit integer from buf
at the specified offset
.
Setting noAssert
to true
allows offset
to be beyond the end of buf
, but
the resulting behavior is undefined.
Integers read from a Buffer
are interpreted as two's complement signed values.
Examples:
const buf = Buffer.from([-1, 5]);
// Prints: -1
console.log(buf.readInt8(0));
// Prints: 5
console.log(buf.readInt8(1));
// Throws an exception: RangeError: Index out of range
console.log(buf.readInt8(2));
buf.readInt16BE(offset[, noAssert])#
buf.readInt16LE(offset[, noAssert])#
offset
<integer> Number of bytes to skip before starting to read. Must satisfy:0 <= offset <= buf.length - 2
.noAssert
<boolean> Skipoffset
validation? Default:false
- Returns: <integer>
Reads a signed 16-bit integer from buf
at the specified offset
with
the specified endian format (readInt16BE()
returns big endian,
readInt16LE()
returns little endian).
Setting noAssert
to true
allows offset
to be beyond the end of buf
, but
the resulting behavior is undefined.
Integers read from a Buffer
are interpreted as two's complement signed values.
Examples:
const buf = Buffer.from([0, 5]);
// Prints: 5
console.log(buf.readInt16BE());
// Prints: 1280
console.log(buf.readInt16LE());
// Throws an exception: RangeError: Index out of range
console.log(buf.readInt16LE(1));
buf.readInt32BE(offset[, noAssert])#
buf.readInt32LE(offset[, noAssert])#
offset
<integer> Number of bytes to skip before starting to read. Must satisfy:0 <= offset <= buf.length - 4
.noAssert
<boolean> Skipoffset
validation? Default:false
- Returns: <integer>
Reads a signed 32-bit integer from buf
at the specified offset
with
the specified endian format (readInt32BE()
returns big endian,
readInt32LE()
returns little endian).
Setting noAssert
to true
allows offset
to be beyond the end of buf
, but
the resulting behavior is undefined.
Integers read from a Buffer
are interpreted as two's complement signed values.
Examples:
const buf = Buffer.from([0, 0, 0, 5]);
// Prints: 5
console.log(buf.readInt32BE());
// Prints: 83886080
console.log(buf.readInt32LE());
// Throws an exception: RangeError: Index out of range
console.log(buf.readInt32LE(1));
buf.readIntBE(offset, byteLength[, noAssert])#
buf.readIntLE(offset, byteLength[, noAssert])#
offset
<integer> Number of bytes to skip before starting to read. Must satisfy:0 <= offset <= buf.length - byteLength
.byteLength
<integer> Number of bytes to read. Must satisfy:0 < byteLength <= 6
.noAssert
<boolean> Skipoffset
andbyteLength
validation? Default:false
.- Returns: <integer>
Reads byteLength
number of bytes from buf
at the specified offset
and interprets the result as a two's complement signed value. Supports up to 48
bits of accuracy.
Setting noAssert
to true
allows offset
to be beyond the end of buf
, but
the resulting behavior is undefined.
Examples:
const buf = Buffer.from([0x12, 0x34, 0x56, 0x78, 0x90, 0xab]);
// Prints: -546f87a9cbee
console.log(buf.readIntLE(0, 6).toString(16));
// Prints: 1234567890ab
console.log(buf.readIntBE(0, 6).toString(16));
// Throws an exception: RangeError: Index out of range
console.log(buf.readIntBE(1, 6).toString(16));
buf.readUInt8(offset[, noAssert])#
offset
<integer> Number of bytes to skip before starting to read. Must satisfy:0 <= offset <= buf.length - 1
.noAssert
<boolean> Skipoffset
validation? Default:false
- Returns: <integer>
Reads an unsigned 8-bit integer from buf
at the specified offset
.
Setting noAssert
to true
allows offset
to be beyond the end of buf
, but
the resulting behavior is undefined.
Examples:
const buf = Buffer.from([1, -2]);
// Prints: 1
console.log(buf.readUInt8(0));
// Prints: 254
console.log(buf.readUInt8(1));
// Throws an exception: RangeError: Index out of range
console.log(buf.readUInt8(2));
buf.readUInt16BE(offset[, noAssert])#
buf.readUInt16LE(offset[, noAssert])#
offset
<integer> Number of bytes to skip before starting to read. Must satisfy:0 <= offset <= buf.length - 2
.noAssert
<boolean> Skipoffset
validation? Default:false
- Returns: <integer>
Reads an unsigned 16-bit integer from buf
at the specified offset
with
specified endian format (readUInt16BE()
returns big endian, readUInt16LE()
returns little endian).
Setting noAssert
to true
allows offset
to be beyond the end of buf
, but
the resulting behavior is undefined.
Examples:
const buf = Buffer.from([0x12, 0x34, 0x56]);
// Prints: 1234
console.log(buf.readUInt16BE(0).toString(16));
// Prints: 3412
console.log(buf.readUInt16LE(0).toString(16));
// Prints: 3456
console.log(buf.readUInt16BE(1).toString(16));
// Prints: 5634
console.log(buf.readUInt16LE(1).toString(16));
// Throws an exception: RangeError: Index out of range
console.log(buf.readUInt16LE(2).toString(16));
buf.readUInt32BE(offset[, noAssert])#
buf.readUInt32LE(offset[, noAssert])#
offset
<integer> Number of bytes to skip before starting to read. Must satisfy:0 <= offset <= buf.length - 4
.noAssert
<boolean> Skipoffset
validation? Default:false
- Returns: <integer>
Reads an unsigned 32-bit integer from buf
at the specified offset
with
specified endian format (readUInt32BE()
returns big endian,
readUInt32LE()
returns little endian).
Setting noAssert
to true
allows offset
to be beyond the end of buf
, but
the resulting behavior is undefined.
Examples:
const buf = Buffer.from([0x12, 0x34, 0x56, 0x78]);
// Prints: 12345678
console.log(buf.readUInt32BE(0).toString(16));
// Prints: 78563412
console.log(buf.readUInt32LE(0).toString(16));
// Throws an exception: RangeError: Index out of range
console.log(buf.readUInt32LE(1).toString(16));
buf.readUIntBE(offset, byteLength[, noAssert])#
buf.readUIntLE(offset, byteLength[, noAssert])#
offset
<integer> Number of bytes to skip before starting to read. Must satisfy:0 <= offset <= buf.length - byteLength
.byteLength
<integer> Number of bytes to read. Must satisfy:0 < byteLength <= 6
.noAssert
<boolean> Skipoffset
andbyteLength
validation? Default:false
- Returns: <integer>
Reads byteLength
number of bytes from buf
at the specified offset
and interprets the result as an unsigned integer. Supports up to 48
bits of accuracy.
Setting noAssert
to true
allows offset
to be beyond the end of buf
, but
the resulting behavior is undefined.
Examples:
const buf = Buffer.from([0x12, 0x34, 0x56, 0x78, 0x90, 0xab]);
// Prints: 1234567890ab
console.log(buf.readUIntBE(0, 6).toString(16));
// Prints: ab9078563412
console.log(buf.readUIntLE(0, 6).toString(16));
// Throws an exception: RangeError: Index out of range
console.log(buf.readUIntBE(1, 6).toString(16));
buf.slice([start[, end]])#
start
<integer> Where the newBuffer
will start. Default:0
end
<integer> Where the newBuffer
will end (not inclusive). Default:buf.length
- Returns: <Buffer>
Returns a new Buffer
that references the same memory as the original, but
offset and cropped by the start
and end
indices.
Note that modifying the new Buffer
slice will modify the memory in the
original Buffer
because the allocated memory of the two objects overlap.
Example: Create a Buffer
with the ASCII alphabet, take a slice, and then modify
one byte from the original Buffer
const buf1 = Buffer.allocUnsafe(26);
for (let i = 0; i < 26; i++) {
// 97 is the decimal ASCII value for 'a'
buf1[i] = i + 97;
}
const buf2 = buf1.slice(0, 3);
// Prints: abc
console.log(buf2.toString('ascii', 0, buf2.length));
buf1[0] = 33;
// Prints: !bc
console.log(buf2.toString('ascii', 0, buf2.length));
Specifying negative indexes causes the slice to be generated relative to the
end of buf
rather than the beginning.
Examples:
const buf = Buffer.from('buffer');
// Prints: buffe
// (Equivalent to buf.slice(0, 5))
console.log(buf.slice(-6, -1).toString());
// Prints: buff
// (Equivalent to buf.slice(0, 4))
console.log(buf.slice(-6, -2).toString());
// Prints: uff
// (Equivalent to buf.slice(1, 4))
console.log(buf.slice(-5, -2).toString());
buf.swap16()#
- Returns: <Buffer> A reference to
buf
.
Interprets buf
as an array of unsigned 16-bit integers and swaps the byte-order
in-place. Throws a RangeError
if buf.length
is not a multiple of 2.
Examples:
const buf1 = Buffer.from([0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8]);
// Prints: <Buffer 01 02 03 04 05 06 07 08>
console.log(buf1);
buf1.swap16();
// Prints: <Buffer 02 01 04 03 06 05 08 07>
console.log(buf1);
const buf2 = Buffer.from([0x1, 0x2, 0x3]);
// Throws an exception: RangeError: Buffer size must be a multiple of 16-bits
buf2.swap16();
buf.swap32()#
- Returns: <Buffer> A reference to
buf
.
Interprets buf
as an array of unsigned 32-bit integers and swaps the byte-order
in-place. Throws a RangeError
if buf.length
is not a multiple of 4.
Examples:
const buf1 = Buffer.from([0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8]);
// Prints: <Buffer 01 02 03 04 05 06 07 08>
console.log(buf1);
buf1.swap32();
// Prints: <Buffer 04 03 02 01 08 07 06 05>
console.log(buf1);
const buf2 = Buffer.from([0x1, 0x2, 0x3]);
// Throws an exception: RangeError: Buffer size must be a multiple of 32-bits
buf2.swap32();
buf.swap64()#
- Returns: <Buffer> A reference to
buf
.
Interprets buf
as an array of 64-bit numbers and swaps the byte-order in-place.
Throws a RangeError
if buf.length
is not a multiple of 8.
Examples:
const buf1 = Buffer.from([0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8]);
// Prints: <Buffer 01 02 03 04 05 06 07 08>
console.log(buf1);
buf1.swap64();
// Prints: <Buffer 08 07 06 05 04 03 02 01>
console.log(buf1);
const buf2 = Buffer.from([0x1, 0x2, 0x3]);
// Throws an exception: RangeError: Buffer size must be a multiple of 64-bits
buf2.swap64();
Note that JavaScript cannot encode 64-bit integers. This method is intended for working with 64-bit floats.
buf.toString([encoding[, start[, end]]])#
encoding
<string> The character encoding to decode to. Default:'utf8'
start
<integer> The byte offset to start decoding at. Default:0
end
<integer> The byte offset to stop decoding at (not inclusive). Default:buf.length
- Returns: <string>
Decodes buf
to a string according to the specified character encoding in
encoding
. start
and end
may be passed to decode only a subset of buf
.
Examples:
const buf1 = Buffer.allocUnsafe(26);
for (let i = 0; i < 26; i++) {
// 97 is the decimal ASCII value for 'a'
buf1[i] = i + 97;
}
// Prints: abcdefghijklmnopqrstuvwxyz
console.log(buf1.toString('ascii'));
// Prints: abcde
console.log(buf1.toString('ascii', 0, 5));
const buf2 = Buffer.from('tést');
// Prints: 74c3a97374
console.log(buf2.toString('hex'));
// Prints: té
console.log(buf2.toString('utf8', 0, 3));
// Prints: té
console.log(buf2.toString(undefined, 0, 3));
buf.toJSON()#
- Returns: <Object>
Returns a JSON representation of buf
. JSON.stringify()
implicitly calls
this function when stringifying a Buffer
instance.
Example:
const buf = Buffer.from([0x1, 0x2, 0x3, 0x4, 0x5]);
const json = JSON.stringify(buf);
// Prints: {"type":"Buffer","data":[1,2,3,4,5]}
console.log(json);
const copy = JSON.parse(json, (key, value) => {
return value && value.type === 'Buffer' ?
Buffer.from(value.data) :
value;
});
// Prints: <Buffer 01 02 03 04 05>
console.log(copy);
buf.values()#
- Returns: <Iterator>
Creates and returns an iterator for buf
values (bytes). This function is
called automatically when a Buffer
is used in a for..of
statement.
Examples:
const buf = Buffer.from('buffer');
// Prints:
// 98
// 117
// 102
// 102
// 101
// 114
for (const value of buf.values()) {
console.log(value);
}
// Prints:
// 98
// 117
// 102
// 102
// 101
// 114
for (const value of buf) {
console.log(value);
}
buf.write(string[, offset[, length]][, encoding])#
string
<string> String to be written tobuf
.offset
<integer> Number of bytes to skip before starting to writestring
. Default:0
length
<integer> Number of bytes to write. Default:buf.length - offset
encoding
<string> The character encoding ofstring
. Default:'utf8'
- Returns: <integer> Number of bytes written.
Writes string
to buf
at offset
according to the character encoding in encoding
.
The length
parameter is the number of bytes to write. If buf
did not contain
enough space to fit the entire string, only a partial amount of string
will
be written. However, partially encoded characters will not be written.
Example:
const buf = Buffer.allocUnsafe(256);
const len = buf.write('\u00bd + \u00bc = \u00be', 0);
// Prints: 12 bytes: ½ + ¼ = ¾
console.log(`${len} bytes: ${buf.toString('utf8', 0, len)}`);
buf.writeDoubleBE(value, offset[, noAssert])#
buf.writeDoubleLE(value, offset[, noAssert])#
value
<number> Number to be written tobuf
.offset
<integer> Number of bytes to skip before starting to write. Must satisfy:0 <= offset <= buf.length - 8
.noAssert
<boolean> Skipvalue
andoffset
validation? Default:false
- Returns: <integer>
offset
plus the number of bytes written.
Writes value
to buf
at the specified offset
with specified endian
format (writeDoubleBE()
writes big endian, writeDoubleLE()
writes little
endian). value
should be a valid 64-bit double. Behavior is undefined when
value
is anything other than a 64-bit double.
Setting noAssert
to true
allows the encoded form of value
to extend beyond
the end of buf
, but the resulting behavior is undefined.
Examples:
const buf = Buffer.allocUnsafe(8);
buf.writeDoubleBE(0xdeadbeefcafebabe, 0);
// Prints: <Buffer 43 eb d5 b7 dd f9 5f d7>
console.log(buf);
buf.writeDoubleLE(0xdeadbeefcafebabe, 0);
// Prints: <Buffer d7 5f f9 dd b7 d5 eb 43>
console.log(buf);
buf.writeFloatBE(value, offset[, noAssert])#
buf.writeFloatLE(value, offset[, noAssert])#
value
<number> Number to be written tobuf
.offset
<integer> Number of bytes to skip before starting to write. Must satisfy:0 <= offset <= buf.length - 4
.noAssert
<boolean> Skipvalue
andoffset
validation? Default:false
- Returns: <integer>
offset
plus the number of bytes written.
Writes value
to buf
at the specified offset
with specified endian
format (writeFloatBE()
writes big endian, writeFloatLE()
writes little
endian). value
should be a valid 32-bit float. Behavior is undefined when
value
is anything other than a 32-bit float.
Setting noAssert
to true
allows the encoded form of value
to extend beyond
the end of buf
, but the resulting behavior is undefined.
Examples:
const buf = Buffer.allocUnsafe(4);
buf.writeFloatBE(0xcafebabe, 0);
// Prints: <Buffer 4f 4a fe bb>
console.log(buf);
buf.writeFloatLE(0xcafebabe, 0);
// Prints: <Buffer bb fe 4a 4f>
console.log(buf);
buf.writeInt8(value, offset[, noAssert])#
value
<integer> Number to be written tobuf
.offset
<integer> Number of bytes to skip before starting to write. Must satisfy:0 <= offset <= buf.length - 1
.noAssert
<boolean> Skipvalue
andoffset
validation? Default:false
- Returns: <integer>
offset
plus the number of bytes written.
Writes value
to buf
at the specified offset
. value
should be a valid
signed 8-bit integer. Behavior is undefined when value
is anything other than
a signed 8-bit integer.
Setting noAssert
to true
allows the encoded form of value
to extend beyond
the end of buf
, but the resulting behavior is undefined.
value
is interpreted and written as a two's complement signed integer.
Examples:
const buf = Buffer.allocUnsafe(2);
buf.writeInt8(2, 0);
buf.writeInt8(-2, 1);
// Prints: <Buffer 02 fe>
console.log(buf);
buf.writeInt16BE(value, offset[, noAssert])#
buf.writeInt16LE(value, offset[, noAssert])#
value
<integer> Number to be written tobuf
.offset
<integer> Number of bytes to skip before starting to write. Must satisfy:0 <= offset <= buf.length - 2
.noAssert
<boolean> Skipvalue
andoffset
validation? Default:false
- Returns: <integer>
offset
plus the number of bytes written.
Writes value
to buf
at the specified offset
with specified endian
format (writeInt16BE()
writes big endian, writeInt16LE()
writes little
endian). value
should be a valid signed 16-bit integer. Behavior is undefined
when value
is anything other than a signed 16-bit integer.
Setting noAssert
to true
allows the encoded form of value
to extend beyond
the end of buf
, but the resulting behavior is undefined.
value
is interpreted and written as a two's complement signed integer.
Examples:
const buf = Buffer.allocUnsafe(4);
buf.writeInt16BE(0x0102, 0);
buf.writeInt16LE(0x0304, 2);
// Prints: <Buffer 01 02 04 03>
console.log(buf);
buf.writeInt32BE(value, offset[, noAssert])#
buf.writeInt32LE(value, offset[, noAssert])#
value
<integer> Number to be written tobuf
.offset
<integer> Number of bytes to skip before starting to write. Must satisfy:0 <= offset <= buf.length - 4
.noAssert
<boolean> Skipvalue
andoffset
validation? Default:false
- Returns: <integer>
offset
plus the number of bytes written.
Writes value
to buf
at the specified offset
with specified endian
format (writeInt32BE()
writes big endian, writeInt32LE()
writes little
endian). value
should be a valid signed 32-bit integer. Behavior is undefined
when value
is anything other than a signed 32-bit integer.
Setting noAssert
to true
allows the encoded form of value
to extend beyond
the end of buf
, but the resulting behavior is undefined.
value
is interpreted and written as a two's complement signed integer.
Examples:
const buf = Buffer.allocUnsafe(8);
buf.writeInt32BE(0x01020304, 0);
buf.writeInt32LE(0x05060708, 4);
// Prints: <Buffer 01 02 03 04 08 07 06 05>
console.log(buf);
buf.writeIntBE(value, offset, byteLength[, noAssert])#
buf.writeIntLE(value, offset, byteLength[, noAssert])#
value
<integer> Number to be written tobuf
.offset
<integer> Number of bytes to skip before starting to write. Must satisfy:0 <= offset <= buf.length - byteLength
.byteLength
<integer> Number of bytes to write. Must satisfy:0 < byteLength <= 6
.noAssert
<boolean> Skipvalue
,offset
, andbyteLength
validation? Default:false
- Returns: <integer>
offset
plus the number of bytes written.
Writes byteLength
bytes of value
to buf
at the specified offset
.
Supports up to 48 bits of accuracy. Behavior is undefined when value
is
anything other than a signed integer.
Setting noAssert
to true
allows the encoded form of value
to extend beyond
the end of buf
, but the resulting behavior is undefined.
Examples:
const buf = Buffer.allocUnsafe(6);
buf.writeUIntBE(0x1234567890ab, 0, 6);
// Prints: <Buffer 12 34 56 78 90 ab>
console.log(buf);
buf.writeUIntLE(0x1234567890ab, 0, 6);
// Prints: <Buffer ab 90 78 56 34 12>
console.log(buf);
buf.writeUInt8(value, offset[, noAssert])#
value
<integer> Number to be written tobuf
.offset
<integer> Number of bytes to skip before starting to write. Must satisfy:0 <= offset <= buf.length - 1
.noAssert
<boolean> Skipvalue
andoffset
validation? Default:false
- Returns: <integer>
offset
plus the number of bytes written.
Writes value
to buf
at the specified offset
. value
should be a
valid unsigned 8-bit integer. Behavior is undefined when value
is anything
other than an unsigned 8-bit integer.
Setting noAssert
to true
allows the encoded form of value
to extend beyond
the end of buf
, but the resulting behavior is undefined.
Examples:
const buf = Buffer.allocUnsafe(4);
buf.writeUInt8(0x3, 0);
buf.writeUInt8(0x4, 1);
buf.writeUInt8(0x23, 2);
buf.writeUInt8(0x42, 3);
// Prints: <Buffer 03 04 23 42>
console.log(buf);
buf.writeUInt16BE(value, offset[, noAssert])#
buf.writeUInt16LE(value, offset[, noAssert])#
value
<integer> Number to be written tobuf
.offset
<integer> Number of bytes to skip before starting to write. Must satisfy:0 <= offset <= buf.length - 2
.noAssert
<boolean> Skipvalue
andoffset
validation? Default:false
- Returns: <integer>
offset
plus the number of bytes written.
Writes value
to buf
at the specified offset
with specified endian
format (writeUInt16BE()
writes big endian, writeUInt16LE()
writes little
endian). value
should be a valid unsigned 16-bit integer. Behavior is
undefined when value
is anything other than an unsigned 16-bit integer.
Setting noAssert
to true
allows the encoded form of value
to extend beyond
the end of buf
, but the resulting behavior is undefined.
Examples:
const buf = Buffer.allocUnsafe(4);
buf.writeUInt16BE(0xdead, 0);
buf.writeUInt16BE(0xbeef, 2);
// Prints: <Buffer de ad be ef>
console.log(buf);
buf.writeUInt16LE(0xdead, 0);
buf.writeUInt16LE(0xbeef, 2);
// Prints: <Buffer ad de ef be>
console.log(buf);
buf.writeUInt32BE(value, offset[, noAssert])#
buf.writeUInt32LE(value, offset[, noAssert])#
value
<integer> Number to be written tobuf
.offset
<integer> Number of bytes to skip before starting to write. Must satisfy:0 <= offset <= buf.length - 4
.noAssert
<boolean> Skipvalue
andoffset
validation? Default:false
- Returns: <integer>
offset
plus the number of bytes written.
Writes value
to buf
at the specified offset
with specified endian
format (writeUInt32BE()
writes big endian, writeUInt32LE()
writes little
endian). value
should be a valid unsigned 32-bit integer. Behavior is
undefined when value
is anything other than an unsigned 32-bit integer.
Setting noAssert
to true
allows the encoded form of value
to extend beyond
the end of buf
, but the resulting behavior is undefined.
Examples:
const buf = Buffer.allocUnsafe(4);
buf.writeUInt32BE(0xfeedface, 0);
// Prints: <Buffer fe ed fa ce>
console.log(buf);
buf.writeUInt32LE(0xfeedface, 0);
// Prints: <Buffer ce fa ed fe>
console.log(buf);
buf.writeUIntBE(value, offset, byteLength[, noAssert])#
buf.writeUIntLE(value, offset, byteLength[, noAssert])#
value
<integer> Number to be written tobuf
.offset
<integer> Number of bytes to skip before starting to write. Must satisfy:0 <= offset <= buf.length - byteLength
.byteLength
<integer> Number of bytes to write. Must satisfy:0 < byteLength <= 6
.noAssert
<boolean> Skipvalue
,offset
, andbyteLength
validation? Default:false
- Returns: <integer>
offset
plus the number of bytes written.
Writes byteLength
bytes of value
to buf
at the specified offset
.
Supports up to 48 bits of accuracy. Behavior is undefined when value
is
anything other than an unsigned integer.
Setting noAssert
to true
allows the encoded form of value
to extend beyond
the end of buf
, but the resulting behavior is undefined.
Examples:
const buf = Buffer.allocUnsafe(6);
buf.writeIntBE(0x1234567890ab, 0, 6);
// Prints: <Buffer 12 34 56 78 90 ab>
console.log(buf);
buf.writeIntLE(0x1234567890ab, 0, 6);
// Prints: <Buffer ab 90 78 56 34 12>
console.log(buf);
buffer.INSPECT_MAX_BYTES#
- <integer> Default:
50
Returns the maximum number of bytes that will be returned when
buf.inspect()
is called. This can be overridden by user modules. See
util.inspect()
for more details on buf.inspect()
behavior.
Note that this is a property on the buffer
module as returned by
require('buffer')
, not on the Buffer
global or a Buffer
instance.
buffer.kMaxLength#
- <integer> The largest size allowed for a single
Buffer
instance.
On 32-bit architectures, this value is (2^30)-1
(~1GB).
On 64-bit architectures, this value is (2^31)-1
(~2GB).
Class: SlowBuffer#
Buffer.allocUnsafeSlow()
instead.Returns an un-pooled Buffer
.
In order to avoid the garbage collection overhead of creating many individually
allocated Buffer
instances, by default allocations under 4KB are sliced from a
single larger allocated object. This approach improves both performance and memory
usage since v8 does not need to track and cleanup as many Persistent
objects.
In the case where a developer may need to retain a small chunk of memory from a
pool for an indeterminate amount of time, it may be appropriate to create an
un-pooled Buffer
instance using SlowBuffer
then copy out the relevant bits.
Example:
// Need to keep around a few small chunks of memory
const store = [];
socket.on('readable', () => {
const data = socket.read();
// Allocate for retained data
const sb = SlowBuffer(10);
// Copy the data into the new allocation
data.copy(sb, 0, 0, 10);
store.push(sb);
});
Use of SlowBuffer
should be used only as a last resort after a developer
has observed undue memory retention in their applications.
new SlowBuffer(size)#
Buffer.allocUnsafeSlow()
instead.size
<integer> The desired length of the newSlowBuffer
.
Allocates a new SlowBuffer
of size
bytes. The size
must be less than
or equal to the value of buffer.kMaxLength
. Otherwise, a RangeError
is
thrown. A zero-length Buffer
will be created if size <= 0
.
The underlying memory for SlowBuffer
instances is not initialized. The
contents of a newly created SlowBuffer
are unknown and could contain
sensitive data. Use buf.fill(0)
to initialize a SlowBuffer
to zeroes.
Example:
const SlowBuffer = require('buffer').SlowBuffer;
const buf = new SlowBuffer(5);
// Prints: (contents may vary): <Buffer 78 e0 82 02 01>
console.log(buf);
buf.fill(0);
// Prints: <Buffer 00 00 00 00 00>
console.log(buf);
Child Process#
The child_process
module provides the ability to spawn child processes in
a manner that is similar, but not identical, to popen(3). This capability
is primarily provided by the child_process.spawn()
function:
const spawn = require('child_process').spawn;
const ls = spawn('ls', ['-lh', '/usr']);
ls.stdout.on('data', (data) => {
console.log(`stdout: ${data}`);
});
ls.stderr.on('data', (data) => {
console.log(`stderr: ${data}`);
});
ls.on('close', (code) => {
console.log(`child process exited with code ${code}`);
});
By default, pipes for stdin
, stdout
and stderr
are established between
the parent Node.js process and the spawned child. It is possible to stream data
through these pipes in a non-blocking way. Note, however, that some programs
use line-buffered I/O internally. While that does not affect Node.js, it can
mean that data sent to the child process may not be immediately consumed.
The child_process.spawn()
method spawns the child process asynchronously,
without blocking the Node.js event loop. The child_process.spawnSync()
function provides equivalent functionality in a synchronous manner that blocks
the event loop until the spawned process either exits or is terminated.
For convenience, the child_process
module provides a handful of synchronous
and asynchronous alternatives to child_process.spawn()
and
child_process.spawnSync()
. Note that each of these alternatives are
implemented on top of child_process.spawn()
or child_process.spawnSync()
.
child_process.exec()
: spawns a shell and runs a command within that shell, passing thestdout
andstderr
to a callback function when complete.child_process.execFile()
: similar tochild_process.exec()
except that it spawns the command directly without first spawning a shell.child_process.fork()
: spawns a new Node.js process and invokes a specified module with an IPC communication channel established that allows sending messages between parent and child.child_process.execSync()
: a synchronous version ofchild_process.exec()
that will block the Node.js event loop.child_process.execFileSync()
: a synchronous version ofchild_process.execFile()
that will block the Node.js event loop.
For certain use cases, such as automating shell scripts, the synchronous counterparts may be more convenient. In many cases, however, the synchronous methods can have significant impact on performance due to stalling the event loop while spawned processes complete.
Asynchronous Process Creation#
The child_process.spawn()
, child_process.fork()
, child_process.exec()
,
and child_process.execFile()
methods all follow the idiomatic asynchronous
programming pattern typical of other Node.js APIs.
Each of the methods returns a ChildProcess
instance. These objects
implement the Node.js EventEmitter
API, allowing the parent process to
register listener functions that are called when certain events occur during
the life cycle of the child process.
The child_process.exec()
and child_process.execFile()
methods additionally
allow for an optional callback
function to be specified that is invoked
when the child process terminates.
Spawning .bat
and .cmd
files on Windows#
The importance of the distinction between child_process.exec()
and
child_process.execFile()
can vary based on platform. On Unix-type operating
systems (Unix, Linux, macOS) child_process.execFile()
can be more efficient
because it does not spawn a shell. On Windows, however, .bat
and .cmd
files are not executable on their own without a terminal, and therefore cannot
be launched using child_process.execFile()
. When running on Windows, .bat
and .cmd
files can be invoked using child_process.spawn()
with the shell
option set, with child_process.exec()
, or by spawning cmd.exe
and passing
the .bat
or .cmd
file as an argument (which is what the shell
option and
child_process.exec()
do). In any case, if the script filename contains
spaces it needs to be quoted.
// On Windows Only ...
const spawn = require('child_process').spawn;
const bat = spawn('cmd.exe', ['/c', 'my.bat']);
bat.stdout.on('data', (data) => {
console.log(data.toString());
});
bat.stderr.on('data', (data) => {
console.log(data.toString());
});
bat.on('exit', (code) => {
console.log(`Child exited with code ${code}`);
});
// OR...
const exec = require('child_process').exec;
exec('my.bat', (err, stdout, stderr) => {
if (err) {
console.error(err);
return;
}
console.log(stdout);
});
// Script with spaces in the filename:
const bat = spawn('"my script.cmd"', ['a', 'b'], { shell: true });
// or:
exec('"my script.cmd" a b', (err, stdout, stderr) => {
// ...
});
child_process.exec(command[, options][, callback])#
command
<string> The command to run, with space-separated arguments.options
<Object>cwd
<string> Current working directory of the child process.env
<Object> Environment key-value pairs.encoding
<string> Default:'utf8'
shell
<string> Shell to execute the command with. Default:'/bin/sh'
on UNIX,'cmd.exe'
on Windows. The shell should understand the-c
switch on UNIX or/s /c
on Windows. On Windows, command line parsing should be compatible withcmd.exe
.timeout
<number> Default:0
maxBuffer
<number> Largest amount of data (in bytes) allowed on stdout or stderr - if exceeded child process is killed. Default:200*1024
killSignal
<string> | <integer> Default:'SIGTERM'
uid
<number> Sets the user identity of the process (see setuid(2)).gid
<number> Sets the group identity of the process (see setgid(2)).
callback
<Function> Called with the output when process terminates.- Returns: <ChildProcess>
Spawns a shell then executes the command
within that shell, buffering any
generated output.
Note: Never pass unsanitised user input to this function. Any input containing shell metacharacters may be used to trigger arbitrary command execution.
const exec = require('child_process').exec;
exec('cat *.js bad_file | wc -l', (error, stdout, stderr) => {
if (error) {
console.error(`exec error: ${error}`);
return;
}
console.log(`stdout: ${stdout}`);
console.log(`stderr: ${stderr}`);
});
If a callback
function is provided, it is called with the arguments
(error, stdout, stderr)
. On success, error
will be null
. On error,
error
will be an instance of Error
. The error.code
property will be
the exit code of the child process while error.signal
will be set to the
signal that terminated the process. Any exit code other than 0
is considered
to be an error.
The stdout
and stderr
arguments passed to the callback will contain the
stdout and stderr output of the child process. By default, Node.js will decode
the output as UTF-8 and pass strings to the callback. The encoding
option
can be used to specify the character encoding used to decode the stdout and
stderr output. If encoding
is 'buffer'
, or an unrecognized character
encoding, Buffer
objects will be passed to the callback instead.
The options
argument may be passed as the second argument to customize how
the process is spawned. The default options are:
const defaults = {
encoding: 'utf8',
timeout: 0,
maxBuffer: 200 * 1024,
killSignal: 'SIGTERM',
cwd: null,
env: null
};
If timeout
is greater than 0
, the parent will send the signal
identified by the killSignal
property (the default is 'SIGTERM'
) if the
child runs longer than timeout
milliseconds.
Note: Unlike the exec(3) POSIX system call, child_process.exec()
does not
replace the existing process and uses a shell to execute the command.
child_process.execFile(file[, args][, options][, callback])#
file
<string> The name or path of the executable file to run.args
<string[]> List of string arguments.options
<Object>cwd
<string> Current working directory of the child process.env
<Object> Environment key-value pairs.encoding
<string> Default:'utf8'
timeout
<number> Default:0
maxBuffer
<number> Largest amount of data (in bytes) allowed on stdout or stderr - if exceeded child process is killed. Default::200*1024
killSignal
<string> | <integer> Default:'SIGTERM'
uid
<number> Sets the user identity of the process (see setuid(2)).gid
<number> Sets the group identity of the process (see setgid(2)).
callback
<Function> Called with the output when process terminates.- Returns: <ChildProcess>
The child_process.execFile()
function is similar to child_process.exec()
except that it does not spawn a shell. Rather, the specified executable file
is spawned directly as a new process making it slightly more efficient than
child_process.exec()
.
The same options as child_process.exec()
are supported. Since a shell is not
spawned, behaviors such as I/O redirection and file globbing are not supported.
const execFile = require('child_process').execFile;
const child = execFile('node', ['--version'], (error, stdout, stderr) => {
if (error) {
throw error;
}
console.log(stdout);
});
The stdout
and stderr
arguments passed to the callback will contain the
stdout and stderr output of the child process. By default, Node.js will decode
the output as UTF-8 and pass strings to the callback. The encoding
option
can be used to specify the character encoding used to decode the stdout and
stderr output. If encoding
is 'buffer'
, or an unrecognized character
encoding, Buffer
objects will be passed to the callback instead.
child_process.fork(modulePath[, args][, options])#
modulePath
<string> The module to run in the child.args
<Array> List of string arguments.options
<Object>cwd
<string> Current working directory of the child process.env
<Object> Environment key-value pairs.execPath
<string> Executable used to create the child process.execArgv
<Array> List of string arguments passed to the executable. Default:process.execArgv
silent
<boolean> Iftrue
, stdin, stdout, and stderr of the child will be piped to the parent, otherwise they will be inherited from the parent, see the'pipe'
and'inherit'
options forchild_process.spawn()
'sstdio
for more details. Default:false
stdio
<Array> Supports the array version ofchild_process.spawn()
'sstdio
option. When this option is provided, it overridessilent
. The array must contain exactly one item with value'ipc'
or an error will be thrown. For instance[0, 1, 2, 'ipc']
.uid
<number> Sets the user identity of the process (see setuid(2)).gid
<number> Sets the group identity of the process (see setgid(2)).
- Returns: <ChildProcess>
The child_process.fork()
method is a special case of
child_process.spawn()
used specifically to spawn new Node.js processes.
Like child_process.spawn()
, a ChildProcess
object is returned. The returned
ChildProcess
will have an additional communication channel built-in that
allows messages to be passed back and forth between the parent and child. See
subprocess.send()
for details.
It is important to keep in mind that spawned Node.js child processes are independent of the parent with exception of the IPC communication channel that is established between the two. Each process has its own memory, with their own V8 instances. Because of the additional resource allocations required, spawning a large number of child Node.js processes is not recommended.
By default, child_process.fork()
will spawn new Node.js instances using the
process.execPath
of the parent process. The execPath
property in the
options
object allows for an alternative execution path to be used.
Node.js processes launched with a custom execPath
will communicate with the
parent process using the file descriptor (fd) identified using the
environment variable NODE_CHANNEL_FD
on the child process. The input and
output on this fd is expected to be line delimited JSON objects.
Note: Unlike the fork(2) POSIX system call, child_process.fork()
does
not clone the current process.
Note: The shell
option available in child_process.spawn()
is not
supported by child_process.fork()
and will be ignored if set.
child_process.spawn(command[, args][, options])#
command
<string> The command to run.args
<Array> List of string arguments.options
<Object>cwd
<string> Current working directory of the child process.env
<Object> Environment key-value pairs.argv0
<string> Explicitly set the value ofargv[0]
sent to the child process. This will be set tocommand
if not specified.stdio
<Array> | <string> Child's stdio configuration (seeoptions.stdio
).detached
<boolean> Prepare child to run independently of its parent process. Specific behavior depends on the platform, seeoptions.detached
).uid
<number> Sets the user identity of the process (see setuid(2)).gid
<number> Sets the group identity of the process (see setgid(2)).shell
<boolean> | <string> Iftrue
, runscommand
inside of a shell. Uses'/bin/sh'
on UNIX, and'cmd.exe'
on Windows. A different shell can be specified as a string. The shell should understand the-c
switch on UNIX, or/s /c
on Windows. Default:false
(no shell).
- Returns: <ChildProcess>
The child_process.spawn()
method spawns a new process using the given
command
, with command line arguments in args
. If omitted, args
defaults
to an empty array.
Note: If the shell
option is enabled, do not pass unsanitised user input to
this function. Any input containing shell metacharacters may be used to
trigger arbitrary command execution.
A third argument may be used to specify additional options, with these defaults:
const defaults = {
cwd: undefined,
env: process.env
};
Use cwd
to specify the working directory from which the process is spawned.
If not given, the default is to inherit the current working directory.
Use env
to specify environment variables that will be visible to the new
process, the default is process.env
.
Example of running ls -lh /usr
, capturing stdout
, stderr
, and the
exit code:
const spawn = require('child_process').spawn;
const ls = spawn('ls', ['-lh', '/usr']);
ls.stdout.on('data', (data) => {
console.log(`stdout: ${data}`);
});
ls.stderr.on('data', (data) => {
console.log(`stderr: ${data}`);
});
ls.on('close', (code) => {
console.log(`child process exited with code ${code}`);
});
Example: A very elaborate way to run ps ax | grep ssh
const spawn = require('child_process').spawn;
const ps = spawn('ps', ['ax']);
const grep = spawn('grep', ['ssh']);
ps.stdout.on('data', (data) => {
grep.stdin.write(data);
});
ps.stderr.on('data', (data) => {
console.log(`ps stderr: ${data}`);
});
ps.on('close', (code) => {
if (code !== 0) {
console.log(`ps process exited with code ${code}`);
}
grep.stdin.end();
});
grep.stdout.on('data', (data) => {
console.log(data.toString());
});
grep.stderr.on('data', (data) => {
console.log(`grep stderr: ${data}`);
});
grep.on('close', (code) => {
if (code !== 0) {
console.log(`grep process exited with code ${code}`);
}
});
Example of checking for failed spawn
:
const spawn = require('child_process').spawn;
const subprocess = spawn('bad_command');
subprocess.on('error', (err) => {
console.log('Failed to start subprocess.');
});
Note: Certain platforms (macOS, Linux) will use the value of argv[0]
for the
process title while others (Windows, SunOS) will use command
.
Note: Node.js currently overwrites argv[0]
with process.execPath
on
startup, so process.argv[0]
in a Node.js child process will not match the
argv0
parameter passed to spawn
from the parent, retrieve it with the
process.argv0
property instead.
options.detached#
On Windows, setting options.detached
to true
makes it possible for the
child process to continue running after the parent exits. The child will have
its own console window. Once enabled for a child process, it cannot be
disabled.
On non-Windows platforms, if options.detached
is set to true
, the child
process will be made the leader of a new process group and session. Note that
child processes may continue running after the parent exits regardless of
whether they are detached or not. See setsid(2) for more information.
By default, the parent will wait for the detached child to exit. To prevent
the parent from waiting for a given subprocess
, use the subprocess.unref()
method. Doing so will cause the parent's event loop to not include the child in
its reference count, allowing the parent to exit independently of the child,
unless there is an established IPC channel between the child and parent.
When using the detached
option to start a long-running process, the process
will not stay running in the background after the parent exits unless it is
provided with a stdio
configuration that is not connected to the parent.
If the parent's stdio
is inherited, the child will remain attached to the
controlling terminal.
Example of a long-running process, by detaching and also ignoring its parent
stdio
file descriptors, in order to ignore the parent's termination:
const spawn = require('child_process').spawn;
const subprocess = spawn(process.argv[0], ['child_program.js'], {
detached: true,
stdio: 'ignore'
});
subprocess.unref();
Alternatively one can redirect the child process' output into files:
const fs = require('fs');
const spawn = require('child_process').spawn;
const out = fs.openSync('./out.log', 'a');
const err = fs.openSync('./out.log', 'a');
const subprocess = spawn('prg', [], {
detached: true,
stdio: [ 'ignore', out, err ]
});
subprocess.unref();
options.stdio#
The options.stdio
option is used to configure the pipes that are established
between the parent and child process. By default, the child's stdin, stdout,
and stderr are redirected to corresponding subprocess.stdin
,
subprocess.stdout
, and subprocess.stderr
streams on the
ChildProcess
object. This is equivalent to setting the options.stdio
equal to ['pipe', 'pipe', 'pipe']
.
For convenience, options.stdio
may be one of the following strings:
'pipe'
- equivalent to['pipe', 'pipe', 'pipe']
(the default)'ignore'
- equivalent to['ignore', 'ignore', 'ignore']
'inherit'
- equivalent to[process.stdin, process.stdout, process.stderr]
or[0,1,2]
Otherwise, the value of options.stdio
is an array where each index corresponds
to an fd in the child. The fds 0, 1, and 2 correspond to stdin, stdout,
and stderr, respectively. Additional fds can be specified to create additional
pipes between the parent and child. The value is one of the following:
'pipe'
- Create a pipe between the child process and the parent process. The parent end of the pipe is exposed to the parent as a property on thechild_process
object assubprocess.stdio[fd]
. Pipes created for fds 0 - 2 are also available assubprocess.stdin
,subprocess.stdout
andsubprocess.stderr
, respectively.'ipc'
- Create an IPC channel for passing messages/file descriptors between parent and child. AChildProcess
may have at most one IPC stdio file descriptor. Setting this option enables thesubprocess.send()
method. If the child writes JSON messages to this file descriptor, thesubprocess.on('message')
event handler will be triggered in the parent. If the child is a Node.js process, the presence of an IPC channel will enableprocess.send()
,process.disconnect()
,process.on('disconnect')
, andprocess.on('message')
within the child.'ignore'
- Instructs Node.js to ignore the fd in the child. While Node.js will always open fds 0 - 2 for the processes it spawns, setting the fd to'ignore'
will cause Node.js to open/dev/null
and attach it to the child's fd.- <Stream> object - Share a readable or writable stream that refers to a tty,
file, socket, or a pipe with the child process. The stream's underlying
file descriptor is duplicated in the child process to the fd that
corresponds to the index in the
stdio
array. Note that the stream must have an underlying descriptor (file streams do not until the'open'
event has occurred). - Positive integer - The integer value is interpreted as a file descriptor that is is currently open in the parent process. It is shared with the child process, similar to how <Stream> objects can be shared.
null
,undefined
- Use default value. For stdio fds 0, 1 and 2 (in other words, stdin, stdout, and stderr) a pipe is created. For fd 3 and up, the default is'ignore'
.
Example:
const spawn = require('child_process').spawn;
// Child will use parent's stdios
spawn('prg', [], { stdio: 'inherit' });
// Spawn child sharing only stderr
spawn('prg', [], { stdio: ['pipe', 'pipe', process.stderr] });
// Open an extra fd=4, to interact with programs presenting a
// startd-style interface.
spawn('prg', [], { stdio: ['pipe', null, null, null, 'pipe'] });
It is worth noting that when an IPC channel is established between the
parent and child processes, and the child is a Node.js process, the child
is launched with the IPC channel unreferenced (using unref()
) until the
child registers an event handler for the process.on('disconnect')
event
or the process.on('message')
event. This allows the child to exit
normally without the process being held open by the open IPC channel.
See also: child_process.exec()
and child_process.fork()
Synchronous Process Creation#
The child_process.spawnSync()
, child_process.execSync()
, and
child_process.execFileSync()
methods are synchronous and WILL block
the Node.js event loop, pausing execution of any additional code until the
spawned process exits.
Blocking calls like these are mostly useful for simplifying general purpose scripting tasks and for simplifying the loading/processing of application configuration at startup.
child_process.execFileSync(file[, args][, options])#
file
<string> The name or path of the executable file to run.args
<string[]> List of string arguments.options
<Object>cwd
<string> Current working directory of the child process.input
<string> | <Buffer> The value which will be passed as stdin to the spawned process.- supplying this value will override
stdio[0]
- supplying this value will override
stdio
<string> | <Array> Child's stdio configuration. Default:'pipe'
stderr
by default will be output to the parent process' stderr unlessstdio
is specified
env
<Object> Environment key-value pairs.uid
<number> Sets the user identity of the process (see setuid(2)).gid
<number> Sets the group identity of the process (see setgid(2)).timeout
<number> In milliseconds the maximum amount of time the process is allowed to run. Default:undefined
killSignal
<string> | <integer> The signal value to be used when the spawned process will be killed. Default:'SIGTERM'
maxBuffer
<number> Largest amount of data (in bytes) allowed on stdout or stderr - if exceeded child process is killed.encoding
<string> The encoding used for all stdio inputs and outputs. Default:'buffer'
- Returns: <Buffer> | <string> The stdout from the command.
The child_process.execFileSync()
method is generally identical to
child_process.execFile()
with the exception that the method will not return
until the child process has fully closed. When a timeout has been encountered
and killSignal
is sent, the method won't return until the process has
completely exited. Note that if the child process intercepts and handles
the SIGTERM
signal and does not exit, the parent process will still wait
until the child process has exited.
If the process times out, or has a non-zero exit code, this method will
throw an Error
that will include the full result of the underlying
child_process.spawnSync()
.
child_process.execSync(command[, options])#
command
<string> The command to run.options
<Object>cwd
<string> Current working directory of the child process.input
<string> | <Buffer> The value which will be passed as stdin to the spawned process.- supplying this value will override
stdio[0]
- supplying this value will override
stdio
<string> | <Array> Child's stdio configuration. Default:'pipe'
stderr
by default will be output to the parent process' stderr unlessstdio
is specified
env
<Object> Environment key-value pairs.shell
<string> Shell to execute the command with. Default:'/bin/sh'
on UNIX,'cmd.exe'
on Windows. The shell should understand the-c
switch on UNIX or/s /c
on Windows. On Windows, command line parsing should be compatible withcmd.exe
.uid
<number> Sets the user identity of the process. (see setuid(2)).gid
<number> Sets the group identity of the process. (see setgid(2)).timeout
<number> In milliseconds the maximum amount of time the process is allowed to run. Default:undefined
killSignal
<string> | <integer> The signal value to be used when the spawned process will be killed. Default:'SIGTERM'
maxBuffer
<number> Largest amount of data (in bytes) allowed on stdout or stderr - if exceeded child process is killed.encoding
<string> The encoding used for all stdio inputs and outputs. Default:'buffer'
- Returns: <Buffer> | <string> The stdout from the command.
The child_process.execSync()
method is generally identical to
child_process.exec()
with the exception that the method will not return until
the child process has fully closed. When a timeout has been encountered and
killSignal
is sent, the method won't return until the process has completely
exited. Note that if the child process intercepts and handles the SIGTERM
signal and doesn't exit, the parent process will wait until the child
process has exited.
If the process times out, or has a non-zero exit code, this method will
throw. The Error
object will contain the entire result from
child_process.spawnSync()
Note: Never pass unsanitised user input to this function. Any input containing shell metacharacters may be used to trigger arbitrary command execution.
child_process.spawnSync(command[, args][, options])#
command
<string> The command to run.args
<Array> List of string arguments.options
<Object>cwd
<string> Current working directory of the child process.input
<string> | <Buffer> The value which will be passed as stdin to the spawned process- supplying this value will override
stdio[0]
.
- supplying this value will override
stdio
<string> | <Array> Child's stdio configuration.env
<Object> Environment key-value pairs.uid
<number> Sets the user identity of the process (see setuid(2)).gid
<number> Sets the group identity of the process (see setgid(2)).timeout
<number> In milliseconds the maximum amount of time the process is allowed to run. Default:undefined
killSignal
<string> | <integer> The signal value to be used when the spawned process will be killed. Default:'SIGTERM'
maxBuffer
<number> Largest amount of data (in bytes) allowed on stdout or stderr - if exceeded child process is killed.encoding
<string> The encoding used for all stdio inputs and outputs. Default:'buffer'
shell
<boolean> | <string> Iftrue
, runscommand
inside of a shell. Uses'/bin/sh'
on UNIX, and'cmd.exe'
on Windows. A different shell can be specified as a string. The shell should understand the-c
switch on UNIX, or/s /c
on Windows. Default: tofalse
(no shell).
- Returns: <Object>
pid
<number> Pid of the child process.output
<Array> Array of results from stdio output.stdout
<Buffer> | <string> The contents ofoutput[1]
.stderr
<Buffer> | <string> The contents ofoutput[2]
.status
<number> The exit code of the child process.signal
<string> The signal used to kill the child process.error
<Error> The error object if the child process failed or timed out.
The child_process.spawnSync()
method is generally identical to
child_process.spawn()
with the exception that the function will not return
until the child process has fully closed. When a timeout has been encountered
and killSignal
is sent, the method won't return until the process has
completely exited. Note that if the process intercepts and handles the
SIGTERM
signal and doesn't exit, the parent process will wait until the child
process has exited.
Note: If the shell
option is enabled, do not pass unsanitised user input to
this function. Any input containing shell metacharacters may be used to
trigger arbitrary command execution.
Class: ChildProcess#
Instances of the ChildProcess
class are EventEmitters
that represent
spawned child processes.
Instances of ChildProcess
are not intended to be created directly. Rather,
use the child_process.spawn()
, child_process.exec()
,
child_process.execFile()
, or child_process.fork()
methods to create
instances of ChildProcess
.
Event: 'close'#
code
<number> The exit code if the child exited on its own.signal
<string> The signal by which the child process was terminated.
The 'close'
event is emitted when the stdio streams of a child process have
been closed. This is distinct from the 'exit'
event, since multiple
processes might share the same stdio streams.
Event: 'disconnect'#
The 'disconnect'
event is emitted after calling the
subprocess.disconnect()
method in parent process or
process.disconnect()
in child process. After disconnecting it is no longer
possible to send or receive messages, and the subprocess.connected
property is false
.
Event: 'error'#
err
<Error> The error.
The 'error'
event is emitted whenever:
- The process could not be spawned, or
- The process could not be killed, or
- Sending a message to the child process failed.
Note that the 'exit'
event may or may not fire after an error has occurred.
If you are listening to both the 'exit'
and 'error'
events, it is important
to guard against accidentally invoking handler functions multiple times.
See also subprocess.kill()
and subprocess.send()
.
Event: 'exit'#
code
<number> The exit code if the child exited on its own.signal
<string> The signal by which the child process was terminated.
The 'exit'
event is emitted after the child process ends. If the process
exited, code
is the final exit code of the process, otherwise null
. If the
process terminated due to receipt of a signal, signal
is the string name of
the signal, otherwise null
. One of the two will always be non-null.
Note that when the 'exit'
event is triggered, child process stdio streams
might still be open.
Also, note that Node.js establishes signal handlers for SIGINT
and
SIGTERM
and Node.js processes will not terminate immediately due to receipt
of those signals. Rather, Node.js will perform a sequence of cleanup actions
and then will re-raise the handled signal.
See waitpid(2).
Event: 'message'#
message
<Object> A parsed JSON object or primitive value.sendHandle
<Handle> Anet.Socket
ornet.Server
object, or undefined.
The 'message'
event is triggered when a child process uses process.send()
to send messages.
subprocess.connected#
- <boolean> Set to
false
aftersubprocess.disconnect()
is called.
The subprocess.connected
property indicates whether it is still possible to
send and receive messages from a child process. When subprocess.connected
is
false
, it is no longer possible to send or receive messages.
subprocess.disconnect()#
Closes the IPC channel between parent and child, allowing the child to exit
gracefully once there are no other connections keeping it alive. After calling
this method the subprocess.connected
and process.connected
properties in
both the parent and child (respectively) will be set to false
, and it will be
no longer possible to pass messages between the processes.
The 'disconnect'
event will be emitted when there are no messages in the
process of being received. This will most often be triggered immediately after
calling subprocess.disconnect()
.
Note that when the child process is a Node.js instance (e.g. spawned using
child_process.fork()
), the process.disconnect()
method can be invoked
within the child process to close the IPC channel as well.
subprocess.kill([signal])#
signal
<string>
The subprocess.kill()
method sends a signal to the child process. If no
argument is given, the process will be sent the 'SIGTERM'
signal. See
signal(7) for a list of available signals.
const spawn = require('child_process').spawn;
const grep = spawn('grep', ['ssh']);
grep.on('close', (code, signal) => {
console.log(
`child process terminated due to receipt of signal ${signal}`);
});
// Send SIGHUP to process
grep.kill('SIGHUP');
The ChildProcess
object may emit an 'error'
event if the signal cannot be
delivered. Sending a signal to a child process that has already exited is not
an error but may have unforeseen consequences. Specifically, if the process
identifier (PID) has been reassigned to another process, the signal will be
delivered to that process instead which can have unexpected results.
Note that while the function is called kill
, the signal delivered to the
child process may not actually terminate the process.
See kill(2) for reference.
Also note: on Linux, child processes of child processes will not be terminated
when attempting to kill their parent. This is likely to happen when running a
new process in a shell or with use of the shell
option of ChildProcess
, such
as in this example:
'use strict';
const spawn = require('child_process').spawn;
const subprocess = spawn(
'sh',
[
'-c',
`node -e "setInterval(() => {
console.log(process.pid, 'is alive')
}, 500);"`
], {
stdio: ['inherit', 'inherit', 'inherit']
}
);
setTimeout(() => {
subprocess.kill(); // does not terminate the node process in the shell
}, 2000);
subprocess.killed#
- <boolean> Set to
true
aftersubprocess.kill()
is used to successfully send a signal to the child process.
The subprocess.killed
property indicates whether the child process
successfully received a signal from subprocess.kill()
. The killed
property
does not indicate that the child process has been terminated.
subprocess.pid#
- <number> Integer
Returns the process identifier (PID) of the child process.
Example:
const spawn = require('child_process').spawn;
const grep = spawn('grep', ['ssh']);
console.log(`Spawned child pid: ${grep.pid}`);
grep.stdin.end();
subprocess.send(message[, sendHandle[, options]][, callback])#
message
<Object>sendHandle
<Handle>options
<Object>callback
<Function>- Returns: <boolean>
When an IPC channel has been established between the parent and child (
i.e. when using child_process.fork()
), the subprocess.send()
method can
be used to send messages to the child process. When the child process is a
Node.js instance, these messages can be received via the
process.on('message')
event.
For example, in the parent script:
const cp = require('child_process');
const n = cp.fork(`${__dirname}/sub.js`);
n.on('message', (m) => {
console.log('PARENT got message:', m);
});
n.send({ hello: 'world' });
And then the child script, 'sub.js'
might look like this:
process.on('message', (m) => {
console.log('CHILD got message:', m);
});
process.send({ foo: 'bar' });
Child Node.js processes will have a process.send()
method of their own that
allows the child to send messages back to the parent.
There is a special case when sending a {cmd: 'NODE_foo'}
message. Messages
containing a NODE_
prefix in the cmd
property are reserved for use within
Node.js core and will not be emitted in the child's process.on('message')
event. Rather, such messages are emitted using the
process.on('internalMessage')
event and are consumed internally by Node.js.
Applications should avoid using such messages or listening for
'internalMessage'
events as it is subject to change without notice.
The optional sendHandle
argument that may be passed to subprocess.send()
is
for passing a TCP server or socket object to the child process. The child will
receive the object as the second argument passed to the callback function
registered on the process.on('message')
event. Any data that is received
and buffered in the socket will not be sent to the child.
The options
argument, if present, is an object used to parameterize the
sending of certain types of handles. options
supports the following
properties:
keepOpen
- A Boolean value that can be used when passing instances ofnet.Socket
. Whentrue
, the socket is kept open in the sending process. Defaults tofalse
.
The optional callback
is a function that is invoked after the message is
sent but before the child may have received it. The function is called with a
single argument: null
on success, or an Error
object on failure.
If no callback
function is provided and the message cannot be sent, an
'error'
event will be emitted by the ChildProcess
object. This can happen,
for instance, when the child process has already exited.
subprocess.send()
will return false
if the channel has closed or when the
backlog of unsent messages exceeds a threshold that makes it unwise to send
more. Otherwise, the method returns true
. The callback
function can be
used to implement flow control.
Example: sending a server object#
The sendHandle
argument can be used, for instance, to pass the handle of
a TCP server object to the child process as illustrated in the example below:
const subprocess = require('child_process').fork('subprocess.js');
// Open up the server object and send the handle.
const server = require('net').createServer();
server.on('connection', (socket) => {
socket.end('handled by parent');
});
server.listen(1337, () => {
subprocess.send('server', server);
});
The child would then receive the server object as:
process.on('message', (m, server) => {
if (m === 'server') {
server.on('connection', (socket) => {
socket.end('handled by child');
});
}
});
Once the server is now shared between the parent and child, some connections can be handled by the parent and some by the child.
While the example above uses a server created using the net
module, dgram
module servers use exactly the same workflow with the exceptions of listening on
a 'message'
event instead of 'connection'
and using server.bind()
instead of
server.listen()
. This is, however, currently only supported on UNIX platforms.
Example: sending a socket object#
Similarly, the sendHandler
argument can be used to pass the handle of a
socket to the child process. The example below spawns two children that each
handle connections with "normal" or "special" priority:
const { fork } = require('child_process');
const normal = fork('subprocess.js', ['normal']);
const special = fork('subprocess.js', ['special']);
// Open up the server and send sockets to child. Use pauseOnConnect to prevent
// the sockets from being read before they are sent to the child process.
const server = require('net').createServer({ pauseOnConnect: true });
server.on('connection', (socket) => {
// If this is special priority
if (socket.remoteAddress === '74.125.127.100') {
special.send('socket', socket);
return;
}
// This is normal priority
normal.send('socket', socket);
});
server.listen(1337);
The subprocess.js
would receive the socket handle as the second argument
passed to the event callback function:
process.on('message', (m, socket) => {
if (m === 'socket') {
if (socket) {
// Check that the client socket exists.
// It is possible for the socket to be closed between the time it is
// sent and the time it is received in the child process.
socket.end(`Request handled with ${process.argv[2]} priority`);
}
}
});
Once a socket has been passed to a child, the parent is no longer capable of
tracking when the socket is destroyed. To indicate this, the .connections
property becomes null
. It is recommended not to use .maxConnections
when
this occurs.
It is also recommended that any 'message'
handlers in the child process
verify that socket
exists, as the connection may have been closed during the
time it takes to send the connection to the child.
Note: this function uses JSON.stringify()
internally to serialize the
message
.
subprocess.stderr#
A Readable Stream
that represents the child process's stderr
.
If the child was spawned with stdio[2]
set to anything other than 'pipe'
,
then this will be null
.
subprocess.stderr
is an alias for subprocess.stdio[2]
. Both properties will
refer to the same value.
subprocess.stdin#
A Writable Stream
that represents the child process's stdin
.
Note that if a child process waits to read all of its input, the child will not
continue until this stream has been closed via end()
.
If the child was spawned with stdio[0]
set to anything other than 'pipe'
,
then this will be null
.
subprocess.stdin
is an alias for subprocess.stdio[0]
. Both properties will
refer to the same value.
subprocess.stdio#
A sparse array of pipes to the child process, corresponding with positions in
the stdio
option passed to child_process.spawn()
that have been set
to the value 'pipe'
. Note that subprocess.stdio[0]
, subprocess.stdio[1]
,
and subprocess.stdio[2]
are also available as subprocess.stdin
,
subprocess.stdout
, and subprocess.stderr
, respectively.
In the following example, only the child's fd 1
(stdout) is configured as a
pipe, so only the parent's subprocess.stdio[1]
is a stream, all other values
in the array are null
.
const assert = require('assert');
const fs = require('fs');
const child_process = require('child_process');
const subprocess = child_process.spawn('ls', {
stdio: [
0, // Use parent's stdin for child
'pipe', // Pipe child's stdout to parent
fs.openSync('err.out', 'w') // Direct child's stderr to a file
]
});
assert.strictEqual(subprocess.stdio[0], null);
assert.strictEqual(subprocess.stdio[0], subprocess.stdin);
assert(subprocess.stdout);
assert.strictEqual(subprocess.stdio[1], subprocess.stdout);
assert.strictEqual(subprocess.stdio[2], null);
assert.strictEqual(subprocess.stdio[2], subprocess.stderr);
subprocess.stdout#
A Readable Stream
that represents the child process's stdout
.
If the child was spawned with stdio[1]
set to anything other than 'pipe'
,
then this will be null
.
subprocess.stdout
is an alias for subprocess.stdio[1]
. Both properties will
refer to the same value.
maxBuffer
and Unicode#
The maxBuffer
option specifies the largest number of bytes allowed on stdout
or stderr
. If this value is exceeded, then the child process is terminated.
This impacts output that includes multibyte character encodings such as UTF-8 or
UTF-16. For instance, console.log('中文测试')
will send 13 UTF-8 encoded bytes
to stdout
although there are only 4 characters.
Cluster#
A single instance of Node.js runs in a single thread. To take advantage of multi-core systems, the user will sometimes want to launch a cluster of Node.js processes to handle the load.
The cluster module allows you to easily create child processes that all share server ports.
const cluster = require('cluster');
const http = require('http');
const numCPUs = require('os').cpus().length;
if (cluster.isMaster) {
console.log(`Master ${process.pid} is running`);
// Fork workers.
for (let i = 0; i < numCPUs; i++) {
cluster.fork();
}
cluster.on('exit', (worker, code, signal) => {
console.log(`worker ${worker.process.pid} died`);
});
} else {
// Workers can share any TCP connection
// In this case it is an HTTP server
http.createServer((req, res) => {
res.writeHead(200);
res.end('hello world\n');
}).listen(8000);
console.log(`Worker ${process.pid} started`);
}
Running Node.js will now share port 8000 between the workers:
$ node server.js
Master 3596 is running
Worker 4324 started
Worker 4520 started
Worker 6056 started
Worker 5644 started
Please note that on Windows, it is not yet possible to set up a named pipe server in a worker.
How It Works#
The worker processes are spawned using the child_process.fork()
method,
so that they can communicate with the parent via IPC and pass server
handles back and forth.
The cluster module supports two methods of distributing incoming connections.
The first one (and the default one on all platforms except Windows), is the round-robin approach, where the master process listens on a port, accepts new connections and distributes them across the workers in a round-robin fashion, with some built-in smarts to avoid overloading a worker process.
The second approach is where the master process creates the listen socket and sends it to interested workers. The workers then accept incoming connections directly.
The second approach should, in theory, give the best performance. In practice however, distribution tends to be very unbalanced due to operating system scheduler vagaries. Loads have been observed where over 70% of all connections ended up in just two processes, out of a total of eight.
Because server.listen()
hands off most of the work to the master
process, there are three cases where the behavior between a normal
Node.js process and a cluster worker differs:
server.listen({fd: 7})
Because the message is passed to the master, file descriptor 7 in the parent will be listened on, and the handle passed to the worker, rather than listening to the worker's idea of what the number 7 file descriptor references.server.listen(handle)
Listening on handles explicitly will cause the worker to use the supplied handle, rather than talk to the master process. If the worker already has the handle, then it's presumed that you know what you are doing.server.listen(0)
Normally, this will cause servers to listen on a random port. However, in a cluster, each worker will receive the same "random" port each time they dolisten(0)
. In essence, the port is random the first time, but predictable thereafter. If you want to listen on a unique port, generate a port number based on the cluster worker ID.
There is no routing logic in Node.js, or in your program, and no shared state between the workers. Therefore, it is important to design your program such that it does not rely too heavily on in-memory data objects for things like sessions and login.
Because workers are all separate processes, they can be killed or re-spawned depending on your program's needs, without affecting other workers. As long as there are some workers still alive, the server will continue to accept connections. If no workers are alive, existing connections will be dropped and new connections will be refused. Node.js does not automatically manage the number of workers for you, however. It is your responsibility to manage the worker pool for your application's needs.
Although a primary use case for the cluster
module is networking, it can
also be used for other use cases requiring worker processes.
Class: Worker#
A Worker object contains all public information and method about a worker.
In the master it can be obtained using cluster.workers
. In a worker
it can be obtained using cluster.worker
.
Event: 'disconnect'#
Similar to the cluster.on('disconnect')
event, but specific to this worker.
cluster.fork().on('disconnect', () => {
// Worker has disconnected
});
Event: 'error'#
This event is the same as the one provided by child_process.fork()
.
In a worker you can also use process.on('error')
.
Event: 'exit'#
code
<number> The exit code, if it exited normally.signal
<string> The name of the signal (e.g.'SIGHUP'
) that caused the process to be killed.
Similar to the cluster.on('exit')
event, but specific to this worker.
const worker = cluster.fork();
worker.on('exit', (code, signal) => {
if (signal) {
console.log(`worker was killed by signal: ${signal}`);
} else if (code !== 0) {
console.log(`worker exited with error code: ${code}`);
} else {
console.log('worker success!');
}
});
Event: 'listening'#
address
<Object>
Similar to the cluster.on('listening')
event, but specific to this worker.
cluster.fork().on('listening', (address) => {
// Worker is listening
});
It is not emitted in the worker.
Event: 'message'#
message
<Object>handle
<undefined> | <Object>
Similar to the cluster.on('message')
event, but specific to this worker. In a
worker you can also use process.on('message')
.
As an example, here is a cluster that keeps count of the number of requests in the master process using the message system:
const cluster = require('cluster');
const http = require('http');
if (cluster.isMaster) {
// Keep track of http requests
let numReqs = 0;
setInterval(() => {
console.log(`numReqs = ${numReqs}`);
}, 1000);
// Count requests
function messageHandler(msg) {
if (msg.cmd && msg.cmd === 'notifyRequest') {
numReqs += 1;
}
}
// Start workers and listen for messages containing notifyRequest
const numCPUs = require('os').cpus().length;
for (let i = 0; i < numCPUs; i++) {
cluster.fork();
}
for (const id in cluster.workers) {
cluster.workers[id].on('message', messageHandler);
}
} else {
// Worker processes have a http server.
http.Server((req, res) => {
res.writeHead(200);
res.end('hello world\n');
// notify master about the request
process.send({ cmd: 'notifyRequest' });
}).listen(8000);
}
Event: 'online'#
Similar to the cluster.on('online')
event, but specific to this worker.
cluster.fork().on('online', () => {
// Worker is online
});
It is not emitted in the worker.
worker.disconnect()#
- Returns: <Worker> A reference to
worker
.
In a worker, this function will close all servers, wait for the 'close'
event on
those servers, and then disconnect the IPC channel.
In the master, an internal message is sent to the worker causing it to call
.disconnect()
on itself.
Causes .exitedAfterDisconnect
to be set.
Note that after a server is closed, it will no longer accept new connections,
but connections may be accepted by any other listening worker. Existing
connections will be allowed to close as usual. When no more connections exist,
see server.close()
, the IPC channel to the worker will close allowing it to
die gracefully.
The above applies only to server connections, client connections are not automatically closed by workers, and disconnect does not wait for them to close before exiting.
Note that in a worker, process.disconnect
exists, but it is not this function,
it is disconnect
.
Because long living server connections may block workers from disconnecting, it
may be useful to send a message, so application specific actions may be taken to
close them. It also may be useful to implement a timeout, killing a worker if
the 'disconnect'
event has not been emitted after some time.
if (cluster.isMaster) {
const worker = cluster.fork();
let timeout;
worker.on('listening', (address) => {
worker.send('shutdown');
worker.disconnect();
timeout = setTimeout(() => {
worker.kill();
}, 2000);
});
worker.on('disconnect', () => {
clearTimeout(timeout);
});
} else if (cluster.isWorker) {
const net = require('net');
const server = net.createServer((socket) => {
// connections never end
});
server.listen(8000);
process.on('message', (msg) => {
if (msg === 'shutdown') {
// initiate graceful close of any connections to server
}
});
}
worker.exitedAfterDisconnect#
Set by calling .kill()
or .disconnect()
. Until then, it is undefined
.
The boolean worker.exitedAfterDisconnect
lets you distinguish between voluntary
and accidental exit, the master may choose not to respawn a worker based on
this value.
cluster.on('exit', (worker, code, signal) => {
if (worker.exitedAfterDisconnect === true) {
console.log('Oh, it was just voluntary – no need to worry');
}
});
// kill worker
worker.kill();
worker.id#
Each new worker is given its own unique id, this id is stored in the
id
.
While a worker is alive, this is the key that indexes it in cluster.workers
worker.isConnected()#
This function returns true
if the worker is connected to its master via its IPC
channel, false
otherwise. A worker is connected to its master after it's been
created. It is disconnected after the 'disconnect'
event is emitted.
worker.isDead()#
This function returns true
if the worker's process has terminated (either
because of exiting or being signaled). Otherwise, it returns false
.
worker.kill([signal='SIGTERM'])#
signal
<string> Name of the kill signal to send to the worker process.
This function will kill the worker. In the master, it does this by disconnecting
the worker.process
, and once disconnected, killing with signal
. In the
worker, it does it by disconnecting the channel, and then exiting with code 0
.
Causes .exitedAfterDisconnect
to be set.
This method is aliased as worker.destroy()
for backwards compatibility.
Note that in a worker, process.kill()
exists, but it is not this function,
it is kill
.
worker.process#
All workers are created using child_process.fork()
, the returned object
from this function is stored as .process
. In a worker, the global process
is stored.
See: Child Process module
Note that workers will call process.exit(0)
if the 'disconnect'
event occurs
on process
and .exitedAfterDisconnect
is not true
. This protects against
accidental disconnection.
worker.send(message[, sendHandle][, callback])#
message
<Object>sendHandle
<Handle>callback
<Function>- Returns: <boolean>
Send a message to a worker or master, optionally with a handle.
In the master this sends a message to a specific worker. It is identical to
ChildProcess.send()
.
In a worker this sends a message to the master. It is identical to
process.send()
.
This example will echo back all messages from the master:
if (cluster.isMaster) {
const worker = cluster.fork();
worker.send('hi there');
} else if (cluster.isWorker) {
process.on('message', (msg) => {
process.send(msg);
});
}
worker.suicide#
worker.exitedAfterDisconnect
instead.An alias to worker.exitedAfterDisconnect
.
Set by calling .kill()
or .disconnect()
. Until then, it is undefined
.
The boolean worker.suicide
lets you distinguish between voluntary
and accidental exit, the master may choose not to respawn a worker based on
this value.
cluster.on('exit', (worker, code, signal) => {
if (worker.suicide === true) {
console.log('Oh, it was just voluntary – no need to worry');
}
});
// kill worker
worker.kill();
This API only exists for backwards compatibility and will be removed in the future.
Event: 'disconnect'#
worker
<cluster.Worker>
Emitted after the worker IPC channel has disconnected. This can occur when a worker exits gracefully, is killed, or is disconnected manually (such as with worker.disconnect()).
There may be a delay between the 'disconnect'
and 'exit'
events. These events
can be used to detect if the process is stuck in a cleanup or if there are
long-living connections.
cluster.on('disconnect', (worker) => {
console.log(`The worker #${worker.id} has disconnected`);
});
Event: 'exit'#
worker
<cluster.Worker>code
<number> The exit code, if it exited normally.signal
<string> The name of the signal (e.g.'SIGHUP'
) that caused the process to be killed.
When any of the workers die the cluster module will emit the 'exit'
event.
This can be used to restart the worker by calling .fork()
again.
cluster.on(
'exit',
(worker, code, signal) => {
console.log('worker %d died (%s). restarting...',
worker.process.pid, signal || code);
cluster.fork();
}
);
See child_process event: 'exit'.
Event: 'fork'#
worker
<cluster.Worker>
When a new worker is forked the cluster module will emit a 'fork'
event.
This can be used to log worker activity, and create your own timeout.
const timeouts = [];
function errorMsg() {
console.error('Something must be wrong with the connection ...');
}
cluster.on('fork', (worker) => {
timeouts[worker.id] = setTimeout(errorMsg, 2000);
});
cluster.on('listening', (worker, address) => {
clearTimeout(timeouts[worker.id]);
});
cluster.on('exit', (worker, code, signal) => {
clearTimeout(timeouts[worker.id]);
errorMsg();
});
Event: 'listening'#
worker
<cluster.Worker>address
<Object>
After calling listen()
from a worker, when the 'listening'
event is emitted on
the server, a 'listening'
event will also be emitted on cluster
in the master.
The event handler is executed with two arguments, the worker
contains the worker
object and the address
object contains the following connection properties:
address
, port
and addressType
. This is very useful if the worker is listening
on more than one address.
cluster.on('listening', (worker, address) => {
console.log(
`A worker is now connected to ${address.address}:${address.port}`);
});
The addressType
is one of:
4
(TCPv4)6
(TCPv6)-1
(unix domain socket)"udp4"
or"udp6"
(UDP v4 or v6)
Event: 'message'#
worker
<cluster.Worker>message
<Object>handle
<undefined> | <Object>
Emitted when the cluster master receives a message from any worker.
See child_process event: 'message'.
Before Node.js v6.0, this event emitted only the message and the handle, but not the worker object, contrary to what the documentation stated.
If you need to support older versions and don't need the worker object, you can work around the discrepancy by checking the number of arguments:
cluster.on('message', (worker, message, handle) => {
if (arguments.length === 2) {
handle = message;
message = worker;
worker = undefined;
}
// ...
});
Event: 'online'#
worker
<cluster.Worker>
After forking a new worker, the worker should respond with an online message.
When the master receives an online message it will emit this event.
The difference between 'fork'
and 'online'
is that fork is emitted when the
master forks a worker, and 'online' is emitted when the worker is running.
cluster.on('online', (worker) => {
console.log('Yay, the worker responded after it was forked');
});
Event: 'setup'#
settings
<Object>
Emitted every time .setupMaster()
is called.
The settings
object is the cluster.settings
object at the time
.setupMaster()
was called and is advisory only, since multiple calls to
.setupMaster()
can be made in a single tick.
If accuracy is important, use cluster.settings
.
cluster.disconnect([callback])#
callback
<Function> Called when all workers are disconnected and handles are closed.
Calls .disconnect()
on each worker in cluster.workers
.
When they are disconnected all internal handles will be closed, allowing the master process to die gracefully if no other event is waiting.
The method takes an optional callback argument which will be called when finished.
This can only be called from the master process.
cluster.fork([env])#
env
<Object> Key/value pairs to add to worker process environment.- Returns: <cluster.Worker>
Spawn a new worker process.
This can only be called from the master process.
cluster.isMaster#
True if the process is a master. This is determined
by the process.env.NODE_UNIQUE_ID
. If process.env.NODE_UNIQUE_ID
is
undefined, then isMaster
is true
.
cluster.isWorker#
True if the process is not a master (it is the negation of cluster.isMaster
).
cluster.schedulingPolicy#
The scheduling policy, either cluster.SCHED_RR
for round-robin or
cluster.SCHED_NONE
to leave it to the operating system. This is a
global setting and effectively frozen once you spawn the first worker
or call cluster.setupMaster()
, whatever comes first.
SCHED_RR
is the default on all operating systems except Windows.
Windows will change to SCHED_RR
once libuv is able to effectively
distribute IOCP handles without incurring a large performance hit.
cluster.schedulingPolicy
can also be set through the
NODE_CLUSTER_SCHED_POLICY
environment variable. Valid
values are "rr"
and "none"
.
cluster.settings#
- <Object>
execArgv
<Array> list of string arguments passed to the Node.js executable. Default:process.execArgv
exec
<string> file path to worker file. Default:process.argv[1]
args
<Array> string arguments passed to worker. Default::process.argv.slice(2)
silent
<boolean> whether or not to send output to parent's stdio. Default:false
stdio
<Array> Configures the stdio of forked processes. Because the cluster module relies on IPC to function, this configuration must contain an'ipc'
entry. When this option is provided, it overridessilent
.uid
<number> Sets the user identity of the process. (see setuid(2))gid
<number> Sets the group identity of the process. (see setgid(2))
After calling .setupMaster()
(or .fork()
) this settings object will contain
the settings, including the default values.
This object is not supposed to be changed or set manually, by you.
cluster.setupMaster([settings])#
settings
<Object>exec
<string> file path to worker file. Default:process.argv[1]
args
<Array> string arguments passed to worker. Default::process.argv.slice(2)
silent
<boolean> whether or not to send output to parent's stdio. Default:false
stdio
<Array> Configures the stdio of forked processes. When this option is provided, it overridessilent
.
setupMaster
is used to change the default 'fork' behavior. Once called,
the settings will be present in cluster.settings
.
Note that:
- any settings changes only affect future calls to
.fork()
and have no effect on workers that are already running - The only attribute of a worker that cannot be set via
.setupMaster()
is theenv
passed to.fork()
- the defaults above apply to the first call only, the defaults for later
calls is the current value at the time of
cluster.setupMaster()
is called
Example:
const cluster = require('cluster');
cluster.setupMaster({
exec: 'worker.js',
args: ['--use', 'https'],
silent: true
});
cluster.fork(); // https worker
cluster.setupMaster({
exec: 'worker.js',
args: ['--use', 'http']
});
cluster.fork(); // http worker
This can only be called from the master process.
cluster.worker#
A reference to the current worker object. Not available in the master process.
const cluster = require('cluster');
if (cluster.isMaster) {
console.log('I am master');
cluster.fork();
cluster.fork();
} else if (cluster.isWorker) {
console.log(`I am worker #${cluster.worker.id}`);
}
cluster.workers#
A hash that stores the active worker objects, keyed by id
field. Makes it
easy to loop through all the workers. It is only available in the master
process.
A worker is removed from cluster.workers after the worker has disconnected and
exited. The order between these two events cannot be determined in advance.
However, it is guaranteed that the removal from the cluster.workers list happens
before last 'disconnect'
or 'exit'
event is emitted.
// Go through all workers
function eachWorker(callback) {
for (const id in cluster.workers) {
callback(cluster.workers[id]);
}
}
eachWorker((worker) => {
worker.send('big announcement to all workers');
});
Should you wish to reference a worker over a communication channel, using the worker's unique id is the easiest way to find the worker.
socket.on('data', (id) => {
const worker = cluster.workers[id];
});
Command Line Options#
Node.js comes with a variety of CLI options. These options expose built-in debugging, multiple ways to execute scripts, and other helpful runtime options.
To view this documentation as a manual page in your terminal, run man node
.
Synopsis#
node [options] [v8 options] [script.js | -e "script"] [--] [arguments]
node debug [script.js | -e "script" | <host>:<port>] …
node --v8-options
Execute without arguments to start the REPL.
For more info about node debug
, please see the debugger documentation.
Options#
-v
, --version
#
Print node's version.
-h
, --help
#
Print node command line options. The output of this option is less detailed than this document.
-e
, --eval "script"
#
Evaluate the following argument as JavaScript. The modules which are
predefined in the REPL can also be used in script
.
Note: On Windows, using cmd.exe
a single quote will not work correctly
because it only recognizes double "
for quoting. In Powershell or
Git bash, both '
and "
are usable.
-p
, --print "script"
#
Identical to -e
but prints the result.
-c
, --check
#
Syntax check the script without executing.
-i
, --interactive
#
Opens the REPL even if stdin does not appear to be a terminal.
-r
, --require module
#
Preload the specified module at startup.
Follows require()
's module resolution
rules. module
may be either a path to a file, or a node module name.
--no-deprecation
#
Silence deprecation warnings.
--trace-deprecation
#
Print stack traces for deprecations.
--throw-deprecation
#
Throw errors for deprecations.
--no-warnings
#
Silence all process warnings (including deprecations).
--trace-warnings
#
Print stack traces for process warnings (including deprecations).
--redirect-warnings=file
#
Write process warnings to the given file instead of printing to stderr. The file will be created if it does not exist, and will be appended to if it does. If an error occurs while attempting to write the warning to the file, the warning will be written to stderr instead.
--trace-sync-io
#
Prints a stack trace whenever synchronous I/O is detected after the first turn of the event loop.
--zero-fill-buffers
#
Automatically zero-fills all newly allocated Buffer and SlowBuffer instances.
--preserve-symlinks
#
Instructs the module loader to preserve symbolic links when resolving and caching modules.
By default, when Node.js loads a module from a path that is symbolically linked
to a different on-disk location, Node.js will dereference the link and use the
actual on-disk "real path" of the module as both an identifier and as a root
path to locate other dependency modules. In most cases, this default behavior
is acceptable. However, when using symbolically linked peer dependencies, as
illustrated in the example below, the default behavior causes an exception to
be thrown if moduleA
attempts to require moduleB
as a peer dependency:
{appDir}
├── app
│ ├── index.js
│ └── node_modules
│ ├── moduleA -> {appDir}/moduleA
│ └── moduleB
│ ├── index.js
│ └── package.json
└── moduleA
├── index.js
└── package.json
The --preserve-symlinks
command line flag instructs Node.js to use the
symlink path for modules as opposed to the real path, allowing symbolically
linked peer dependencies to be found.
Note, however, that using --preserve-symlinks
can have other side effects.
Specifically, symbolically linked native modules can fail to load if those
are linked from more than one location in the dependency tree (Node.js would
see those as two separate modules and would attempt to load the module multiple
times, causing an exception to be thrown).
--track-heap-objects
#
Track heap object allocations for heap snapshots.
--prof-process
#
Process v8 profiler output generated using the v8 option --prof
.
--v8-options
#
Print v8 command line options.
Note: v8 options allow words to be separated by both dashes (-
) or underscores
(_
).
For example, --stack-trace-limit
is equivalent to --stack_trace_limit
.
--tls-cipher-list=list
#
Specify an alternative default TLS cipher list. (Requires Node.js to be built with crypto support. (Default))
--enable-fips
#
Enable FIPS-compliant crypto at startup. (Requires Node.js to be built with
./configure --openssl-fips
)
--force-fips
#
Force FIPS-compliant crypto on startup. (Cannot be disabled from script code.)
(Same requirements as --enable-fips
)
--openssl-config=file
#
Load an OpenSSL configuration file on startup. Among other uses, this can be
used to enable FIPS-compliant crypto if Node.js is built with
./configure --openssl-fips
.
--use-openssl-ca
, --use-bundled-ca
#
Use OpenSSL's default CA store or use bundled Mozilla CA store as supplied by current Node.js version. The default store is selectable at build-time.
Using OpenSSL store allows for external modifications of the store. For most Linux and BSD distributions, this store is maintained by the distribution maintainers and system administrators. OpenSSL CA store location is dependent on configuration of the OpenSSL library but this can be altered at runtime using environment variables.
The bundled CA store, as supplied by Node.js, is a snapshot of Mozilla CA store that is fixed at release time. It is identical on all supported platforms.
See SSL_CERT_DIR
and SSL_CERT_FILE
.
--icu-data-dir=file
#
Specify ICU data load path. (overrides NODE_ICU_DATA
)
--
#
Indicate the end of node options. Pass the rest of the arguments to the script. If no script filename or eval/print script is supplied prior to this, then the next argument will be used as a script filename.
Environment Variables#
NODE_DEBUG=module[,…]
#
','
-separated list of core modules that should print debug information.
NODE_PATH=path[:…]
#
':'
-separated list of directories prefixed to the module search path.
Note: on Windows, this is a ';'
-separated list instead.
NODE_DISABLE_COLORS=1
#
When set to 1
colors will not be used in the REPL.
NODE_ICU_DATA=file
#
Data path for ICU (Intl object) data. Will extend linked-in data when compiled with small-icu support.
NODE_NO_WARNINGS=1
#
When set to 1
, process warnings are silenced.
NODE_OPTIONS=options...
#
options...
are interpreted as if they had been specified on the command line
before the actual command line (so they can be overriden). Node will exit with
an error if an option that is not allowed in the environment is used, such as
-p
or a script file.
Node options that are allowed are:
--enable-fips
--force-fips
--icu-data-dir
--debug-brk
--debug-port
--debug
--napi-modules
--no-deprecation
--no-warnings
--openssl-config
--redirect-warnings
--require
,-r
--throw-deprecation
--tls-cipher-list
--trace-deprecation
--trace-sync-io
--trace-warnings
--track-heap-objects
--use-bundled-ca
--use-openssl-ca
--v8-pool-size
--zero-fill-buffers
V8 options that are allowed are:
--abort-on-uncaught-exception
--max-old-space-size
NODE_REPL_HISTORY=file
#
Path to the file used to store the persistent REPL history. The default path is
~/.node_repl_history
, which is overridden by this variable. Setting the value
to an empty string (""
or " "
) disables persistent REPL history.
NODE_TTY_UNSAFE_ASYNC=1
#
When set to 1
, writes to stdout
and stderr
will be non-blocking and
asynchronous when outputting to a TTY on platforms which support async stdio.
Setting this will void any guarantee that stdio will not be interleaved or
dropped at program exit. Use of this mode is not recommended.
NODE_EXTRA_CA_CERTS=file
#
When set, the well known "root" CAs (like VeriSign) will be extended with the
extra certificates in file
. The file should consist of one or more trusted
certificates in PEM format. A message will be emitted (once) with
process.emitWarning()
if the file is missing or
malformed, but any errors are otherwise ignored.
Note that neither the well known nor extra certificates are used when the ca
options property is explicitly specified for a TLS or HTTPS client or server.
OPENSSL_CONF=file
#
Load an OpenSSL configuration file on startup. Among other uses, this can be
used to enable FIPS-compliant crypto if Node.js is built with ./configure
--openssl-fips
.
If the --openssl-config
command line option is used, the environment
variable is ignored.
SSL_CERT_DIR=dir
#
If --use-openssl-ca
is enabled, this overrides and sets OpenSSL's directory
containing trusted certificates.
Note: Be aware that unless the child environment is explicitly set, this evironment variable will be inherited by any child processes, and if they use OpenSSL, it may cause them to trust the same CAs as node.
SSL_CERT_FILE=file
#
If --use-openssl-ca
is enabled, this overrides and sets OpenSSL's file
containing trusted certificates.
Note: Be aware that unless the child environment is explicitly set, this evironment variable will be inherited by any child processes, and if they use OpenSSL, it may cause them to trust the same CAs as node.
NODE_REDIRECT_WARNINGS=file
#
When set, process warnings will be emitted to the given file instead of
printing to stderr. The file will be created if it does not exist, and will be
appended to if it does. If an error occurs while attempting to write the
warning to the file, the warning will be written to stderr instead. This is
equivalent to using the --redirect-warnings=file
command-line flag.
Console#
The console
module provides a simple debugging console that is similar to the
JavaScript console mechanism provided by web browsers.
The module exports two specific components:
- A
Console
class with methods such asconsole.log()
,console.error()
andconsole.warn()
that can be used to write to any Node.js stream. - A global
console
instance configured to write toprocess.stdout
andprocess.stderr
. The globalconsole
can be used without callingrequire('console')
.
Warning: The global console object's methods are neither consistently synchronous like the browser APIs they resemble, nor are they consistently asynchronous like all other Node.js streams. See the note on process I/O for more information.
Example using the global console
:
console.log('hello world');
// Prints: hello world, to stdout
console.log('hello %s', 'world');
// Prints: hello world, to stdout
console.error(new Error('Whoops, something bad happened'));
// Prints: [Error: Whoops, something bad happened], to stderr
const name = 'Will Robinson';
console.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to stderr
Example using the Console
class:
const out = getStreamSomehow();
const err = getStreamSomehow();
const myConsole = new console.Console(out, err);
myConsole.log('hello world');
// Prints: hello world, to out
myConsole.log('hello %s', 'world');
// Prints: hello world, to out
myConsole.error(new Error('Whoops, something bad happened'));
// Prints: [Error: Whoops, something bad happened], to err
const name = 'Will Robinson';
myConsole.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to err
Class: Console#
The Console
class can be used to create a simple logger with configurable
output streams and can be accessed using either require('console').Console
or console.Console
:
const Console = require('console').Console;
const Console = console.Console;
new Console(stdout[, stderr])#
Creates a new Console
with one or two writable stream instances. stdout
is a
writable stream to print log or info output. stderr
is used for warning or
error output. If stderr
is not provided, stdout
is used for stderr
.
const output = fs.createWriteStream('./stdout.log');
const errorOutput = fs.createWriteStream('./stderr.log');
// custom simple logger
const logger = new Console(output, errorOutput);
// use it like console
const count = 5;
logger.log('count: %d', count);
// in stdout.log: count 5
The global console
is a special Console
whose output is sent to
process.stdout
and process.stderr
. It is equivalent to calling:
new Console(process.stdout, process.stderr);
console.assert(value[, message][, ...args])#
A simple assertion test that verifies whether value
is truthy. If it is not,
an AssertionError
is thrown. If provided, the error message
is formatted
using util.format()
and used as the error message.
console.assert(true, 'does nothing');
// OK
console.assert(false, 'Whoops %s', 'didn\'t work');
// AssertionError: Whoops didn't work
Note: the console.assert()
method is implemented differently in Node.js
than the console.assert()
method available in browsers.
Specifically, in browsers, calling console.assert()
with a falsy
assertion will cause the message
to be printed to the console without
interrupting execution of subsequent code. In Node.js, however, a falsy
assertion will cause an AssertionError
to be thrown.
Functionality approximating that implemented by browsers can be implemented
by extending Node.js' console
and overriding the console.assert()
method.
In the following example, a simple module is created that extends and overrides
the default behavior of console
in Node.js.
'use strict';
// Creates a simple extension of console with a
// new impl for assert without monkey-patching.
const myConsole = Object.create(console, {
assert: {
value(assertion, message, ...args) {
try {
console.assert(assertion, message, ...args);
} catch (err) {
console.error(err.stack);
}
},
configurable: true,
enumerable: true,
writable: true,
},
});
module.exports = myConsole;
This can then be used as a direct replacement for the built in console:
const console = require('./myConsole');
console.assert(false, 'this message will print, but no error thrown');
console.log('this will also print');
console.clear()#
When stdout
is a TTY, calling console.clear()
will attempt to clear the
TTY. When stdout
is not a TTY, this method does nothing.
Note: The specific operation of console.clear()
can vary across operating
systems and terminal types. For most Linux operating systems, console.clear()
operates similarly to the clear
shell command. On Windows, console.clear()
will clear only the output in the current terminal viewport for the Node.js
binary.
console.count([label])#
label
<string> The display label for the counter. Defaults to'default'
.
Maintains an internal counter specific to label
and outputs to stdout
the
number of times console.count()
has been called with the given label
.
> console.count()
default: 1
undefined
> console.count('default')
default: 2
undefined
> console.count('abc')
abc: 1
undefined
> console.count('xyz')
xyz: 1
undefined
> console.count('abc')
abc: 2
undefined
> console.count()
default: 3
undefined
>
console.countReset([label = 'default'])#
label
<string> The display label for the counter. Defaults to'default'
.
Resets the internal counter specific to label
.
> console.count('abc');
abc: 1
undefined
> console.countReset('abc');
undefined
> console.count('abc');
abc: 1
undefined
>
console.dir(obj[, options])#
Uses util.inspect()
on obj
and prints the resulting string to stdout
.
This function bypasses any custom inspect()
function defined on obj
. An
optional options
object may be passed to alter certain aspects of the
formatted string:
showHidden
- iftrue
then the object's non-enumerable and symbol properties will be shown too. Defaults tofalse
.depth
- tellsutil.inspect()
how many times to recurse while formatting the object. This is useful for inspecting large complicated objects. Defaults to2
. To make it recurse indefinitely, passnull
.colors
- iftrue
, then the output will be styled with ANSI color codes. Defaults tofalse
. Colors are customizable; see customizingutil.inspect()
colors.
console.error([data][, ...args])#
Prints to stderr
with newline. Multiple arguments can be passed, with the
first used as the primary message and all additional used as substitution
values similar to printf(3) (the arguments are all passed to
util.format()
).
const code = 5;
console.error('error #%d', code);
// Prints: error #5, to stderr
console.error('error', code);
// Prints: error 5, to stderr
If formatting elements (e.g. %d
) are not found in the first string then
util.inspect()
is called on each argument and the resulting string
values are concatenated. See util.format()
for more information.
console.info([data][, ...args])#
The console.info()
function is an alias for console.log()
.
console.log([data][, ...args])#
Prints to stdout
with newline. Multiple arguments can be passed, with the
first used as the primary message and all additional used as substitution
values similar to printf(3) (the arguments are all passed to
util.format()
).
const count = 5;
console.log('count: %d', count);
// Prints: count: 5, to stdout
console.log('count:', count);
// Prints: count: 5, to stdout
See util.format()
for more information.
console.time(label)#
label
<string>
Starts a timer that can be used to compute the duration of an operation. Timers
are identified by a unique label
. Use the same label
when you call
console.timeEnd()
to stop the timer and output the elapsed time in
milliseconds to stdout
. Timer durations are accurate to the sub-millisecond.
console.timeEnd(label)#
label
<string>
Stops a timer that was previously started by calling console.time()
and
prints the result to stdout
:
console.time('100-elements');
for (let i = 0; i < 100; i++) ;
console.timeEnd('100-elements');
// prints 100-elements: 225.438ms
Note: As of Node.js v6.0.0, console.timeEnd()
deletes the timer to avoid
leaking it. On older versions, the timer persisted. This allowed
console.timeEnd()
to be called multiple times for the same label. This
functionality was unintended and is no longer supported.
console.trace(message[, ...args])#
Prints to stderr
the string 'Trace :'
, followed by the util.format()
formatted message and stack trace to the current position in the code.
console.trace('Show me');
// Prints: (stack trace will vary based on where trace is called)
// Trace: Show me
// at repl:2:9
// at REPLServer.defaultEval (repl.js:248:27)
// at bound (domain.js:287:14)
// at REPLServer.runBound [as eval] (domain.js:300:12)
// at REPLServer.<anonymous> (repl.js:412:12)
// at emitOne (events.js:82:20)
// at REPLServer.emit (events.js:169:7)
// at REPLServer.Interface._onLine (readline.js:210:10)
// at REPLServer.Interface._line (readline.js:549:8)
// at REPLServer.Interface._ttyWrite (readline.js:826:14)
console.warn([data][, ...args])#
The console.warn()
function is an alias for console.error()
.
Crypto#
The crypto
module provides cryptographic functionality that includes a set of
wrappers for OpenSSL's hash, HMAC, cipher, decipher, sign and verify functions.
Use require('crypto')
to access this module.
const crypto = require('crypto');
const secret = 'abcdefg';
const hash = crypto.createHmac('sha256', secret)
.update('I love cupcakes')
.digest('hex');
console.log(hash);
// Prints:
// c0fa1bc00531bd78ef38c628449c5102aeabd49b5dc3a2a516ea6ea959d6658e
Determining if crypto support is unavailable#
It is possible for Node.js to be built without including support for the
crypto
module. In such cases, calling require('crypto')
will result in an
error being thrown.
let crypto;
try {
crypto = require('crypto');
} catch (err) {
console.log('crypto support is disabled!');
}
Class: Certificate#
SPKAC is a Certificate Signing Request mechanism originally implemented by
Netscape and now specified formally as part of HTML5's keygen
element.
The crypto
module provides the Certificate
class for working with SPKAC
data. The most common usage is handling output generated by the HTML5
<keygen>
element. Node.js uses OpenSSL's SPKAC implementation internally.
new crypto.Certificate()#
Instances of the Certificate
class can be created using the new
keyword
or by calling crypto.Certificate()
as a function:
const crypto = require('crypto');
const cert1 = new crypto.Certificate();
const cert2 = crypto.Certificate();
certificate.exportChallenge(spkac)#
The spkac
data structure includes a public key and a challenge. The
certificate.exportChallenge()
returns the challenge component in the
form of a Node.js Buffer
. The spkac
argument can be either a string
or a Buffer
.
const cert = require('crypto').Certificate();
const spkac = getSpkacSomehow();
const challenge = cert.exportChallenge(spkac);
console.log(challenge.toString('utf8'));
// Prints: the challenge as a UTF8 string
certificate.exportPublicKey(spkac)#
The spkac
data structure includes a public key and a challenge. The
certificate.exportPublicKey()
returns the public key component in the
form of a Node.js Buffer
. The spkac
argument can be either a string
or a Buffer
.
const cert = require('crypto').Certificate();
const spkac = getSpkacSomehow();
const publicKey = cert.exportPublicKey(spkac);
console.log(publicKey);
// Prints: the public key as <Buffer ...>
certificate.verifySpkac(spkac)#
Returns true
if the given spkac
data structure is valid, false
otherwise.
The spkac
argument must be a Node.js Buffer
.
const cert = require('crypto').Certificate();
const spkac = getSpkacSomehow();
console.log(cert.verifySpkac(Buffer.from(spkac)));
// Prints: true or false
Class: Cipher#
Instances of the Cipher
class are used to encrypt data. The class can be
used in one of two ways:
- As a stream that is both readable and writable, where plain unencrypted data is written to produce encrypted data on the readable side, or
- Using the
cipher.update()
andcipher.final()
methods to produce the encrypted data.
The crypto.createCipher()
or crypto.createCipheriv()
methods are
used to create Cipher
instances. Cipher
objects are not to be created
directly using the new
keyword.
Example: Using Cipher
objects as streams:
const crypto = require('crypto');
const cipher = crypto.createCipher('aes192', 'a password');
let encrypted = '';
cipher.on('readable', () => {
const data = cipher.read();
if (data)
encrypted += data.toString('hex');
});
cipher.on('end', () => {
console.log(encrypted);
// Prints: ca981be48e90867604588e75d04feabb63cc007a8f8ad89b10616ed84d815504
});
cipher.write('some clear text data');
cipher.end();
Example: Using Cipher
and piped streams:
const crypto = require('crypto');
const fs = require('fs');
const cipher = crypto.createCipher('aes192', 'a password');
const input = fs.createReadStream('test.js');
const output = fs.createWriteStream('test.enc');
input.pipe(cipher).pipe(output);
Example: Using the cipher.update()
and cipher.final()
methods:
const crypto = require('crypto');
const cipher = crypto.createCipher('aes192', 'a password');
let encrypted = cipher.update('some clear text data', 'utf8', 'hex');
encrypted += cipher.final('hex');
console.log(encrypted);
// Prints: ca981be48e90867604588e75d04feabb63cc007a8f8ad89b10616ed84d815504
cipher.final([output_encoding])#
Returns any remaining enciphered contents. If output_encoding
parameter is one of 'latin1'
, 'base64'
or 'hex'
, a string is returned.
If an output_encoding
is not provided, a Buffer
is returned.
Once the cipher.final()
method has been called, the Cipher
object can no
longer be used to encrypt data. Attempts to call cipher.final()
more than
once will result in an error being thrown.
cipher.setAAD(buffer)#
When using an authenticated encryption mode (only GCM
is currently
supported), the cipher.setAAD()
method sets the value used for the
additional authenticated data (AAD) input parameter.
Returns this
for method chaining.
cipher.getAuthTag()#
When using an authenticated encryption mode (only GCM
is currently
supported), the cipher.getAuthTag()
method returns a Buffer
containing
the authentication tag that has been computed from the given data.
The cipher.getAuthTag()
method should only be called after encryption has
been completed using the cipher.final()
method.
cipher.setAutoPadding(auto_padding=true)#
When using block encryption algorithms, the Cipher
class will automatically
add padding to the input data to the appropriate block size. To disable the
default padding call cipher.setAutoPadding(false)
.
When auto_padding
is false
, the length of the entire input data must be a
multiple of the cipher's block size or cipher.final()
will throw an Error.
Disabling automatic padding is useful for non-standard padding, for instance
using 0x0
instead of PKCS padding.
The cipher.setAutoPadding()
method must be called before cipher.final()
.
Returns this
for method chaining.
cipher.update(data[, input_encoding][, output_encoding])#
Updates the cipher with data
. If the input_encoding
argument is given,
its value must be one of 'utf8'
, 'ascii'
, or 'latin1'
and the data
argument is a string using the specified encoding. If the input_encoding
argument is not given, data
must be a Buffer
. If data
is a
Buffer
then input_encoding
is ignored.
The output_encoding
specifies the output format of the enciphered
data, and can be 'latin1'
, 'base64'
or 'hex'
. If the output_encoding
is specified, a string using the specified encoding is returned. If no
output_encoding
is provided, a Buffer
is returned.
The cipher.update()
method can be called multiple times with new data until
cipher.final()
is called. Calling cipher.update()
after
cipher.final()
will result in an error being thrown.
Class: Decipher#
Instances of the Decipher
class are used to decrypt data. The class can be
used in one of two ways:
- As a stream that is both readable and writable, where plain encrypted data is written to produce unencrypted data on the readable side, or
- Using the
decipher.update()
anddecipher.final()
methods to produce the unencrypted data.
The crypto.createDecipher()
or crypto.createDecipheriv()
methods are
used to create Decipher
instances. Decipher
objects are not to be created
directly using the new
keyword.
Example: Using Decipher
objects as streams:
const crypto = require('crypto');
const decipher = crypto.createDecipher('aes192', 'a password');
let decrypted = '';
decipher.on('readable', () => {
const data = decipher.read();
if (data)
decrypted += data.toString('utf8');
});
decipher.on('end', () => {
console.log(decrypted);
// Prints: some clear text data
});
const encrypted =
'ca981be48e90867604588e75d04feabb63cc007a8f8ad89b10616ed84d815504';
decipher.write(encrypted, 'hex');
decipher.end();
Example: Using Decipher
and piped streams:
const crypto = require('crypto');
const fs = require('fs');
const decipher = crypto.createDecipher('aes192', 'a password');
const input = fs.createReadStream('test.enc');
const output = fs.createWriteStream('test.js');
input.pipe(decipher).pipe(output);
Example: Using the decipher.update()
and decipher.final()
methods:
const crypto = require('crypto');
const decipher = crypto.createDecipher('aes192', 'a password');
const encrypted =
'ca981be48e90867604588e75d04feabb63cc007a8f8ad89b10616ed84d815504';
let decrypted = decipher.update(encrypted, 'hex', 'utf8');
decrypted += decipher.final('utf8');
console.log(decrypted);
// Prints: some clear text data
decipher.final([output_encoding])#
Returns any remaining deciphered contents. If output_encoding
parameter is one of 'latin1'
, 'ascii'
or 'utf8'
, a string is returned.
If an output_encoding
is not provided, a Buffer
is returned.
Once the decipher.final()
method has been called, the Decipher
object can
no longer be used to decrypt data. Attempts to call decipher.final()
more
than once will result in an error being thrown.
decipher.setAAD(buffer)#
When using an authenticated encryption mode (only GCM
is currently
supported), the decipher.setAAD()
method sets the value used for the
additional authenticated data (AAD) input parameter.
Returns this
for method chaining.
decipher.setAuthTag(buffer)#
When using an authenticated encryption mode (only GCM
is currently
supported), the decipher.setAuthTag()
method is used to pass in the
received authentication tag. If no tag is provided, or if the cipher text
has been tampered with, decipher.final()
will throw, indicating that the
cipher text should be discarded due to failed authentication.
Returns this
for method chaining.
decipher.setAutoPadding(auto_padding=true)#
When data has been encrypted without standard block padding, calling
decipher.setAutoPadding(false)
will disable automatic padding to prevent
decipher.final()
from checking for and removing padding.
Turning auto padding off will only work if the input data's length is a multiple of the ciphers block size.
The decipher.setAutoPadding()
method must be called before
decipher.update()
.
Returns this
for method chaining.
decipher.update(data[, input_encoding][, output_encoding])#
Updates the decipher with data
. If the input_encoding
argument is given,
its value must be one of 'latin1'
, 'base64'
, or 'hex'
and the data
argument is a string using the specified encoding. If the input_encoding
argument is not given, data
must be a Buffer
. If data
is a
Buffer
then input_encoding
is ignored.
The output_encoding
specifies the output format of the enciphered
data, and can be 'latin1'
, 'ascii'
or 'utf8'
. If the output_encoding
is specified, a string using the specified encoding is returned. If no
output_encoding
is provided, a Buffer
is returned.
The decipher.update()
method can be called multiple times with new data until
decipher.final()
is called. Calling decipher.update()
after
decipher.final()
will result in an error being thrown.
Class: DiffieHellman#
The DiffieHellman
class is a utility for creating Diffie-Hellman key
exchanges.
Instances of the DiffieHellman
class can be created using the
crypto.createDiffieHellman()
function.
const crypto = require('crypto');
const assert = require('assert');
// Generate Alice's keys...
const alice = crypto.createDiffieHellman(2048);
const aliceKey = alice.generateKeys();
// Generate Bob's keys...
const bob = crypto.createDiffieHellman(alice.getPrime(), alice.getGenerator());
const bobKey = bob.generateKeys();
// Exchange and generate the secret...
const aliceSecret = alice.computeSecret(bobKey);
const bobSecret = bob.computeSecret(aliceKey);
// OK
assert.strictEqual(aliceSecret.toString('hex'), bobSecret.toString('hex'));
diffieHellman.computeSecret(other_public_key[, input_encoding][, output_encoding])#
Computes the shared secret using other_public_key
as the other
party's public key and returns the computed shared secret. The supplied
key is interpreted using the specified input_encoding
, and secret is
encoded using specified output_encoding
. Encodings can be
'latin1'
, 'hex'
, or 'base64'
. If the input_encoding
is not
provided, other_public_key
is expected to be a Buffer
.
If output_encoding
is given a string is returned; otherwise, a
Buffer
is returned.
diffieHellman.generateKeys([encoding])#
Generates private and public Diffie-Hellman key values, and returns
the public key in the specified encoding
. This key should be
transferred to the other party. Encoding can be 'latin1'
, 'hex'
,
or 'base64'
. If encoding
is provided a string is returned; otherwise a
Buffer
is returned.
diffieHellman.getGenerator([encoding])#
Returns the Diffie-Hellman generator in the specified encoding
, which can
be 'latin1'
, 'hex'
, or 'base64'
. If encoding
is provided a string is
returned; otherwise a Buffer
is returned.
diffieHellman.getPrime([encoding])#
Returns the Diffie-Hellman prime in the specified encoding
, which can
be 'latin1'
, 'hex'
, or 'base64'
. If encoding
is provided a string is
returned; otherwise a Buffer
is returned.
diffieHellman.getPrivateKey([encoding])#
Returns the Diffie-Hellman private key in the specified encoding
,
which can be 'latin1'
, 'hex'
, or 'base64'
. If encoding
is provided a
string is returned; otherwise a Buffer
is returned.
diffieHellman.getPublicKey([encoding])#
Returns the Diffie-Hellman public key in the specified encoding
, which
can be 'latin1'
, 'hex'
, or 'base64'
. If encoding
is provided a
string is returned; otherwise a Buffer
is returned.
diffieHellman.setPrivateKey(private_key[, encoding])#
Sets the Diffie-Hellman private key. If the encoding
argument is provided
and is either 'latin1'
, 'hex'
, or 'base64'
, private_key
is expected
to be a string. If no encoding
is provided, private_key
is expected
to be a Buffer
.
diffieHellman.setPublicKey(public_key[, encoding])#
Sets the Diffie-Hellman public key. If the encoding
argument is provided
and is either 'latin1'
, 'hex'
or 'base64'
, public_key
is expected
to be a string. If no encoding
is provided, public_key
is expected
to be a Buffer
.
diffieHellman.verifyError#
A bit field containing any warnings and/or errors resulting from a check
performed during initialization of the DiffieHellman
object.
The following values are valid for this property (as defined in constants
module):
DH_CHECK_P_NOT_SAFE_PRIME
DH_CHECK_P_NOT_PRIME
DH_UNABLE_TO_CHECK_GENERATOR
DH_NOT_SUITABLE_GENERATOR
Class: ECDH#
The ECDH
class is a utility for creating Elliptic Curve Diffie-Hellman (ECDH)
key exchanges.
Instances of the ECDH
class can be created using the
crypto.createECDH()
function.
const crypto = require('crypto');
const assert = require('assert');
// Generate Alice's keys...
const alice = crypto.createECDH('secp521r1');
const aliceKey = alice.generateKeys();
// Generate Bob's keys...
const bob = crypto.createECDH('secp521r1');
const bobKey = bob.generateKeys();
// Exchange and generate the secret...
const aliceSecret = alice.computeSecret(bobKey);
const bobSecret = bob.computeSecret(aliceKey);
assert.strictEqual(aliceSecret.toString('hex'), bobSecret.toString('hex'));
// OK
ecdh.computeSecret(other_public_key[, input_encoding][, output_encoding])#
Computes the shared secret using other_public_key
as the other
party's public key and returns the computed shared secret. The supplied
key is interpreted using specified input_encoding
, and the returned secret
is encoded using the specified output_encoding
. Encodings can be
'latin1'
, 'hex'
, or 'base64'
. If the input_encoding
is not
provided, other_public_key
is expected to be a Buffer
.
If output_encoding
is given a string will be returned; otherwise a
Buffer
is returned.
ecdh.generateKeys([encoding[, format]])#
Generates private and public EC Diffie-Hellman key values, and returns
the public key in the specified format
and encoding
. This key should be
transferred to the other party.
The format
arguments specifies point encoding and can be 'compressed'
,
'uncompressed'
, or 'hybrid'
. If format
is not specified, the point will
be returned in 'uncompressed'
format.
The encoding
argument can be 'latin1'
, 'hex'
, or 'base64'
. If
encoding
is provided a string is returned; otherwise a Buffer
is returned.
ecdh.getPrivateKey([encoding])#
Returns the EC Diffie-Hellman private key in the specified encoding
,
which can be 'latin1'
, 'hex'
, or 'base64'
. If encoding
is provided
a string is returned; otherwise a Buffer
is returned.
ecdh.getPublicKey([encoding[, format]])#
Returns the EC Diffie-Hellman public key in the specified encoding
and
format
.
The format
argument specifies point encoding and can be 'compressed'
,
'uncompressed'
, or 'hybrid'
. If format
is not specified the point will be
returned in 'uncompressed'
format.
The encoding
argument can be 'latin1'
, 'hex'
, or 'base64'
. If
encoding
is specified, a string is returned; otherwise a Buffer
is
returned.
ecdh.setPrivateKey(private_key[, encoding])#
Sets the EC Diffie-Hellman private key. The encoding
can be 'latin1'
,
'hex'
or 'base64'
. If encoding
is provided, private_key
is expected
to be a string; otherwise private_key
is expected to be a Buffer
. If
private_key
is not valid for the curve specified when the ECDH
object was
created, an error is thrown. Upon setting the private key, the associated
public point (key) is also generated and set in the ECDH object.
ecdh.setPublicKey(public_key[, encoding])#
Sets the EC Diffie-Hellman public key. Key encoding can be 'latin1'
,
'hex'
or 'base64'
. If encoding
is provided public_key
is expected to
be a string; otherwise a Buffer
is expected.
Note that there is not normally a reason to call this method because ECDH
only requires a private key and the other party's public key to compute the
shared secret. Typically either ecdh.generateKeys()
or
ecdh.setPrivateKey()
will be called. The ecdh.setPrivateKey()
method
attempts to generate the public point/key associated with the private key being
set.
Example (obtaining a shared secret):
const crypto = require('crypto');
const alice = crypto.createECDH('secp256k1');
const bob = crypto.createECDH('secp256k1');
// Note: This is a shortcut way to specify one of Alice's previous private
// keys. It would be unwise to use such a predictable private key in a real
// application.
alice.setPrivateKey(
crypto.createHash('sha256').update('alice', 'utf8').digest()
);
// Bob uses a newly generated cryptographically strong
// pseudorandom key pair
bob.generateKeys();
const aliceSecret = alice.computeSecret(bob.getPublicKey(), null, 'hex');
const bobSecret = bob.computeSecret(alice.getPublicKey(), null, 'hex');
// aliceSecret and bobSecret should be the same shared secret value
console.log(aliceSecret === bobSecret);
Class: Hash#
The Hash
class is a utility for creating hash digests of data. It can be
used in one of two ways:
- As a stream that is both readable and writable, where data is written to produce a computed hash digest on the readable side, or
- Using the
hash.update()
andhash.digest()
methods to produce the computed hash.
The crypto.createHash()
method is used to create Hash
instances. Hash
objects are not to be created directly using the new
keyword.
Example: Using Hash
objects as streams:
const crypto = require('crypto');
const hash = crypto.createHash('sha256');
hash.on('readable', () => {
const data = hash.read();
if (data) {
console.log(data.toString('hex'));
// Prints:
// 6a2da20943931e9834fc12cfe5bb47bbd9ae43489a30726962b576f4e3993e50
}
});
hash.write('some data to hash');
hash.end();
Example: Using Hash
and piped streams:
const crypto = require('crypto');
const fs = require('fs');
const hash = crypto.createHash('sha256');
const input = fs.createReadStream('test.js');
input.pipe(hash).pipe(process.stdout);
Example: Using the hash.update()
and hash.digest()
methods:
const crypto = require('crypto');
const hash = crypto.createHash('sha256');
hash.update('some data to hash');
console.log(hash.digest('hex'));
// Prints:
// 6a2da20943931e9834fc12cfe5bb47bbd9ae43489a30726962b576f4e3993e50
hash.digest([encoding])#
Calculates the digest of all of the data passed to be hashed (using the
hash.update()
method). The encoding
can be 'hex'
, 'latin1'
or
'base64'
. If encoding
is provided a string will be returned; otherwise
a Buffer
is returned.
The Hash
object can not be used again after hash.digest()
method has been
called. Multiple calls will cause an error to be thrown.
hash.update(data[, input_encoding])#
Updates the hash content with the given data
, the encoding of which
is given in input_encoding
and can be 'utf8'
, 'ascii'
or
'latin1'
. If encoding
is not provided, and the data
is a string, an
encoding of 'utf8'
is enforced. If data
is a Buffer
then
input_encoding
is ignored.
This can be called many times with new data as it is streamed.
Class: Hmac#
The Hmac
Class is a utility for creating cryptographic HMAC digests. It can
be used in one of two ways:
- As a stream that is both readable and writable, where data is written to produce a computed HMAC digest on the readable side, or
- Using the
hmac.update()
andhmac.digest()
methods to produce the computed HMAC digest.
The crypto.createHmac()
method is used to create Hmac
instances. Hmac
objects are not to be created directly using the new
keyword.
Example: Using Hmac
objects as streams:
const crypto = require('crypto');
const hmac = crypto.createHmac('sha256', 'a secret');
hmac.on('readable', () => {
const data = hmac.read();
if (data) {
console.log(data.toString('hex'));
// Prints:
// 7fd04df92f636fd450bc841c9418e5825c17f33ad9c87c518115a45971f7f77e
}
});
hmac.write('some data to hash');
hmac.end();
Example: Using Hmac
and piped streams:
const crypto = require('crypto');
const fs = require('fs');
const hmac = crypto.createHmac('sha256', 'a secret');
const input = fs.createReadStream('test.js');
input.pipe(hmac).pipe(process.stdout);
Example: Using the hmac.update()
and hmac.digest()
methods:
const crypto = require('crypto');
const hmac = crypto.createHmac('sha256', 'a secret');
hmac.update('some data to hash');
console.log(hmac.digest('hex'));
// Prints:
// 7fd04df92f636fd450bc841c9418e5825c17f33ad9c87c518115a45971f7f77e
hmac.digest([encoding])#
Calculates the HMAC digest of all of the data passed using hmac.update()
.
The encoding
can be 'hex'
, 'latin1'
or 'base64'
. If encoding
is
provided a string is returned; otherwise a Buffer
is returned;
The Hmac
object can not be used again after hmac.digest()
has been
called. Multiple calls to hmac.digest()
will result in an error being thrown.
hmac.update(data[, input_encoding])#
Updates the Hmac
content with the given data
, the encoding of which
is given in input_encoding
and can be 'utf8'
, 'ascii'
or
'latin1'
. If encoding
is not provided, and the data
is a string, an
encoding of 'utf8'
is enforced. If data
is a Buffer
then
input_encoding
is ignored.
This can be called many times with new data as it is streamed.
Class: Sign#
The Sign
Class is a utility for generating signatures. It can be used in one
of two ways:
- As a writable stream, where data to be signed is written and the
sign.sign()
method is used to generate and return the signature, or - Using the
sign.update()
andsign.sign()
methods to produce the signature.
The crypto.createSign()
method is used to create Sign
instances. The
argument is the string name of the hash function to use. Sign
objects are not
to be created directly using the new
keyword.
Example: Using Sign
objects as streams:
const crypto = require('crypto');
const sign = crypto.createSign('SHA256');
sign.write('some data to sign');
sign.end();
const privateKey = getPrivateKeySomehow();
console.log(sign.sign(privateKey, 'hex'));
// Prints: the calculated signature using the specified private key and
// SHA-256. For RSA keys, the algorithm is RSASSA-PKCS1-v1_5 (see padding
// parameter below for RSASSA-PSS). For EC keys, the algorithm is ECDSA.
Example: Using the sign.update()
and sign.sign()
methods:
const crypto = require('crypto');
const sign = crypto.createSign('SHA256');
sign.update('some data to sign');
const privateKey = getPrivateKeySomehow();
console.log(sign.sign(privateKey, 'hex'));
// Prints: the calculated signature
In some cases, a Sign
instance can also be created by passing in a signature
algorithm name, such as 'RSA-SHA256'. This will use the corresponding digest
algorithm. This does not work for all signature algorithms, such as
'ecdsa-with-SHA256'. Use digest names instead.
Example: signing using legacy signature algorithm name
const crypto = require('crypto');
const sign = crypto.createSign('RSA-SHA256');
sign.update('some data to sign');
const privateKey = getPrivateKeySomehow();
console.log(sign.sign(privateKey, 'hex'));
// Prints: the calculated signature
sign.sign(private_key[, output_format])#
Calculates the signature on all the data passed through using either
sign.update()
or sign.write()
.
The private_key
argument can be an object or a string. If private_key
is a
string, it is treated as a raw key with no passphrase. If private_key
is an
object, it must contain one or more of the following properties:
key
: <string> - PEM encoded private key (required)passphrase
: <string> - passphrase for the private keypadding
: <integer> - Optional padding value for RSA, one of the following:crypto.constants.RSA_PKCS1_PADDING
(default)crypto.constants.RSA_PKCS1_PSS_PADDING
Note that
RSA_PKCS1_PSS_PADDING
will use MGF1 with the same hash function used to sign the message as specified in section 3.1 of RFC 4055.saltLength
: <integer> - salt length for when padding isRSA_PKCS1_PSS_PADDING
. The special valuecrypto.constants.RSA_PSS_SALTLEN_DIGEST
sets the salt length to the digest size,crypto.constants.RSA_PSS_SALTLEN_MAX_SIGN
(default) sets it to the maximum permissible value.
The output_format
can specify one of 'latin1'
, 'hex'
or 'base64'
. If
output_format
is provided a string is returned; otherwise a Buffer
is
returned.
The Sign
object can not be again used after sign.sign()
method has been
called. Multiple calls to sign.sign()
will result in an error being thrown.
sign.update(data[, input_encoding])#
Updates the Sign
content with the given data
, the encoding of which
is given in input_encoding
and can be 'utf8'
, 'ascii'
or
'latin1'
. If encoding
is not provided, and the data
is a string, an
encoding of 'utf8'
is enforced. If data
is a Buffer
then
input_encoding
is ignored.
This can be called many times with new data as it is streamed.
Class: Verify#
The Verify
class is a utility for verifying signatures. It can be used in one
of two ways:
- As a writable stream where written data is used to validate against the supplied signature, or
- Using the
verify.update()
andverify.verify()
methods to verify the signature.
The crypto.createVerify()
method is used to create Verify
instances.
Verify
objects are not to be created directly using the new
keyword.
Example: Using Verify
objects as streams:
const crypto = require('crypto');
const verify = crypto.createVerify('SHA256');
verify.write('some data to sign');
verify.end();
const publicKey = getPublicKeySomehow();
const signature = getSignatureToVerify();
console.log(verify.verify(publicKey, signature));
// Prints: true or false
Example: Using the verify.update()
and verify.verify()
methods:
const crypto = require('crypto');
const verify = crypto.createVerify('SHA256');
verify.update('some data to sign');
const publicKey = getPublicKeySomehow();
const signature = getSignatureToVerify();
console.log(verify.verify(publicKey, signature));
// Prints: true or false
verifier.update(data[, input_encoding])#
Updates the Verify
content with the given data
, the encoding of which
is given in input_encoding
and can be 'utf8'
, 'ascii'
or
'latin1'
. If encoding
is not provided, and the data
is a string, an
encoding of 'utf8'
is enforced. If data
is a Buffer
then
input_encoding
is ignored.
This can be called many times with new data as it is streamed.
verifier.verify(object, signature[, signature_format])#
Verifies the provided data using the given object
and signature
.
The object
argument can be either a string containing a PEM encoded object,
which can be an RSA public key, a DSA public key, or an X.509 certificate,
or an object with one or more of the following properties:
key
: <string> - PEM encoded public key (required)padding
: <integer> - Optional padding value for RSA, one of the following:crypto.constants.RSA_PKCS1_PADDING
(default)crypto.constants.RSA_PKCS1_PSS_PADDING
Note that
RSA_PKCS1_PSS_PADDING
will use MGF1 with the same hash function used to verify the message as specified in section 3.1 of RFC 4055.saltLength
: <integer> - salt length for when padding isRSA_PKCS1_PSS_PADDING
. The special valuecrypto.constants.RSA_PSS_SALTLEN_DIGEST
sets the salt length to the digest size,crypto.constants.RSA_PSS_SALTLEN_AUTO
(default) causes it to be determined automatically.
The signature
argument is the previously calculated signature for the data, in
the signature_format
which can be 'latin1'
, 'hex'
or 'base64'
.
If a signature_format
is specified, the signature
is expected to be a
string; otherwise signature
is expected to be a Buffer
.
Returns true
or false
depending on the validity of the signature for
the data and public key.
The verifier
object can not be used again after verify.verify()
has been
called. Multiple calls to verify.verify()
will result in an error being
thrown.
crypto
module methods and properties#
crypto.constants#
Returns an object containing commonly used constants for crypto and security related operations. The specific constants currently defined are described in Crypto Constants.
crypto.DEFAULT_ENCODING#
The default encoding to use for functions that can take either strings
or buffers. The default value is 'buffer'
, which makes methods
default to Buffer
objects.
The crypto.DEFAULT_ENCODING
mechanism is provided for backwards compatibility
with legacy programs that expect 'latin1'
to be the default encoding.
New applications should expect the default to be 'buffer'
. This property may
become deprecated in a future Node.js release.
crypto.fips#
Property for checking and controlling whether a FIPS compliant crypto provider is currently in use. Setting to true requires a FIPS build of Node.js.
crypto.createCipher(algorithm, password)#
Creates and returns a Cipher
object that uses the given algorithm
and
password
.
The algorithm
is dependent on OpenSSL, examples are 'aes192'
, etc. On
recent OpenSSL releases, openssl list-cipher-algorithms
will display the
available cipher algorithms.
The password
is used to derive the cipher key and initialization vector (IV).
The value must be either a 'latin1'
encoded string or a Buffer
.
The implementation of crypto.createCipher()
derives keys using the OpenSSL
function EVP_BytesToKey
with the digest algorithm set to MD5, one
iteration, and no salt. The lack of salt allows dictionary attacks as the same
password always creates the same key. The low iteration count and
non-cryptographically secure hash algorithm allow passwords to be tested very
rapidly.
In line with OpenSSL's recommendation to use PBKDF2 instead of
EVP_BytesToKey
it is recommended that developers derive a key and IV on
their own using crypto.pbkdf2()
and to use crypto.createCipheriv()
to create the Cipher
object. Users should not use ciphers with counter mode
(e.g. CTR, GCM or CCM) in crypto.createCipher()
. A warning is emitted when
they are used in order to avoid the risk of IV reuse that causes
vulnerabilities. For the case when IV is reused in GCM, see Nonce-Disrespecting
Adversaries for details.
crypto.createCipheriv(algorithm, key, iv)#
Creates and returns a Cipher
object, with the given algorithm
, key
and
initialization vector (iv
).
The algorithm
is dependent on OpenSSL, examples are 'aes192'
, etc. On
recent OpenSSL releases, openssl list-cipher-algorithms
will display the
available cipher algorithms.
The key
is the raw key used by the algorithm
and iv
is an
initialization vector. Both arguments must be 'utf8'
encoded strings or
buffers.
crypto.createCredentials(details)#
tls.createSecureContext()
instead.details
<Object> Identical totls.createSecureContext()
.
The crypto.createCredentials()
method is a deprecated function for creating
and returning a tls.SecureContext
. It should not be used. Replace it with
tls.createSecureContext()
which has the exact same arguments and return
value.
Returns a tls.SecureContext
, as-if tls.createSecureContext()
had been
called.
crypto.createDecipher(algorithm, password)#
Creates and returns a Decipher
object that uses the given algorithm
and
password
(key).
The implementation of crypto.createDecipher()
derives keys using the OpenSSL
function EVP_BytesToKey
with the digest algorithm set to MD5, one
iteration, and no salt. The lack of salt allows dictionary attacks as the same
password always creates the same key. The low iteration count and
non-cryptographically secure hash algorithm allow passwords to be tested very
rapidly.
In line with OpenSSL's recommendation to use PBKDF2 instead of
EVP_BytesToKey
it is recommended that developers derive a key and IV on
their own using crypto.pbkdf2()
and to use crypto.createDecipheriv()
to create the Decipher
object.
crypto.createDecipheriv(algorithm, key, iv)#
Creates and returns a Decipher
object that uses the given algorithm
, key
and initialization vector (iv
).
The algorithm
is dependent on OpenSSL, examples are 'aes192'
, etc. On
recent OpenSSL releases, openssl list-cipher-algorithms
will display the
available cipher algorithms.
The key
is the raw key used by the algorithm
and iv
is an
initialization vector. Both arguments must be 'utf8'
encoded strings or
buffers.
crypto.createDiffieHellman(prime[, prime_encoding][, generator][, generator_encoding])#
Creates a DiffieHellman
key exchange object using the supplied prime
and an
optional specific generator
.
The generator
argument can be a number, string, or Buffer
. If
generator
is not specified, the value 2
is used.
The prime_encoding
and generator_encoding
arguments can be 'latin1'
,
'hex'
, or 'base64'
.
If prime_encoding
is specified, prime
is expected to be a string; otherwise
a Buffer
is expected.
If generator_encoding
is specified, generator
is expected to be a string;
otherwise either a number or Buffer
is expected.
crypto.createDiffieHellman(prime_length[, generator])#
Creates a DiffieHellman
key exchange object and generates a prime of
prime_length
bits using an optional specific numeric generator
.
If generator
is not specified, the value 2
is used.
crypto.createECDH(curve_name)#
Creates an Elliptic Curve Diffie-Hellman (ECDH
) key exchange object using a
predefined curve specified by the curve_name
string. Use
crypto.getCurves()
to obtain a list of available curve names. On recent
OpenSSL releases, openssl ecparam -list_curves
will also display the name
and description of each available elliptic curve.
crypto.createHash(algorithm)#
Creates and returns a Hash
object that can be used to generate hash digests
using the given algorithm
.
The algorithm
is dependent on the available algorithms supported by the
version of OpenSSL on the platform. Examples are 'sha256'
, 'sha512'
, etc.
On recent releases of OpenSSL, openssl list-message-digest-algorithms
will
display the available digest algorithms.
Example: generating the sha256 sum of a file
const filename = process.argv[2];
const crypto = require('crypto');
const fs = require('fs');
const hash = crypto.createHash('sha256');
const input = fs.createReadStream(filename);
input.on('readable', () => {
const data = input.read();
if (data)
hash.update(data);
else {
console.log(`${hash.digest('hex')} ${filename}`);
}
});
crypto.createHmac(algorithm, key)#
Creates and returns an Hmac
object that uses the given algorithm
and key
.
The algorithm
is dependent on the available algorithms supported by the
version of OpenSSL on the platform. Examples are 'sha256'
, 'sha512'
, etc.
On recent releases of OpenSSL, openssl list-message-digest-algorithms
will
display the available digest algorithms.
The key
is the HMAC key used to generate the cryptographic HMAC hash.
Example: generating the sha256 HMAC of a file
const filename = process.argv[2];
const crypto = require('crypto');
const fs = require('fs');
const hmac = crypto.createHmac('sha256', 'a secret');
const input = fs.createReadStream(filename);
input.on('readable', () => {
const data = input.read();
if (data)
hmac.update(data);
else {
console.log(`${hmac.digest('hex')} ${filename}`);
}
});
crypto.createSign(algorithm)#
Creates and returns a Sign
object that uses the given algorithm
.
Use crypto.getHashes()
to obtain an array of names of the available
signing algorithms.
crypto.createVerify(algorithm)#
Creates and returns a Verify
object that uses the given algorithm.
Use crypto.getHashes()
to obtain an array of names of the available
signing algorithms.
crypto.getCiphers()#
Returns an array with the names of the supported cipher algorithms.
Example:
const ciphers = crypto.getCiphers();
console.log(ciphers); // ['aes-128-cbc', 'aes-128-ccm', ...]
crypto.getCurves()#
Returns an array with the names of the supported elliptic curves.
Example:
const curves = crypto.getCurves();
console.log(curves); // ['Oakley-EC2N-3', 'Oakley-EC2N-4', ...]
crypto.getDiffieHellman(group_name)#
Creates a predefined DiffieHellman
key exchange object. The
supported groups are: 'modp1'
, 'modp2'
, 'modp5'
(defined in
RFC 2412, but see Caveats) and 'modp14'
, 'modp15'
,
'modp16'
, 'modp17'
, 'modp18'
(defined in RFC 3526). The
returned object mimics the interface of objects created by
crypto.createDiffieHellman()
, but will not allow changing
the keys (with diffieHellman.setPublicKey()
for example). The
advantage of using this method is that the parties do not have to
generate nor exchange a group modulus beforehand, saving both processor
and communication time.
Example (obtaining a shared secret):
const crypto = require('crypto');
const alice = crypto.getDiffieHellman('modp14');
const bob = crypto.getDiffieHellman('modp14');
alice.generateKeys();
bob.generateKeys();
const aliceSecret = alice.computeSecret(bob.getPublicKey(), null, 'hex');
const bobSecret = bob.computeSecret(alice.getPublicKey(), null, 'hex');
/* aliceSecret and bobSecret should be the same */
console.log(aliceSecret === bobSecret);
crypto.getHashes()#
Returns an array of the names of the supported hash algorithms,
such as RSA-SHA256
.
Example:
const hashes = crypto.getHashes();
console.log(hashes); // ['DSA', 'DSA-SHA', 'DSA-SHA1', ...]
crypto.pbkdf2(password, salt, iterations, keylen, digest, callback)#
Provides an asynchronous Password-Based Key Derivation Function 2 (PBKDF2)
implementation. A selected HMAC digest algorithm specified by digest
is
applied to derive a key of the requested byte length (keylen
) from the
password
, salt
and iterations
.
The supplied callback
function is called with two arguments: err
and
derivedKey
. If an error occurs, err
will be set; otherwise err
will be
null. The successfully generated derivedKey
will be passed as a Buffer
.
The iterations
argument must be a number set as high as possible. The
higher the number of iterations, the more secure the derived key will be,
but will take a longer amount of time to complete.
The salt
should also be as unique as possible. It is recommended that the
salts are random and their lengths are at least 16 bytes. See
NIST SP 800-132 for details.
Example:
const crypto = require('crypto');
crypto.pbkdf2('secret', 'salt', 100000, 512, 'sha512', (err, key) => {
if (err) throw err;
console.log(key.toString('hex')); // '3745e48...aa39b34'
});
An array of supported digest functions can be retrieved using
crypto.getHashes()
.
crypto.pbkdf2Sync(password, salt, iterations, keylen, digest)#
Provides a synchronous Password-Based Key Derivation Function 2 (PBKDF2)
implementation. A selected HMAC digest algorithm specified by digest
is
applied to derive a key of the requested byte length (keylen
) from the
password
, salt
and iterations
.
If an error occurs an Error will be thrown, otherwise the derived key will be
returned as a Buffer
.
The iterations
argument must be a number set as high as possible. The
higher the number of iterations, the more secure the derived key will be,
but will take a longer amount of time to complete.
The salt
should also be as unique as possible. It is recommended that the
salts are random and their lengths are at least 16 bytes. See
NIST SP 800-132 for details.
Example:
const crypto = require('crypto');
const key = crypto.pbkdf2Sync('secret', 'salt', 100000, 512, 'sha512');
console.log(key.toString('hex')); // '3745e48...aa39b34'
An array of supported digest functions can be retrieved using
crypto.getHashes()
.
crypto.privateDecrypt(private_key, buffer)#
Decrypts buffer
with private_key
.
private_key
can be an object or a string. If private_key
is a string, it is
treated as the key with no passphrase and will use RSA_PKCS1_OAEP_PADDING
.
If private_key
is an object, it is interpreted as a hash object with the
keys:
key
: <string> - PEM encoded private keypassphrase
: <string> - Optional passphrase for the private keypadding
: An optional padding value, one of the following:crypto.constants.RSA_NO_PADDING
crypto.constants.RSA_PKCS1_PADDING
crypto.constants.RSA_PKCS1_OAEP_PADDING
All paddings are defined in crypto.constants
.
crypto.timingSafeEqual(a, b)#
This function is based on a constant-time algorithm.
Returns true if a
is equal to b
, without leaking timing information that
would allow an attacker to guess one of the values. This is suitable for
comparing HMAC digests or secret values like authentication cookies or
capability urls.
a
and b
must both be Buffer
s, and they must have the same length.
Note: Use of crypto.timingSafeEqual
does not guarantee that the
surrounding code is timing-safe. Care should be taken to ensure that the
surrounding code does not introduce timing vulnerabilities.
crypto.privateEncrypt(private_key, buffer)#
Encrypts buffer
with private_key
.
private_key
can be an object or a string. If private_key
is a string, it is
treated as the key with no passphrase and will use RSA_PKCS1_PADDING
.
If private_key
is an object, it is interpreted as a hash object with the
keys:
key
: <string> - PEM encoded private keypassphrase
: <string> - Optional passphrase for the private keypadding
: An optional padding value, one of the following:crypto.constants.RSA_NO_PADDING
crypto.constants.RSA_PKCS1_PADDING
All paddings are defined in crypto.constants
.
crypto.publicDecrypt(public_key, buffer)#
Decrypts buffer
with public_key
.
public_key
can be an object or a string. If public_key
is a string, it is
treated as the key with no passphrase and will use RSA_PKCS1_PADDING
.
If public_key
is an object, it is interpreted as a hash object with the
keys:
key
: <string> - PEM encoded public keypassphrase
: <string> - Optional passphrase for the private keypadding
: An optional padding value, one of the following:crypto.constants.RSA_NO_PADDING
crypto.constants.RSA_PKCS1_PADDING
crypto.constants.RSA_PKCS1_OAEP_PADDING
Because RSA public keys can be derived from private keys, a private key may be passed instead of a public key.
All paddings are defined in crypto.constants
.
crypto.publicEncrypt(public_key, buffer)#
Encrypts buffer
with public_key
.
public_key
can be an object or a string. If public_key
is a string, it is
treated as the key with no passphrase and will use RSA_PKCS1_OAEP_PADDING
.
If public_key
is an object, it is interpreted as a hash object with the
keys:
key
: <string> - PEM encoded public keypassphrase
: <string> - Optional passphrase for the private keypadding
: An optional padding value, one of the following:crypto.constants.RSA_NO_PADDING
crypto.constants.RSA_PKCS1_PADDING
crypto.constants.RSA_PKCS1_OAEP_PADDING
Because RSA public keys can be derived from private keys, a private key may be passed instead of a public key.
All paddings are defined in crypto.constants
.
crypto.randomBytes(size[, callback])#
Generates cryptographically strong pseudo-random data. The size
argument
is a number indicating the number of bytes to generate.
If a callback
function is provided, the bytes are generated asynchronously
and the callback
function is invoked with two arguments: err
and buf
.
If an error occurs, err
will be an Error object; otherwise it is null. The
buf
argument is a Buffer
containing the generated bytes.
// Asynchronous
const crypto = require('crypto');
crypto.randomBytes(256, (err, buf) => {
if (err) throw err;
console.log(`${buf.length} bytes of random data: ${buf.toString('hex')}`);
});
If the callback
function is not provided, the random bytes are generated
synchronously and returned as a Buffer
. An error will be thrown if
there is a problem generating the bytes.
// Synchronous
const buf = crypto.randomBytes(256);
console.log(
`${buf.length} bytes of random data: ${buf.toString('hex')}`);
The crypto.randomBytes()
method will not complete until there is
sufficient entropy available.
This should normally never take longer than a few milliseconds. The only time
when generating the random bytes may conceivably block for a longer period of
time is right after boot, when the whole system is still low on entropy.
crypto.randomFillSync(buffer[, offset][, size])#
buffer
<Buffer> | <Uint8Array> Must be supplied.offset
<number> Defaults to0
.size
<number> Defaults tobuffer.length - offset
.
Synchronous version of crypto.randomFill()
.
Returns buffer
const buf = Buffer.alloc(10);
console.log(crypto.randomFillSync(buf).toString('hex'));
crypto.randomFillSync(buf, 5);
console.log(buf.toString('hex'));
// The above is equivalent to the following:
crypto.randomFillSync(buf, 5, 5);
console.log(buf.toString('hex'));
crypto.randomFill(buffer[, offset][, size], callback)#
buffer
<Buffer> | <Uint8Array> Must be supplied.offset
<number> Defaults to0
.size
<number> Defaults tobuffer.length - offset
.callback
<Function>function(err, buf) {}
.
This function is similar to crypto.randomBytes()
but requires the first
argument to be a Buffer
that will be filled. It also
requires that a callback is passed in.
If the callback
function is not provided, an error will be thrown.
const buf = Buffer.alloc(10);
crypto.randomFill(buf, (err, buf) => {
if (err) throw err;
console.log(buf.toString('hex'));
});
crypto.randomFill(buf, 5, (err, buf) => {
if (err) throw err;
console.log(buf.toString('hex'));
});
// The above is equivalent to the following:
crypto.randomFill(buf, 5, 5, (err, buf) => {
if (err) throw err;
console.log(buf.toString('hex'));
});
crypto.setEngine(engine[, flags])#
Load and set the engine
for some or all OpenSSL functions (selected by flags).
engine
could be either an id or a path to the engine's shared library.
The optional flags
argument uses ENGINE_METHOD_ALL
by default. The flags
is a bit field taking one of or a mix of the following flags (defined in
crypto.constants
):
crypto.constants.ENGINE_METHOD_RSA
crypto.constants.ENGINE_METHOD_DSA
crypto.constants.ENGINE_METHOD_DH
crypto.constants.ENGINE_METHOD_RAND
crypto.constants.ENGINE_METHOD_ECDH
crypto.constants.ENGINE_METHOD_ECDSA
crypto.constants.ENGINE_METHOD_CIPHERS
crypto.constants.ENGINE_METHOD_DIGESTS
crypto.constants.ENGINE_METHOD_STORE
crypto.constants.ENGINE_METHOD_PKEY_METHS
crypto.constants.ENGINE_METHOD_PKEY_ASN1_METHS
crypto.constants.ENGINE_METHOD_ALL
crypto.constants.ENGINE_METHOD_NONE
Notes#
Legacy Streams API (pre Node.js v0.10)#
The Crypto module was added to Node.js before there was the concept of a
unified Stream API, and before there were Buffer
objects for handling
binary data. As such, the many of the crypto
defined classes have methods not
typically found on other Node.js classes that implement the streams
API (e.g. update()
, final()
, or digest()
). Also, many methods accepted
and returned 'latin1'
encoded strings by default rather than Buffers. This
default was changed after Node.js v0.8 to use Buffer
objects by default
instead.
Recent ECDH Changes#
Usage of ECDH
with non-dynamically generated key pairs has been simplified.
Now, ecdh.setPrivateKey()
can be called with a preselected private key
and the associated public point (key) will be computed and stored in the object.
This allows code to only store and provide the private part of the EC key pair.
ecdh.setPrivateKey()
now also validates that the private key is valid for
the selected curve.
The ecdh.setPublicKey()
method is now deprecated as its inclusion in the
API is not useful. Either a previously stored private key should be set, which
automatically generates the associated public key, or ecdh.generateKeys()
should be called. The main drawback of using ecdh.setPublicKey()
is that
it can be used to put the ECDH key pair into an inconsistent state.
Support for weak or compromised algorithms#
The crypto
module still supports some algorithms which are already
compromised and are not currently recommended for use. The API also allows
the use of ciphers and hashes with a small key size that are considered to be
too weak for safe use.
Users should take full responsibility for selecting the crypto algorithm and key size according to their security requirements.
Based on the recommendations of NIST SP 800-131A:
- MD5 and SHA-1 are no longer acceptable where collision resistance is required such as digital signatures.
- The key used with RSA, DSA and DH algorithms is recommended to have at least 2048 bits and that of the curve of ECDSA and ECDH at least 224 bits, to be safe to use for several years.
- The DH groups of
modp1
,modp2
andmodp5
have a key size smaller than 2048 bits and are not recommended.
See the reference for other recommendations and details.
Crypto Constants#
The following constants exported by crypto.constants
apply to various uses of
the crypto
, tls
, and https
modules and are generally specific to OpenSSL.
OpenSSL Options#
Constant | Description |
---|---|
SSL_OP_ALL |
Applies multiple bug workarounds within OpenSSL. See https://www.openssl.org/docs/man1.0.2/ssl/SSL_CTX_set_options.html for detail. |
SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION |
Allows legacy insecure renegotiation between OpenSSL and unpatched clients or servers. See https://www.openssl.org/docs/man1.0.2/ssl/SSL_CTX_set_options.html. |
SSL_OP_CIPHER_SERVER_PREFERENCE |
Attempts to use the server's preferences instead of the client's when selecting a cipher. Behavior depends on protocol version. See https://www.openssl.org/docs/man1.0.2/ssl/SSL_CTX_set_options.html. |
SSL_OP_CISCO_ANYCONNECT |
Instructs OpenSSL to use Cisco's "speshul" version of DTLS_BAD_VER. |
SSL_OP_COOKIE_EXCHANGE |
Instructs OpenSSL to turn on cookie exchange. |
SSL_OP_CRYPTOPRO_TLSEXT_BUG |
Instructs OpenSSL to add server-hello extension from an early version of the cryptopro draft. |
SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS |
Instructs OpenSSL to disable a SSL 3.0/TLS 1.0 vulnerability workaround added in OpenSSL 0.9.6d. |
SSL_OP_EPHEMERAL_RSA |
Instructs OpenSSL to always use the tmp_rsa key when performing RSA operations. |
SSL_OP_LEGACY_SERVER_CONNECT |
Allows initial connection to servers that do not support RI. |
SSL_OP_MICROSOFT_BIG_SSLV3_BUFFER |
|
SSL_OP_MICROSOFT_SESS_ID_BUG |
|
SSL_OP_MSIE_SSLV2_RSA_PADDING |
Instructs OpenSSL to disable the workaround for a man-in-the-middle protocol-version vulnerability in the SSL 2.0 server implementation. |
SSL_OP_NETSCAPE_CA_DN_BUG |
|
SSL_OP_NETSCAPE_CHALLENGE_BUG |
|
SSL_OP_NETSCAPE_DEMO_CIPHER_CHANGE_BUG |
|
SSL_OP_NETSCAPE_REUSE_CIPHER_CHANGE_BUG |
|
SSL_OP_NO_COMPRESSION |
Instructs OpenSSL to disable support for SSL/TLS compression. |
SSL_OP_NO_QUERY_MTU |
|
SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION |
Instructs OpenSSL to always start a new session when performing renegotiation. |
SSL_OP_NO_SSLv2 |
Instructs OpenSSL to turn off SSL v2 |
SSL_OP_NO_SSLv3 |
Instructs OpenSSL to turn off SSL v3 |
SSL_OP_NO_TICKET |
Instructs OpenSSL to disable use of RFC4507bis tickets. |
SSL_OP_NO_TLSv1 |
Instructs OpenSSL to turn off TLS v1 |
SSL_OP_NO_TLSv1_1 |
Instructs OpenSSL to turn off TLS v1.1 |
SSL_OP_NO_TLSv1_2 |
Instructs OpenSSL to turn off TLS v1.2 | SSL_OP_PKCS1_CHECK_1 |
SSL_OP_PKCS1_CHECK_2 |
|
SSL_OP_SINGLE_DH_USE |
Instructs OpenSSL to always create a new key when using temporary/ephemeral DH parameters. |
SSL_OP_SINGLE_ECDH_USE |
Instructs OpenSSL to always create a new key when using temporary/ephemeral ECDH parameters. | SSL_OP_SSLEAY_080_CLIENT_DH_BUG |
SSL_OP_SSLREF2_REUSE_CERT_TYPE_BUG |
|
SSL_OP_TLS_BLOCK_PADDING_BUG |
|
SSL_OP_TLS_D5_BUG |
|
SSL_OP_TLS_ROLLBACK_BUG |
Instructs OpenSSL to disable version rollback attack detection. |
OpenSSL Engine Constants#
Constant | Description |
---|---|
ENGINE_METHOD_RSA |
Limit engine usage to RSA |
ENGINE_METHOD_DSA |
Limit engine usage to DSA |
ENGINE_METHOD_DH |
Limit engine usage to DH |
ENGINE_METHOD_RAND |
Limit engine usage to RAND |
ENGINE_METHOD_ECDH |
Limit engine usage to ECDH |
ENGINE_METHOD_ECDSA |
Limit engine usage to ECDSA |
ENGINE_METHOD_CIPHERS |
Limit engine usage to CIPHERS |
ENGINE_METHOD_DIGESTS |
Limit engine usage to DIGESTS |
ENGINE_METHOD_STORE |
Limit engine usage to STORE |
ENGINE_METHOD_PKEY_METHS |
Limit engine usage to PKEY_METHDS |
ENGINE_METHOD_PKEY_ASN1_METHS |
Limit engine usage to PKEY_ASN1_METHS |
ENGINE_METHOD_ALL |
|
ENGINE_METHOD_NONE |
Other OpenSSL Constants#
Constant | Description |
---|---|
DH_CHECK_P_NOT_SAFE_PRIME |
|
DH_CHECK_P_NOT_PRIME |
|
DH_UNABLE_TO_CHECK_GENERATOR |
|
DH_NOT_SUITABLE_GENERATOR |
|
NPN_ENABLED |
|
ALPN_ENABLED |
|
RSA_PKCS1_PADDING |
|
RSA_SSLV23_PADDING |
|
RSA_NO_PADDING |
|
RSA_PKCS1_OAEP_PADDING |
|
RSA_X931_PADDING |
|
RSA_PKCS1_PSS_PADDING |
|
RSA_PSS_SALTLEN_DIGEST |
Sets the salt length for RSA_PKCS1_PSS_PADDING to the digest size
when signing or verifying. |
RSA_PSS_SALTLEN_MAX_SIGN |
Sets the salt length for RSA_PKCS1_PSS_PADDING to the maximum
permissible value when signing data. |
RSA_PSS_SALTLEN_AUTO |
Causes the salt length for RSA_PKCS1_PSS_PADDING to be determined
automatically when verifying a signature. |
POINT_CONVERSION_COMPRESSED |
|
POINT_CONVERSION_UNCOMPRESSED |
|
POINT_CONVERSION_HYBRID |
Node.js Crypto Constants#
Constant | Description |
---|---|
defaultCoreCipherList |
Specifies the built-in default cipher list used by Node.js. |
defaultCipherList |
Specifies the active default cipher list used by the current Node.js process. |
Debugger#
Node.js includes an out-of-process debugging utility accessible via a
TCP-based protocol and built-in debugging client. To use it, start Node.js
with the debug
argument followed by the path to the script to debug; a prompt
will be displayed indicating successful launch of the debugger:
$ node debug myscript.js
< Debugger listening on [::]:5858
connecting to 127.0.0.1:5858 ... ok
break in /home/indutny/Code/git/indutny/myscript.js:1
> 1 global.x = 5;
2 setTimeout(() => {
3 debugger;
debug>
Node.js's debugger client is not a full-featured debugger, but simple step and inspection are possible.
Inserting the statement debugger;
into the source code of a script will
enable a breakpoint at that position in the code:
// myscript.js
global.x = 5;
setTimeout(() => {
debugger;
console.log('world');
}, 1000);
console.log('hello');
Once the debugger is run, a breakpoint will occur at line 3:
$ node debug myscript.js
< Debugger listening on [::]:5858
connecting to 127.0.0.1:5858 ... ok
break in /home/indutny/Code/git/indutny/myscript.js:1
> 1 global.x = 5;
2 setTimeout(() => {
3 debugger;
debug> cont
< hello
break in /home/indutny/Code/git/indutny/myscript.js:3
1 global.x = 5;
2 setTimeout(() => {
> 3 debugger;
4 console.log('world');
5 }, 1000);
debug> next
break in /home/indutny/Code/git/indutny/myscript.js:4
2 setTimeout(() => {
3 debugger;
> 4 console.log('world');
5 }, 1000);
6 console.log('hello');
debug> repl
Press Ctrl + C to leave debug repl
> x
5
> 2+2
4
debug> next
break in /home/indutny/Code/git/indutny/myscript.js:5
< world
3 debugger;
4 console.log('world');
> 5 }, 1000);
6 console.log('hello');
7
debug> quit
The repl
command allows code to be evaluated remotely. The next
command
steps to the next line. Type help
to see what other commands are available.
Pressing enter
without typing a command will repeat the previous debugger
command.
Watchers#
It is possible to watch expression and variable values while debugging. On every breakpoint, each expression from the watchers list will be evaluated in the current context and displayed immediately before the breakpoint's source code listing.
To begin watching an expression, type watch('my_expression')
. The command
watchers
will print the active watchers. To remove a watcher, type
unwatch('my_expression')
.
Command reference#
Stepping#
cont
,c
- Continue executionnext
,n
- Step nextstep
,s
- Step inout
,o
- Step outpause
- Pause running code (like pause button in Developer Tools)
Breakpoints#
setBreakpoint()
,sb()
- Set breakpoint on current linesetBreakpoint(line)
,sb(line)
- Set breakpoint on specific linesetBreakpoint('fn()')
,sb(...)
- Set breakpoint on a first statement in functions bodysetBreakpoint('script.js', 1)
,sb(...)
- Set breakpoint on first line of script.jsclearBreakpoint('script.js', 1)
,cb(...)
- Clear breakpoint in script.js on line 1
It is also possible to set a breakpoint in a file (module) that is not loaded yet:
$ node debug test/fixtures/break-in-module/main.js
< Debugger listening on [::]:5858
connecting to 127.0.0.1:5858 ... ok
break in test/fixtures/break-in-module/main.js:1
> 1 var mod = require('./mod.js');
2 mod.hello();
3 mod.hello();
debug> setBreakpoint('mod.js', 2)
Warning: script 'mod.js' was not loaded yet.
> 1 var mod = require('./mod.js');
2 mod.hello();
3 mod.hello();
4 debugger;
5
6 });
debug> c
break in test/fixtures/break-in-module/mod.js:2
1 exports.hello = function() {
> 2 return 'hello from module';
3 };
4
debug>
Information#
backtrace
,bt
- Print backtrace of current execution framelist(5)
- List scripts source code with 5 line context (5 lines before and after)watch(expr)
- Add expression to watch listunwatch(expr)
- Remove expression from watch listwatchers
- List all watchers and their values (automatically listed on each breakpoint)repl
- Open debugger's repl for evaluation in debugging script's contextexec expr
- Execute an expression in debugging script's context
Execution control#
run
- Run script (automatically runs on debugger's start)restart
- Restart scriptkill
- Kill script
Various#
scripts
- List all loaded scriptsversion
- Display V8's version
Advanced Usage#
An alternative way of enabling and accessing the debugger is to start
Node.js with the --debug
command-line flag or by signaling an existing
Node.js process with SIGUSR1
.
Once a process has been set in debug mode this way, it can be inspected
using the Node.js debugger by either connecting to the pid
of the running
process or via URI reference to the listening debugger:
node debug -p <pid>
- Connects to the process via thepid
node debug <URI>
- Connects to the process via the URI such as localhost:5858
V8 Inspector Integration for Node.js#
NOTE: This is an experimental feature.
V8 Inspector integration allows attaching Chrome DevTools to Node.js instances for debugging and profiling.
V8 Inspector can be enabled by passing the --inspect
flag when starting a
Node.js application. It is also possible to supply a custom port with that flag,
e.g. --inspect=9222
will accept DevTools connections on port 9222.
To break on the first line of the application code, provide the --debug-brk
flag in addition to --inspect
.
$ node --inspect index.js
Debugger listening on port 9229.
Warning: This is an experimental feature and could change at any time.
To start debugging, open the following URL in Chrome:
chrome-devtools://devtools/remote/serve_file/@60cd6e859b9f557d2312f5bf532f6aec5f284980/inspector.html?experiments=true&v8only=true&ws=127.0.0.1:9229/3a6d0a9e-0707-48f8-a7c6-48f157b67ab5
(In the example above, the UUID 3a6d0a9e-0707-48f8-a7c6-48f157b67ab5 at the end of the URL is generated on the fly, it varies in different debugging sessions.)
UDP / Datagram Sockets#
The dgram
module provides an implementation of UDP Datagram sockets.
const dgram = require('dgram');
const server = dgram.createSocket('udp4');
server.on('error', (err) => {
console.log(`server error:\n${err.stack}`);
server.close();
});
server.on('message', (msg, rinfo) => {
console.log(`server got: ${msg} from ${rinfo.address}:${rinfo.port}`);
});
server.on('listening', () => {
const address = server.address();
console.log(`server listening ${address.address}:${address.port}`);
});
server.bind(41234);
// server listening 0.0.0.0:41234
Class: dgram.Socket#
The dgram.Socket
object is an EventEmitter
that encapsulates the
datagram functionality.
New instances of dgram.Socket
are created using dgram.createSocket()
.
The new
keyword is not to be used to create dgram.Socket
instances.
Event: 'close'#
The 'close'
event is emitted after a socket is closed with close()
.
Once triggered, no new 'message'
events will be emitted on this socket.
Event: 'error'#
exception
<Error>
The 'error'
event is emitted whenever any error occurs. The event handler
function is passed a single Error object.
Event: 'listening'#
The 'listening'
event is emitted whenever a socket begins listening for
datagram messages. This occurs as soon as UDP sockets are created.
Event: 'message'#
The 'message'
event is emitted when a new datagram is available on a socket.
The event handler function is passed two arguments: msg
and rinfo
.
socket.addMembership(multicastAddress[, multicastInterface])#
Tells the kernel to join a multicast group at the given multicastAddress
and
multicastInterface
using the IP_ADD_MEMBERSHIP
socket option. If the
multicastInterface
argument is not specified, the operating system will choose
one interface and will add membership to it. To add membership to every
available interface, call addMembership
multiple times, once per interface.
socket.address()#
Returns an object containing the address information for a socket.
For UDP sockets, this object will contain address
, family
and port
properties.
socket.bind([port][, address][, callback])#
port
<number> Integer.address
<string>callback
<Function> with no parameters. Called when binding is complete.
For UDP sockets, causes the dgram.Socket
to listen for datagram
messages on a named port
and optional address
. If port
is not
specified or is 0
, the operating system will attempt to bind to a
random port. If address
is not specified, the operating system will
attempt to listen on all addresses. Once binding is complete, a
'listening'
event is emitted and the optional callback
function is
called.
Note that specifying both a 'listening'
event listener and passing a
callback
to the socket.bind()
method is not harmful but not very
useful.
A bound datagram socket keeps the Node.js process running to receive datagram messages.
If binding fails, an 'error'
event is generated. In rare case (e.g.
attempting to bind with a closed socket), an Error
may be thrown.
Example of a UDP server listening on port 41234:
const dgram = require('dgram');
const server = dgram.createSocket('udp4');
server.on('error', (err) => {
console.log(`server error:\n${err.stack}`);
server.close();
});
server.on('message', (msg, rinfo) => {
console.log(`server got: ${msg} from ${rinfo.address}:${rinfo.port}`);
});
server.on('listening', () => {
const address = server.address();
console.log(`server listening ${address.address}:${address.port}`);
});
server.bind(41234);
// server listening 0.0.0.0:41234
socket.bind(options[, callback])#
options
<Object> Required. Supports the following properties:callback
<Function>
For UDP sockets, causes the dgram.Socket
to listen for datagram
messages on a named port
and optional address
that are passed as
properties of an options
object passed as the first argument. If
port
is not specified or is 0
, the operating system will attempt
to bind to a random port. If address
is not specified, the operating
system will attempt to listen on all addresses. Once binding is
complete, a 'listening'
event is emitted and the optional callback
function is called.
Note that specifying both a 'listening'
event listener and passing a
callback
to the socket.bind()
method is not harmful but not very
useful.
The options
object may contain an additional exclusive
property that is
use when using dgram.Socket
objects with the cluster
module. When
exclusive
is set to false
(the default), cluster workers will use the same
underlying socket handle allowing connection handling duties to be shared.
When exclusive
is true
, however, the handle is not shared and attempted
port sharing results in an error.
A bound datagram socket keeps the Node.js process running to receive datagram messages.
If binding fails, an 'error'
event is generated. In rare case (e.g.
attempting to bind with a closed socket), an Error
may be thrown.
An example socket listening on an exclusive port is shown below.
socket.bind({
address: 'localhost',
port: 8000,
exclusive: true
});
socket.close([callback])#
Close the underlying socket and stop listening for data on it. If a callback is
provided, it is added as a listener for the 'close'
event.
socket.dropMembership(multicastAddress[, multicastInterface])#
Instructs the kernel to leave a multicast group at multicastAddress
using the
IP_DROP_MEMBERSHIP
socket option. This method is automatically called by the
kernel when the socket is closed or the process terminates, so most apps will
never have reason to call this.
If multicastInterface
is not specified, the operating system will attempt to
drop membership on all valid interfaces.
socket.send(msg, [offset, length,] port, address[, callback])#
msg
<Buffer> | <string> | <array> Message to be sent.offset
<number> Integer. Offset in the buffer where the message starts.length
<number> Integer. Number of bytes in the message.port
<number> Integer. Destination port.address
<string> Destination hostname or IP address.callback
<Function> Called when the message has been sent.
Broadcasts a datagram on the socket. The destination port
and address
must
be specified.
The msg
argument contains the message to be sent.
Depending on its type, different behavior can apply. If msg
is a Buffer
,
the offset
and length
specify the offset within the Buffer
where the
message begins and the number of bytes in the message, respectively.
If msg
is a String
, then it is automatically converted to a Buffer
with 'utf8'
encoding. With messages that
contain multi-byte characters, offset
and length
will be calculated with
respect to byte length and not the character position.
If msg
is an array, offset
and length
must not be specified.
The address
argument is a string. If the value of address
is a host name,
DNS will be used to resolve the address of the host. If the address
is not
specified or is an empty string, '127.0.0.1'
or '::1'
will be used instead.
If the socket has not been previously bound with a call to bind
, the socket
is assigned a random port number and is bound to the "all interfaces" address
('0.0.0.0'
for udp4
sockets, '::0'
for udp6
sockets.)
An optional callback
function may be specified to as a way of reporting
DNS errors or for determining when it is safe to reuse the buf
object.
Note that DNS lookups delay the time to send for at least one tick of the
Node.js event loop.
The only way to know for sure that the datagram has been sent is by using a
callback
. If an error occurs and a callback
is given, the error will be
passed as the first argument to the callback
. If a callback
is not given,
the error is emitted as an 'error'
event on the socket
object.
Offset and length are optional, but if you specify one you would need to
specify the other. Also, they are supported only when the first
argument is a Buffer
.
Example of sending a UDP packet to a random port on localhost
;
const dgram = require('dgram');
const message = Buffer.from('Some bytes');
const client = dgram.createSocket('udp4');
client.send(message, 41234, 'localhost', (err) => {
client.close();
});
Example of sending a UDP packet composed of multiple buffers to a random port on localhost
;
const dgram = require('dgram');
const buf1 = Buffer.from('Some ');
const buf2 = Buffer.from('bytes');
const client = dgram.createSocket('udp4');
client.send([buf1, buf2], 41234, 'localhost', (err) => {
client.close();
});
Sending multiple buffers might be faster or slower depending on your application and operating system: benchmark it. Usually it is faster.
A Note about UDP datagram size
The maximum size of an IPv4/v6
datagram depends on the MTU
(Maximum Transmission Unit) and on the Payload Length
field size.
The
Payload Length
field is16 bits
wide, which means that a normal payload exceed 64K octets including the internet header and data (65,507 bytes = 65,535 − 8 bytes UDP header − 20 bytes IP header); this is generally true for loopback interfaces, but such long datagram messages are impractical for most hosts and networks.The
MTU
is the largest size a given link layer technology can support for datagram messages. For any link,IPv4
mandates a minimumMTU
of68
octets, while the recommendedMTU
for IPv4 is576
(typically recommended as theMTU
for dial-up type applications), whether they arrive whole or in fragments.For
IPv6
, the minimumMTU
is1280
octets, however, the mandatory minimum fragment reassembly buffer size is1500
octets. The value of68
octets is very small, since most current link layer technologies, like Ethernet, have a minimumMTU
of1500
.
It is impossible to know in advance the MTU of each link through which
a packet might travel. Sending a datagram greater than the receiver MTU
will
not work because the packet will get silently dropped without informing the
source that the data did not reach its intended recipient.
socket.setBroadcast(flag)#
flag
<boolean>
Sets or clears the SO_BROADCAST
socket option. When set to true
, UDP
packets may be sent to a local interface's broadcast address.
socket.setMulticastInterface(multicastInterface)#
multicastInterface
<String>
Note: All references to scope in this section are refering to
IPv6 Zone Indices, which are defined by RFC 4007. In string form, an IP
with a scope index is written as 'IP%scope'
where scope is an interface name or
interface number.
Sets the default outgoing multicast interface of the socket to a chosen
interface or back to system interface selection. The multicastInterface
must
be a valid string representation of an IP from the socket's family.
For IPv4 sockets, this should be the IP configured for the desired physical interface. All packets sent to multicast on the socket will be sent on the interface determined by the most recent successful use of this call.
For IPv6 sockets, multicastInterface
should include a scope to indicate the
interface as in the examples that follow. In IPv6, individual send
calls can
also use explicit scope in addresses, so only packets sent to a multicast
address without specifying an explicit scope are affected by the most recent
successful use of this call.
Examples: IPv6 Outgoing Multicast Interface#
On most systems, where scope format uses the interface name:
const socket = dgram.createSocket('udp6');
socket.bind(1234, () => {
socket.setMulticastInterface('::%eth1');
});
On Windows, where scope format uses an interface number:
const socket = dgram.createSocket('udp6');
socket.bind(1234, () => {
socket.setMulticastInterface('::%2');
});
Example: IPv4 Outgoing Multicast Interface#
All systems use an IP of the host on the desired physical interface:
const socket = dgram.createSocket('udp4');
socket.bind(1234, () => {
socket.setMulticastInterface('10.0.0.2');
});
Call Results#
A call on a socket that is not ready to send or no longer open may throw a Not
running Error
.
If multicastInterface
can not be parsed into an IP then an EINVAL
System Error
is thrown.
On IPv4, if multicastInterface
is a valid address but does not match any
interface, or if the address does not match the family then
a System Error
such as EADDRNOTAVAIL
or EPROTONOSUP
is thrown.
On IPv6, most errors with specifying or omiting scope will result in the socket continuing to use (or returning to) the system's default interface selection.
A socket's address family's ANY address (IPv4 '0.0.0.0'
or IPv6 '::'
) can be
used to return control of the sockets default outgoing interface to the system
for future multicast packets.
socket.setMulticastLoopback(flag)#
flag
<boolean>
Sets or clears the IP_MULTICAST_LOOP
socket option. When set to true
,
multicast packets will also be received on the local interface.
socket.setMulticastTTL(ttl)#
ttl
<number> Integer.
Sets the IP_MULTICAST_TTL
socket option. While TTL generally stands for
"Time to Live", in this context it specifies the number of IP hops that a
packet is allowed to travel through, specifically for multicast traffic. Each
router or gateway that forwards a packet decrements the TTL. If the TTL is
decremented to 0 by a router, it will not be forwarded.
The argument passed to to socket.setMulticastTTL()
is a number of hops
between 0 and 255. The default on most systems is 1
but can vary.
socket.setTTL(ttl)#
ttl
<number> Integer.
Sets the IP_TTL
socket option. While TTL generally stands for "Time to Live",
in this context it specifies the number of IP hops that a packet is allowed to
travel through. Each router or gateway that forwards a packet decrements the
TTL. If the TTL is decremented to 0 by a router, it will not be forwarded.
Changing TTL values is typically done for network probes or when multicasting.
The argument to socket.setTTL()
is a number of hops between 1 and 255.
The default on most systems is 64 but can vary.
socket.ref()#
By default, binding a socket will cause it to block the Node.js process from
exiting as long as the socket is open. The socket.unref()
method can be used
to exclude the socket from the reference counting that keeps the Node.js
process active. The socket.ref()
method adds the socket back to the reference
counting and restores the default behavior.
Calling socket.ref()
multiples times will have no additional effect.
The socket.ref()
method returns a reference to the socket so calls can be
chained.
socket.unref()#
By default, binding a socket will cause it to block the Node.js process from
exiting as long as the socket is open. The socket.unref()
method can be used
to exclude the socket from the reference counting that keeps the Node.js
process active, allowing the process to exit even if the socket is still
listening.
Calling socket.unref()
multiple times will have no addition effect.
The socket.unref()
method returns a reference to the socket so calls can be
chained.
Change to asynchronous socket.bind()
behavior#
As of Node.js v0.10, dgram.Socket#bind()
changed to an asynchronous
execution model. Legacy code that assumes synchronous behavior, as in the
following example:
const s = dgram.createSocket('udp4');
s.bind(1234);
s.addMembership('224.0.0.114');
Must be changed to pass a callback function to the dgram.Socket#bind()
function:
const s = dgram.createSocket('udp4');
s.bind(1234, () => {
s.addMembership('224.0.0.114');
});
dgram
module functions#
dgram.createSocket(options[, callback])#
options
<Object>callback
<Function> Attached as a listener to'message'
events.- Returns: <dgram.Socket>
Creates a dgram.Socket
object. The options
argument is an object that
should contain a type
field of either udp4
or udp6
and an optional
boolean reuseAddr
field.
When reuseAddr
is true
socket.bind()
will reuse the address, even if
another process has already bound a socket on it. reuseAddr
defaults to
false
. The optional callback
function is added as a listener for 'message'
events.
Once the socket is created, calling socket.bind()
will instruct the
socket to begin listening for datagram messages. When address
and port
are
not passed to socket.bind()
the method will bind the socket to the "all
interfaces" address on a random port (it does the right thing for both udp4
and udp6
sockets). The bound address and port can be retrieved using
socket.address().address
and socket.address().port
.
dgram.createSocket(type[, callback])#
type
<string> - Either 'udp4' or 'udp6'.callback
<Function> - Attached as a listener to'message'
events.- Returns: <dgram.Socket>
Creates a dgram.Socket
object of the specified type
. The type
argument
can be either udp4
or udp6
. An optional callback
function can be passed
which is added as a listener for 'message'
events.
Once the socket is created, calling socket.bind()
will instruct the
socket to begin listening for datagram messages. When address
and port
are
not passed to socket.bind()
the method will bind the socket to the "all
interfaces" address on a random port (it does the right thing for both udp4
and udp6
sockets). The bound address and port can be retrieved using
socket.address().address
and socket.address().port
.
DNS#
The dns
module contains functions belonging to two different categories:
1) Functions that use the underlying operating system facilities to perform
name resolution, and that do not necessarily perform any network communication.
This category contains only one function: dns.lookup()
. Developers
looking to perform name resolution in the same way that other applications on
the same operating system behave should use dns.lookup()
.
For example, looking up iana.org
.
const dns = require('dns');
dns.lookup('nodejs.org', (err, addresses, family) => {
console.log('addresses:', addresses);
});
// address: "192.0.43.8" family: IPv4
2) Functions that connect to an actual DNS server to perform name resolution,
and that always use the network to perform DNS queries. This category
contains all functions in the dns
module except dns.lookup()
. These
functions do not use the same set of configuration files used by
dns.lookup()
(e.g. /etc/hosts
). These functions should be used by
developers who do not want to use the underlying operating system's facilities
for name resolution, and instead want to always perform DNS queries.
Below is an example that resolves 'archive.org'
then reverse resolves the IP
addresses that are returned.
const dns = require('dns');
dns.resolve4('archive.org', (err, addresses) => {
if (err) throw err;
console.log(`addresses: ${JSON.stringify(addresses)}`);
addresses.forEach((a) => {
dns.reverse(a, (err, hostnames) => {
if (err) {
throw err;
}
console.log(`reverse for ${a}: ${JSON.stringify(hostnames)}`);
});
});
});
There are subtle consequences in choosing one over the other, please consult the Implementation considerations section for more information.
dns.getServers()#
Returns an array of IP address strings that are being used for name resolution.
dns.lookup(hostname[, options], callback)#
Resolves a hostname (e.g. 'nodejs.org'
) into the first found A (IPv4) or
AAAA (IPv6) record. options
can be an object or integer. If options
is
not provided, then IPv4 and IPv6 addresses are both valid. If options
is
an integer, then it must be 4
or 6
.
Alternatively, options
can be an object containing these properties:
family
<number> - The record family. If present, must be the integer4
or6
. If not provided, both IP v4 and v6 addresses are accepted.hints
: <number> - If present, it should be one or more of the supportedgetaddrinfo
flags. Ifhints
is not provided, then no flags are passed togetaddrinfo
. Multiple flags can be passed throughhints
by bitwiseOR
ing their values. See supportedgetaddrinfo
flags for more information on supported flags.all
: <boolean> - Whentrue
, the callback returns all resolved addresses in an array, otherwise returns a single address. Defaults tofalse
.
All properties are optional.
The callback
function has arguments (err, address, family)
. address
is a
string representation of an IPv4 or IPv6 address. family
is either the
integer 4
or 6
and denotes the family of address
(not necessarily the
value initially passed to lookup
).
With the all
option set to true
, the arguments change to
(err, addresses)
, with addresses
being an array of objects with the
properties address
and family
.
On error, err
is an Error
object, where err.code
is the error code.
Keep in mind that err.code
will be set to 'ENOENT'
not only when
the hostname does not exist but also when the lookup fails in other ways
such as no available file descriptors.
dns.lookup()
does not necessarily have anything to do with the DNS protocol.
The implementation uses an operating system facility that can associate names
with addresses, and vice versa. This implementation can have subtle but
important consequences on the behavior of any Node.js program. Please take some
time to consult the Implementation considerations section before using
dns.lookup()
.
Example usage:
const dns = require('dns');
const options = {
family: 6,
hints: dns.ADDRCONFIG | dns.V4MAPPED,
};
dns.lookup('example.com', options, (err, address, family) =>
console.log('address: %j family: IPv%s', address, family));
// address: "2606:2800:220:1:248:1893:25c8:1946" family: IPv6
// When options.all is true, the result will be an Array.
options.all = true;
dns.lookup('example.com', options, (err, addresses) =>
console.log('addresses: %j', addresses));
// addresses: [{"address":"2606:2800:220:1:248:1893:25c8:1946","family":6}]
Supported getaddrinfo flags#
The following flags can be passed as hints to dns.lookup()
.
dns.ADDRCONFIG
: Returned address types are determined by the types of addresses supported by the current system. For example, IPv4 addresses are only returned if the current system has at least one IPv4 address configured. Loopback addresses are not considered.dns.V4MAPPED
: If the IPv6 family was specified, but no IPv6 addresses were found, then return IPv4 mapped IPv6 addresses. Note that it is not supported on some operating systems (e.g FreeBSD 10.1).
dns.lookupService(address, port, callback)#
Resolves the given address
and port
into a hostname and service using
the operating system's underlying getnameinfo
implementation.
If address
is not a valid IP address, a TypeError
will be thrown.
The port
will be coerced to a number. If it is not a legal port, a TypeError
will be thrown.
The callback has arguments (err, hostname, service)
. The hostname
and
service
arguments are strings (e.g. 'localhost'
and 'http'
respectively).
On error, err
is an Error
object, where err.code
is the error code.
const dns = require('dns');
dns.lookupService('127.0.0.1', 22, (err, hostname, service) => {
console.log(hostname, service);
// Prints: localhost ssh
});
dns.resolve(hostname[, rrtype], callback)#
hostname
<string> Hostname to resolve.rrtype
<string> Resource record type. Default:'A'
.callback
<Function>err
<Error>records
<string[]> | <Object[]> | <string[][]> | <Object>
Uses the DNS protocol to resolve a hostname (e.g. 'nodejs.org'
) into an array
of the resource records. The callback
function has arguments
(err, records)
. When successful, records
will be an array of resource
records. The type and structure of individual results varies based on rrtype
:
rrtype |
records contains |
Result type | Shorthand method |
---|---|---|---|
'A' |
IPv4 addresses (default) | <string> | dns.resolve4() |
'AAAA' |
IPv6 addresses | <string> | dns.resolve6() |
'CNAME' |
canonical name records | <string> | dns.resolveCname() |
'MX' |
mail exchange records | <Object> | dns.resolveMx() |
'NAPTR' |
name authority pointer records | <Object> | dns.resolveNaptr() |
'NS' |
name server records | <string> | dns.resolveNs() |
'PTR' |
pointer records | <string> | dns.resolvePtr() |
'SOA' |
start of authority records | <Object> | dns.resolveSoa() |
'SRV' |
service records | <Object> | dns.resolveSrv() |
'TXT' |
text records | <string[]> | dns.resolveTxt() |
On error, err
is an Error
object, where err.code
is one of the
DNS error codes.
dns.resolve4(hostname[, options], callback)#
Uses the DNS protocol to resolve a IPv4 addresses (A
records) for the
hostname
. The addresses
argument passed to the callback
function
will contain an array of IPv4 addresses (e.g.
['74.125.79.104', '74.125.79.105', '74.125.79.106']
).
hostname
<string> Hostname to resolve.options
<Object>ttl
<boolean> Retrieve the Time-To-Live value (TTL) of each record. The callback receives an array of{ address: '1.2.3.4', ttl: 60 }
objects rather than an array of strings. The TTL is expressed in seconds.
callback
<Function> An(err, result)
callback function.
dns.resolve6(hostname[, options], callback)#
Uses the DNS protocol to resolve a IPv6 addresses (AAAA
records) for the
hostname
. The addresses
argument passed to the callback
function
will contain an array of IPv6 addresses.
hostname
<string> Hostname to resolve.options
<Object>ttl
<boolean> Retrieve the Time-To-Live value (TTL) of each record. The callback receives an array of{ address: '0:1:2:3:4:5:6:7', ttl: 60 }
objects rather than an array of strings. The TTL is expressed in seconds.
callback
<Function> An(err, result)
callback function.
dns.resolveCname(hostname, callback)#
Uses the DNS protocol to resolve CNAME
records for the hostname
. The
addresses
argument passed to the callback
function
will contain an array of canonical name records available for the hostname
(e.g. ['bar.example.com']
).
dns.resolveMx(hostname, callback)#
Uses the DNS protocol to resolve mail exchange records (MX
records) for the
hostname
. The addresses
argument passed to the callback
function will
contain an array of objects containing both a priority
and exchange
property (e.g. [{priority: 10, exchange: 'mx.example.com'}, ...]
).
dns.resolveNaptr(hostname, callback)#
Uses the DNS protocol to resolve regular expression based records (NAPTR
records) for the hostname
. The callback
function has arguments
(err, addresses)
. The addresses
argument passed to the callback
function
will contain an array of objects with the following properties:
flags
service
regexp
replacement
order
preference
For example:
{
flags: 's',
service: 'SIP+D2U',
regexp: '',
replacement: '_sip._udp.example.com',
order: 30,
preference: 100
}
dns.resolveNs(hostname, callback)#
Uses the DNS protocol to resolve name server records (NS
records) for the
hostname
. The addresses
argument passed to the callback
function will
contain an array of name server records available for hostname
(e.g. ['ns1.example.com', 'ns2.example.com']
).
dns.resolveSoa(hostname, callback)#
Uses the DNS protocol to resolve a start of authority record (SOA
record) for
the hostname
. The addresses
argument passed to the callback
function will
be an object with the following properties:
nsname
hostmaster
serial
refresh
retry
expire
minttl
{
nsname: 'ns.example.com',
hostmaster: 'root.example.com',
serial: 2013101809,
refresh: 10000,
retry: 2400,
expire: 604800,
minttl: 3600
}
dns.resolveSrv(hostname, callback)#
Uses the DNS protocol to resolve service records (SRV
records) for the
hostname
. The addresses
argument passed to the callback
function will
be an array of objects with the following properties:
priority
weight
port
name
{
priority: 10,
weight: 5,
port: 21223,
name: 'service.example.com'
}
dns.resolvePtr(hostname, callback)#
Uses the DNS protocol to resolve pointer records (PTR
records) for the
hostname
. The addresses
argument passed to the callback
function will
be an array of strings containing the reply records.
dns.resolveTxt(hostname, callback)#
hostname
<string>callback
<Function>err
<Error>records
<string[][]>
Uses the DNS protocol to resolve text queries (TXT
records) for the
hostname
. The records
argument passed to the callback
function is a
two-dimensional array of the text records available for hostname
(e.g.,
[ ['v=spf1 ip4:0.0.0.0 ', '~all' ] ]
). Each sub-array contains TXT chunks of
one record. Depending on the use case, these could be either joined together or
treated separately.
dns.reverse(ip, callback)#
Performs a reverse DNS query that resolves an IPv4 or IPv6 address to an array of hostnames.
The callback
function has arguments (err, hostnames)
, where hostnames
is an array of resolved hostnames for the given ip
.
On error, err
is an Error
object, where err.code
is
one of the DNS error codes.
dns.setServers(servers)#
Sets the IP addresses of the servers to be used when resolving. The servers
argument is an array of IPv4 or IPv6 addresses.
If a port specified on the address it will be removed.
An error will be thrown if an invalid address is provided.
The dns.setServers()
method must not be called while a DNS query is in
progress.
Error codes#
Each DNS query can return one of the following error codes:
dns.NODATA
: DNS server returned answer with no data.dns.FORMERR
: DNS server claims query was misformatted.dns.SERVFAIL
: DNS server returned general failure.dns.NOTFOUND
: Domain name not found.dns.NOTIMP
: DNS server does not implement requested operation.dns.REFUSED
: DNS server refused query.dns.BADQUERY
: Misformatted DNS query.dns.BADNAME
: Misformatted hostname.dns.BADFAMILY
: Unsupported address family.dns.BADRESP
: Misformatted DNS reply.dns.CONNREFUSED
: Could not contact DNS servers.dns.TIMEOUT
: Timeout while contacting DNS servers.dns.EOF
: End of file.dns.FILE
: Error reading file.dns.NOMEM
: Out of memory.dns.DESTRUCTION
: Channel is being destroyed.dns.BADSTR
: Misformatted string.dns.BADFLAGS
: Illegal flags specified.dns.NONAME
: Given hostname is not numeric.dns.BADHINTS
: Illegal hints flags specified.dns.NOTINITIALIZED
: c-ares library initialization not yet performed.dns.LOADIPHLPAPI
: Error loading iphlpapi.dll.dns.ADDRGETNETWORKPARAMS
: Could not find GetNetworkParams function.dns.CANCELLED
: DNS query cancelled.
Implementation considerations#
Although dns.lookup()
and the various dns.resolve*()/dns.reverse()
functions have the same goal of associating a network name with a network
address (or vice versa), their behavior is quite different. These differences
can have subtle but significant consequences on the behavior of Node.js
programs.
dns.lookup()
#
Under the hood, dns.lookup()
uses the same operating system facilities
as most other programs. For instance, dns.lookup()
will almost always
resolve a given name the same way as the ping
command. On most POSIX-like
operating systems, the behavior of the dns.lookup()
function can be
modified by changing settings in nsswitch.conf(5) and/or resolv.conf(5),
but note that changing these files will change the behavior of all other
programs running on the same operating system.
Though the call to dns.lookup()
will be asynchronous from JavaScript's
perspective, it is implemented as a synchronous call to getaddrinfo(3) that
runs on libuv's threadpool. Because libuv's threadpool has a fixed size, it
means that if for whatever reason the call to getaddrinfo(3) takes a long
time, other operations that could run on libuv's threadpool (such as filesystem
operations) will experience degraded performance. In order to mitigate this
issue, one potential solution is to increase the size of libuv's threadpool by
setting the 'UV_THREADPOOL_SIZE'
environment variable to a value greater than
4
(its current default value). For more information on libuv's threadpool, see
the official libuv documentation.
dns.resolve()
, dns.resolve*()
and dns.reverse()
#
These functions are implemented quite differently than dns.lookup()
. They
do not use getaddrinfo(3) and they always perform a DNS query on the
network. This network communication is always done asynchronously, and does not
use libuv's threadpool.
As a result, these functions cannot have the same negative impact on other
processing that happens on libuv's threadpool that dns.lookup()
can have.
They do not use the same set of configuration files than what dns.lookup()
uses. For instance, they do not use the configuration from /etc/hosts
.
Domain#
This module is pending deprecation. Once a replacement API has been finalized, this module will be fully deprecated. Most end users should not have cause to use this module. Users who absolutely must have the functionality that domains provide may rely on it for the time being but should expect to have to migrate to a different solution in the future.
Domains provide a way to handle multiple different IO operations as a
single group. If any of the event emitters or callbacks registered to a
domain emit an 'error'
event, or throw an error, then the domain object
will be notified, rather than losing the context of the error in the
process.on('uncaughtException')
handler, or causing the program to
exit immediately with an error code.
Warning: Don't Ignore Errors!#
Domain error handlers are not a substitute for closing down your process when an error occurs.
By the very nature of how throw
works in JavaScript, there is almost
never any way to safely "pick up where you left off", without leaking
references, or creating some other sort of undefined brittle state.
The safest way to respond to a thrown error is to shut down the process. Of course, in a normal web server, you might have many connections open, and it is not reasonable to abruptly shut those down because an error was triggered by someone else.
The better approach is to send an error response to the request that triggered the error, while letting the others finish in their normal time, and stop listening for new requests in that worker.
In this way, domain
usage goes hand-in-hand with the cluster module,
since the master process can fork a new worker when a worker
encounters an error. For Node.js programs that scale to multiple
machines, the terminating proxy or service registry can take note of
the failure, and react accordingly.
For example, this is not a good idea:
// XXX WARNING! BAD IDEA!
const d = require('domain').create();
d.on('error', (er) => {
// The error won't crash the process, but what it does is worse!
// Though we've prevented abrupt process restarting, we are leaking
// resources like crazy if this ever happens.
// This is no better than process.on('uncaughtException')!
console.log(`error, but oh well ${er.message}`);
});
d.run(() => {
require('http').createServer((req, res) => {
handleRequest(req, res);
}).listen(PORT);
});
By using the context of a domain, and the resilience of separating our program into multiple worker processes, we can react more appropriately, and handle errors with much greater safety.
// Much better!
const cluster = require('cluster');
const PORT = +process.env.PORT || 1337;
if (cluster.isMaster) {
// In real life, you'd probably use more than just 2 workers,
// and perhaps not put the master and worker in the same file.
//
// You can also of course get a bit fancier about logging, and
// implement whatever custom logic you need to prevent DoS
// attacks and other bad behavior.
//
// See the options in the cluster documentation.
//
// The important thing is that the master does very little,
// increasing our resilience to unexpected errors.
cluster.fork();
cluster.fork();
cluster.on('disconnect', (worker) => {
console.error('disconnect!');
cluster.fork();
});
} else {
// the worker
//
// This is where we put our bugs!
const domain = require('domain');
// See the cluster documentation for more details about using
// worker processes to serve requests. How it works, caveats, etc.
const server = require('http').createServer((req, res) => {
const d = domain.create();
d.on('error', (er) => {
console.error(`error ${er.stack}`);
// Note: we're in dangerous territory!
// By definition, something unexpected occurred,
// which we probably didn't want.
// Anything can happen now! Be very careful!
try {
// make sure we close down within 30 seconds
const killtimer = setTimeout(() => {
process.exit(1);
}, 30000);
// But don't keep the process open just for that!
killtimer.unref();
// stop taking new requests.
server.close();
// Let the master know we're dead. This will trigger a
// 'disconnect' in the cluster master, and then it will fork
// a new worker.
cluster.worker.disconnect();
// try to send an error to the request that triggered the problem
res.statusCode = 500;
res.setHeader('content-type', 'text/plain');
res.end('Oops, there was a problem!\n');
} catch (er2) {
// oh well, not much we can do at this point.
console.error(`Error sending 500! ${er2.stack}`);
}
});
// Because req and res were created before this domain existed,
// we need to explicitly add them.
// See the explanation of implicit vs explicit binding below.
d.add(req);
d.add(res);
// Now run the handler function in the domain.
d.run(() => {
handleRequest(req, res);
});
});
server.listen(PORT);
}
// This part is not important. Just an example routing thing.
// You'd put your fancy application logic here.
function handleRequest(req, res) {
switch (req.url) {
case '/error':
// We do some async stuff, and then...
setTimeout(() => {
// Whoops!
flerb.bark();
}, timeout);
break;
default:
res.end('ok');
}
}
Additions to Error objects#
Any time an Error
object is routed through a domain, a few extra fields
are added to it.
error.domain
The domain that first handled the error.error.domainEmitter
The event emitter that emitted an'error'
event with the error object.error.domainBound
The callback function which was bound to the domain, and passed an error as its first argument.error.domainThrown
A boolean indicating whether the error was thrown, emitted, or passed to a bound callback function.
Implicit Binding#
If domains are in use, then all new EventEmitter objects (including Stream objects, requests, responses, etc.) will be implicitly bound to the active domain at the time of their creation.
Additionally, callbacks passed to lowlevel event loop requests (such as to fs.open, or other callback-taking methods) will automatically be bound to the active domain. If they throw, then the domain will catch the error.
In order to prevent excessive memory usage, Domain objects themselves are not implicitly added as children of the active domain. If they were, then it would be too easy to prevent request and response objects from being properly garbage collected.
If you want to nest Domain objects as children of a parent Domain, then you must explicitly add them.
Implicit binding routes thrown errors and 'error'
events to the
Domain's 'error'
event, but does not register the EventEmitter on the
Domain, so domain.dispose()
will not shut down the EventEmitter.
Implicit binding only takes care of thrown errors and 'error'
events.
Explicit Binding#
Sometimes, the domain in use is not the one that ought to be used for a specific event emitter. Or, the event emitter could have been created in the context of one domain, but ought to instead be bound to some other domain.
For example, there could be one domain in use for an HTTP server, but perhaps we would like to have a separate domain to use for each request.
That is possible via explicit binding.
For example:
// create a top-level domain for the server
const domain = require('domain');
const http = require('http');
const serverDomain = domain.create();
serverDomain.run(() => {
// server is created in the scope of serverDomain
http.createServer((req, res) => {
// req and res are also created in the scope of serverDomain
// however, we'd prefer to have a separate domain for each request.
// create it first thing, and add req and res to it.
const reqd = domain.create();
reqd.add(req);
reqd.add(res);
reqd.on('error', (er) => {
console.error('Error', er, req.url);
try {
res.writeHead(500);
res.end('Error occurred, sorry.');
} catch (er2) {
console.error('Error sending 500', er2, req.url);
}
});
}).listen(1337);
});
domain.create()#
- Returns: <Domain>
Returns a new Domain object.
Class: Domain#
The Domain class encapsulates the functionality of routing errors and uncaught exceptions to the active Domain object.
Domain is a child class of EventEmitter
. To handle the errors that it
catches, listen to its 'error'
event.
domain.run(fn[, ...args])#
fn
<Function>...args
<any>
Run the supplied function in the context of the domain, implicitly binding all event emitters, timers, and lowlevel requests that are created in that context. Optionally, arguments can be passed to the function.
This is the most basic way to use a domain.
Example:
const domain = require('domain');
const fs = require('fs');
const d = domain.create();
d.on('error', (er) => {
console.error('Caught error!', er);
});
d.run(() => {
process.nextTick(() => {
setTimeout(() => { // simulating some various async stuff
fs.open('non-existent file', 'r', (er, fd) => {
if (er) throw er;
// proceed...
});
}, 100);
});
});
In this example, the d.on('error')
handler will be triggered, rather
than crashing the program.
domain.members#
An array of timers and event emitters that have been explicitly added to the domain.
domain.add(emitter)#
emitter
<EventEmitter> | <Timer> emitter or timer to be added to the domain
Explicitly adds an emitter to the domain. If any event handlers called by
the emitter throw an error, or if the emitter emits an 'error'
event, it
will be routed to the domain's 'error'
event, just like with implicit
binding.
This also works with timers that are returned from setInterval()
and
setTimeout()
. If their callback function throws, it will be caught by
the domain 'error' handler.
If the Timer or EventEmitter was already bound to a domain, it is removed from that one, and bound to this one instead.
domain.remove(emitter)#
emitter
<EventEmitter> | <Timer> emitter or timer to be removed from the domain
The opposite of domain.add(emitter)
. Removes domain handling from the
specified emitter.
domain.bind(callback)#
callback
<Function> The callback function- Returns: <Function> The bound function
The returned function will be a wrapper around the supplied callback
function. When the returned function is called, any errors that are
thrown will be routed to the domain's 'error'
event.
Example#
const d = domain.create();
function readSomeFile(filename, cb) {
fs.readFile(filename, 'utf8', d.bind((er, data) => {
// if this throws, it will also be passed to the domain
return cb(er, data ? JSON.parse(data) : null);
}));
}
d.on('error', (er) => {
// an error occurred somewhere.
// if we throw it now, it will crash the program
// with the normal line number and stack message.
});
domain.intercept(callback)#
callback
<Function> The callback function- Returns: <Function> The intercepted function
This method is almost identical to domain.bind(callback)
. However, in
addition to catching thrown errors, it will also intercept Error
objects sent as the first argument to the function.
In this way, the common if (err) return callback(err);
pattern can be replaced
with a single error handler in a single place.
Example#
const d = domain.create();
function readSomeFile(filename, cb) {
fs.readFile(filename, 'utf8', d.intercept((data) => {
// note, the first argument is never passed to the
// callback since it is assumed to be the 'Error' argument
// and thus intercepted by the domain.
// if this throws, it will also be passed to the domain
// so the error-handling logic can be moved to the 'error'
// event on the domain instead of being repeated throughout
// the program.
return cb(null, JSON.parse(data));
}));
}
d.on('error', (er) => {
// an error occurred somewhere.
// if we throw it now, it will crash the program
// with the normal line number and stack message.
});
domain.enter()#
The enter
method is plumbing used by the run
, bind
, and intercept
methods to set the active domain. It sets domain.active
and process.domain
to the domain, and implicitly pushes the domain onto the domain stack managed
by the domain module (see domain.exit()
for details on the domain stack). The
call to enter
delimits the beginning of a chain of asynchronous calls and I/O
operations bound to a domain.
Calling enter
changes only the active domain, and does not alter the domain
itself. enter
and exit
can be called an arbitrary number of times on a
single domain.
If the domain on which enter
is called has been disposed, enter
will return
without setting the domain.
domain.exit()#
The exit
method exits the current domain, popping it off the domain stack.
Any time execution is going to switch to the context of a different chain of
asynchronous calls, it's important to ensure that the current domain is exited.
The call to exit
delimits either the end of or an interruption to the chain
of asynchronous calls and I/O operations bound to a domain.
If there are multiple, nested domains bound to the current execution context,
exit
will exit any domains nested within this domain.
Calling exit
changes only the active domain, and does not alter the domain
itself. enter
and exit
can be called an arbitrary number of times on a
single domain.
If the domain on which exit
is called has been disposed, exit
will return
without exiting the domain.
domain.dispose()#
Once dispose
has been called, the domain will no longer be used by callbacks
bound into the domain via run
, bind
, or intercept
, and a 'dispose'
event
is emitted.
Errors#
Applications running in Node.js will generally experience four categories of errors:
- Standard JavaScript errors such as:
- <EvalError> : thrown when a call to
eval()
fails. - <SyntaxError> : thrown in response to improper JavaScript language syntax.
- <RangeError> : thrown when a value is not within an expected range
- <ReferenceError> : thrown when using undefined variables
- <TypeError> : thrown when passing arguments of the wrong type
- <URIError> : thrown when a global URI handling function is misused.
- <EvalError> : thrown when a call to
- System errors triggered by underlying operating system constraints such as attempting to open a file that does not exist, attempting to send data over a closed socket, etc;
- And User-specified errors triggered by application code.
- Assertion Errors are a special class of error that can be triggered whenever
Node.js detects an exceptional logic violation that should never occur. These
are raised typically by the
assert
module.
All JavaScript and System errors raised by Node.js inherit from, or are instances of, the standard JavaScript <Error> class and are guaranteed to provide at least the properties available on that class.
Error Propagation and Interception#
Node.js supports several mechanisms for propagating and handling errors that occur while an application is running. How these errors are reported and handled depends entirely on the type of Error and the style of the API that is called.
All JavaScript errors are handled as exceptions that immediately generate
and throw an error using the standard JavaScript throw
mechanism. These
are handled using the try / catch
construct provided by the JavaScript
language.
// Throws with a ReferenceError because z is undefined
try {
const m = 1;
const n = m + z;
} catch (err) {
// Handle the error here.
}
Any use of the JavaScript throw
mechanism will raise an exception that
must be handled using try / catch
or the Node.js process will exit
immediately.
With few exceptions, Synchronous APIs (any blocking method that does not
accept a callback
function, such as fs.readFileSync
), will use throw
to report errors.
Errors that occur within Asynchronous APIs may be reported in multiple ways:
- Most asynchronous methods that accept a
callback
function will accept anError
object passed as the first argument to that function. If that first argument is notnull
and is an instance ofError
, then an error occurred that should be handled.
const fs = require('fs');
fs.readFile('a file that does not exist', (err, data) => {
if (err) {
console.error('There was an error reading the file!', err);
return;
}
// Otherwise handle the data
});
When an asynchronous method is called on an object that is an
EventEmitter
, errors can be routed to that object's'error'
event.const net = require('net'); const connection = net.connect('localhost'); // Adding an 'error' event handler to a stream: connection.on('error', (err) => { // If the connection is reset by the server, or if it can't // connect at all, or on any sort of error encountered by // the connection, the error will be sent here. console.error(err); }); connection.pipe(process.stdout);
A handful of typically asynchronous methods in the Node.js API may still use the
throw
mechanism to raise exceptions that must be handled usingtry / catch
. There is no comprehensive list of such methods; please refer to the documentation of each method to determine the appropriate error handling mechanism required.
The use of the 'error'
event mechanism is most common for stream-based
and event emitter-based APIs, which themselves represent a series of
asynchronous operations over time (as opposed to a single operation that may
pass or fail).
For all EventEmitter
objects, if an 'error'
event handler is not
provided, the error will be thrown, causing the Node.js process to report an
unhandled exception and crash unless either: The domain
module is used
appropriately or a handler has been registered for the
process.on('uncaughtException')
event.
const EventEmitter = require('events');
const ee = new EventEmitter();
setImmediate(() => {
// This will crash the process because no 'error' event
// handler has been added.
ee.emit('error', new Error('This will crash'));
});
Errors generated in this way cannot be intercepted using try / catch
as
they are thrown after the calling code has already exited.
Developers must refer to the documentation for each method to determine exactly how errors raised by those methods are propagated.
Node.js style callbacks#
Most asynchronous methods exposed by the Node.js core API follow an idiomatic
pattern referred to as a "Node.js style callback". With this pattern, a
callback function is passed to the method as an argument. When the operation
either completes or an error is raised, the callback function is called with
the Error object (if any) passed as the first argument. If no error was raised,
the first argument will be passed as null
.
const fs = require('fs');
function nodeStyleCallback(err, data) {
if (err) {
console.error('There was an error', err);
return;
}
console.log(data);
}
fs.readFile('/some/file/that/does-not-exist', nodeStyleCallback);
fs.readFile('/some/file/that/does-exist', nodeStyleCallback);
The JavaScript try / catch
mechanism cannot be used to intercept errors
generated by asynchronous APIs. A common mistake for beginners is to try to
use throw
inside a Node.js style callback:
// THIS WILL NOT WORK:
const fs = require('fs');
try {
fs.readFile('/some/file/that/does-not-exist', (err, data) => {
// mistaken assumption: throwing here...
if (err) {
throw err;
}
});
} catch (err) {
// This will not catch the throw!
console.error(err);
}
This will not work because the callback function passed to fs.readFile()
is
called asynchronously. By the time the callback has been called, the
surrounding code (including the try { } catch (err) { }
block will have
already exited. Throwing an error inside the callback can crash the Node.js
process in most cases. If domains are enabled, or a handler has been
registered with process.on('uncaughtException')
, such errors can be
intercepted.
Class: Error#
A generic JavaScript Error
object that does not denote any specific
circumstance of why the error occurred. Error
objects capture a "stack trace"
detailing the point in the code at which the Error
was instantiated, and may
provide a text description of the error.
All errors generated by Node.js, including all System and JavaScript errors,
will either be instances of, or inherit from, the Error
class.
new Error(message)#
message
<string>
Creates a new Error
object and sets the error.message
property to the
provided text message. If an object is passed as message
, the text message
is generated by calling message.toString()
. The error.stack
property will
represent the point in the code at which new Error()
was called. Stack traces
are dependent on V8's stack trace API. Stack traces extend only to either
(a) the beginning of synchronous code execution, or (b) the number of frames
given by the property Error.stackTraceLimit
, whichever is smaller.
Error.captureStackTrace(targetObject[, constructorOpt])#
targetObject
<Object>constructorOpt
<Function>
Creates a .stack
property on targetObject
, which when accessed returns
a string representing the location in the code at which
Error.captureStackTrace()
was called.
const myObject = {};
Error.captureStackTrace(myObject);
myObject.stack; // similar to `new Error().stack`
The first line of the trace, instead of being prefixed with ErrorType:
message
, will be the result of calling targetObject.toString()
.
The optional constructorOpt
argument accepts a function. If given, all frames
above constructorOpt
, including constructorOpt
, will be omitted from the
generated stack trace.
The constructorOpt
argument is useful for hiding implementation
details of error generation from an end user. For instance:
function MyError() {
Error.captureStackTrace(this, MyError);
}
// Without passing MyError to captureStackTrace, the MyError
// frame would show up in the .stack property. By passing
// the constructor, we omit that frame, and retain all frames below it.
new MyError().stack;
Error.stackTraceLimit#
The Error.stackTraceLimit
property specifies the number of stack frames
collected by a stack trace (whether generated by new Error().stack
or
Error.captureStackTrace(obj)
).
The default value is 10
but may be set to any valid JavaScript number. Changes
will affect any stack trace captured after the value has been changed.
If set to a non-number value, or set to a negative number, stack traces will not capture any frames.
error.message#
The error.message
property is the string description of the error as set by calling new Error(message)
.
The message
passed to the constructor will also appear in the first line of
the stack trace of the Error
, however changing this property after the
Error
object is created may not change the first line of the stack trace
(for example, when error.stack
is read before this property is changed).
const err = new Error('The message');
console.error(err.message);
// Prints: The message
error.stack#
The error.stack
property is a string describing the point in the code at which
the Error
was instantiated.
For example:
Error: Things keep happening!
at /home/gbusey/file.js:525:2
at Frobnicator.refrobulate (/home/gbusey/business-logic.js:424:21)
at Actor.<anonymous> (/home/gbusey/actors.js:400:8)
at increaseSynergy (/home/gbusey/actors.js:701:6)
The first line is formatted as <error class name>: <error message>
, and
is followed by a series of stack frames (each line beginning with "at ").
Each frame describes a call site within the code that lead to the error being
generated. V8 attempts to display a name for each function (by variable name,
function name, or object method name), but occasionally it will not be able to
find a suitable name. If V8 cannot determine a name for the function, only
location information will be displayed for that frame. Otherwise, the
determined function name will be displayed with location information appended
in parentheses.
It is important to note that frames are only generated for JavaScript
functions. If, for example, execution synchronously passes through a C++ addon
function called cheetahify
, which itself calls a JavaScript function, the
frame representing the cheetahify
call will not be present in the stack
traces:
const cheetahify = require('./native-binding.node');
function makeFaster() {
// cheetahify *synchronously* calls speedy.
cheetahify(function speedy() {
throw new Error('oh no!');
});
}
makeFaster(); // will throw:
// /home/gbusey/file.js:6
// throw new Error('oh no!');
// ^
// Error: oh no!
// at speedy (/home/gbusey/file.js:6:11)
// at makeFaster (/home/gbusey/file.js:5:3)
// at Object.<anonymous> (/home/gbusey/file.js:10:1)
// at Module._compile (module.js:456:26)
// at Object.Module._extensions..js (module.js:474:10)
// at Module.load (module.js:356:32)
// at Function.Module._load (module.js:312:12)
// at Function.Module.runMain (module.js:497:10)
// at startup (node.js:119:16)
// at node.js:906:3
The location information will be one of:
native
, if the frame represents a call internal to V8 (as in[].forEach
).plain-filename.js:line:column
, if the frame represents a call internal to Node.js./absolute/path/to/file.js:line:column
, if the frame represents a call in a user program, or its dependencies.
The string representing the stack trace is lazily generated when the
error.stack
property is accessed.
The number of frames captured by the stack trace is bounded by the smaller of
Error.stackTraceLimit
or the number of available frames on the current event
loop tick.
System-level errors are generated as augmented Error
instances, which are
detailed here.
Class: RangeError#
A subclass of Error
that indicates that a provided argument was not within the
set or range of acceptable values for a function; whether that is a numeric
range, or outside the set of options for a given function parameter.
For example:
require('net').connect(-1);
// throws "RangeError: "port" option should be >= 0 and < 65536: -1"
Node.js will generate and throw RangeError
instances immediately as a form
of argument validation.
Class: ReferenceError#
A subclass of Error
that indicates that an attempt is being made to access a
variable that is not defined. Such errors commonly indicate typos in code, or
an otherwise broken program.
While client code may generate and propagate these errors, in practice, only V8 will do so.
doesNotExist;
// throws ReferenceError, doesNotExist is not a variable in this program.
Unless an application is dynamically generating and running code,
ReferenceError
instances should always be considered a bug in the code
or its dependencies.
Class: SyntaxError#
A subclass of Error
that indicates that a program is not valid JavaScript.
These errors may only be generated and propagated as a result of code
evaluation. Code evaluation may happen as a result of eval
, Function
,
require
, or vm. These errors are almost always indicative of a broken
program.
try {
require('vm').runInThisContext('binary ! isNotOk');
} catch (err) {
// err will be a SyntaxError
}
SyntaxError
instances are unrecoverable in the context that created them –
they may only be caught by other contexts.
Class: TypeError#
A subclass of Error
that indicates that a provided argument is not an
allowable type. For example, passing a function to a parameter which expects a
string would be considered a TypeError.
require('url').parse(() => { });
// throws TypeError, since it expected a string
Node.js will generate and throw TypeError
instances immediately as a form
of argument validation.
Exceptions vs. Errors#
A JavaScript exception is a value that is thrown as a result of an invalid
operation or as the target of a throw
statement. While it is not required
that these values are instances of Error
or classes which inherit from
Error
, all exceptions thrown by Node.js or the JavaScript runtime will be
instances of Error.
Some exceptions are unrecoverable at the JavaScript layer. Such exceptions
will always cause the Node.js process to crash. Examples include assert()
checks or abort()
calls in the C++ layer.
System Errors#
System errors are generated when exceptions occur within the program's runtime environment. Typically, these are operational errors that occur when an application violates an operating system constraint such as attempting to read a file that does not exist or when the user does not have sufficient permissions.
System errors are typically generated at the syscall level: an exhaustive list
of error codes and their meanings is available by running man 2 intro
or
man 3 errno
on most Unices; or online.
In Node.js, system errors are represented as augmented Error
objects with
added properties.
Class: System Error#
error.code#
The error.code
property is a string representing the error code, which is always
E
followed by a sequence of capital letters.
error.errno#
The error.errno
property is a number or a string.
The number is a negative value which corresponds to the error code defined in
libuv Error handling
. See uv-errno.h header file (deps/uv/include/uv-errno.h
in
the Node.js source tree) for details.
In case of a string, it is the same as error.code
.
error.syscall#
The error.syscall
property is a string describing the syscall that failed.
error.path#
When present (e.g. in fs
or child_process
), the error.path
property is a string
containing a relevant invalid pathname.
error.address#
When present (e.g. in net
or dgram
), the error.address
property is a string
describing the address to which the connection failed.
error.port#
When present (e.g. in net
or dgram
), the error.port
property is a number representing
the connection's port that is not available.
Common System Errors#
This list is not exhaustive, but enumerates many of the common system errors encountered when writing a Node.js program. An exhaustive list may be found here.
EACCES
(Permission denied): An attempt was made to access a file in a way forbidden by its file access permissions.EADDRINUSE
(Address already in use): An attempt to bind a server (net
,http
, orhttps
) to a local address failed due to another server on the local system already occupying that address.ECONNREFUSED
(Connection refused): No connection could be made because the target machine actively refused it. This usually results from trying to connect to a service that is inactive on the foreign host.ECONNRESET
(Connection reset by peer): A connection was forcibly closed by a peer. This normally results from a loss of the connection on the remote socket due to a timeout or reboot. Commonly encountered via thehttp
andnet
modules.EEXIST
(File exists): An existing file was the target of an operation that required that the target not exist.EISDIR
(Is a directory): An operation expected a file, but the given pathname was a directory.EMFILE
(Too many open files in system): Maximum number of file descriptors allowable on the system has been reached, and requests for another descriptor cannot be fulfilled until at least one has been closed. This is encountered when opening many files at once in parallel, especially on systems (in particular, macOS) where there is a low file descriptor limit for processes. To remedy a low limit, runulimit -n 2048
in the same shell that will run the Node.js process.ENOENT
(No such file or directory): Commonly raised byfs
operations to indicate that a component of the specified pathname does not exist -- no entity (file or directory) could be found by the given path.ENOTDIR
(Not a directory): A component of the given pathname existed, but was not a directory as expected. Commonly raised byfs.readdir
.ENOTEMPTY
(Directory not empty): A directory with entries was the target of an operation that requires an empty directory -- usuallyfs.unlink
.EPERM
(Operation not permitted): An attempt was made to perform an operation that requires elevated privileges.EPIPE
(Broken pipe): A write on a pipe, socket, or FIFO for which there is no process to read the data. Commonly encountered at thenet
andhttp
layers, indicative that the remote side of the stream being written to has been closed.ETIMEDOUT
(Operation timed out): A connect or send request failed because the connected party did not properly respond after a period of time. Usually encountered byhttp
ornet
-- often a sign that asocket.end()
was not properly called.
Events#
Much of the Node.js core API is built around an idiomatic asynchronous event-driven architecture in which certain kinds of objects (called "emitters") periodically emit named events that cause Function objects ("listeners") to be called.
For instance: a net.Server
object emits an event each time a peer
connects to it; a fs.ReadStream
emits an event when the file is opened;
a stream emits an event whenever data is available to be read.
All objects that emit events are instances of the EventEmitter
class. These
objects expose an eventEmitter.on()
function that allows one or more
functions to be attached to named events emitted by the object. Typically,
event names are camel-cased strings but any valid JavaScript property key
can be used.
When the EventEmitter
object emits an event, all of the functions attached
to that specific event are called synchronously. Any values returned by the
called listeners are ignored and will be discarded.
The following example shows a simple EventEmitter
instance with a single
listener. The eventEmitter.on()
method is used to register listeners, while
the eventEmitter.emit()
method is used to trigger the event.
const EventEmitter = require('events');
class MyEmitter extends EventEmitter {}
const myEmitter = new MyEmitter();
myEmitter.on('event', () => {
console.log('an event occurred!');
});
myEmitter.emit('event');
Passing arguments and this
to listeners#
The eventEmitter.emit()
method allows an arbitrary set of arguments to be
passed to the listener functions. It is important to keep in mind that when an
ordinary listener function is called by the EventEmitter
, the standard this
keyword is intentionally set to reference the EventEmitter
to which the
listener is attached.
const myEmitter = new MyEmitter();
myEmitter.on('event', function(a, b) {
console.log(a, b, this);
// Prints:
// a b MyEmitter {
// domain: null,
// _events: { event: [Function] },
// _eventsCount: 1,
// _maxListeners: undefined }
});
myEmitter.emit('event', 'a', 'b');
It is possible to use ES6 Arrow Functions as listeners, however, when doing so,
the this
keyword will no longer reference the EventEmitter
instance:
const myEmitter = new MyEmitter();
myEmitter.on('event', (a, b) => {
console.log(a, b, this);
// Prints: a b {}
});
myEmitter.emit('event', 'a', 'b');
Asynchronous vs. Synchronous#
The EventEmitter
calls all listeners synchronously in the order in which
they were registered. This is important to ensure the proper sequencing of
events and to avoid race conditions or logic errors. When appropriate,
listener functions can switch to an asynchronous mode of operation using
the setImmediate()
or process.nextTick()
methods:
const myEmitter = new MyEmitter();
myEmitter.on('event', (a, b) => {
setImmediate(() => {
console.log('this happens asynchronously');
});
});
myEmitter.emit('event', 'a', 'b');
Handling events only once#
When a listener is registered using the eventEmitter.on()
method, that
listener will be invoked every time the named event is emitted.
const myEmitter = new MyEmitter();
let m = 0;
myEmitter.on('event', () => {
console.log(++m);
});
myEmitter.emit('event');
// Prints: 1
myEmitter.emit('event');
// Prints: 2
Using the eventEmitter.once()
method, it is possible to register a listener
that is called at most once for a particular event. Once the event is emitted,
the listener is unregistered and then called.
const myEmitter = new MyEmitter();
let m = 0;
myEmitter.once('event', () => {
console.log(++m);
});
myEmitter.emit('event');
// Prints: 1
myEmitter.emit('event');
// Ignored
Error events#
When an error occurs within an EventEmitter
instance, the typical action is
for an 'error'
event to be emitted. These are treated as special cases
within Node.js.
If an EventEmitter
does not have at least one listener registered for the
'error'
event, and an 'error'
event is emitted, the error is thrown, a
stack trace is printed, and the Node.js process exits.
const myEmitter = new MyEmitter();
myEmitter.emit('error', new Error('whoops!'));
// Throws and crashes Node.js
To guard against crashing the Node.js process, a listener can be registered
on the process
object's uncaughtException
event or the domain
module
can be used. (Note, however, that the domain
module has been deprecated)
const myEmitter = new MyEmitter();
process.on('uncaughtException', (err) => {
console.error('whoops! there was an error');
});
myEmitter.emit('error', new Error('whoops!'));
// Prints: whoops! there was an error
As a best practice, listeners should always be added for the 'error'
events.
const myEmitter = new MyEmitter();
myEmitter.on('error', (err) => {
console.error('whoops! there was an error');
});
myEmitter.emit('error', new Error('whoops!'));
// Prints: whoops! there was an error
Class: EventEmitter#
The EventEmitter
class is defined and exposed by the events
module:
const EventEmitter = require('events');
All EventEmitters emit the event 'newListener'
when new listeners are
added and 'removeListener'
when existing listeners are removed.
Event: 'newListener'#
eventName
<string> | <symbol> The name of the event being listened forlistener
<Function> The event handler function
The EventEmitter
instance will emit its own 'newListener'
event before
a listener is added to its internal array of listeners.
Listeners registered for the 'newListener'
event will be passed the event
name and a reference to the listener being added.
The fact that the event is triggered before adding the listener has a subtle
but important side effect: any additional listeners registered to the same
name
within the 'newListener'
callback will be inserted before the
listener that is in the process of being added.
const myEmitter = new MyEmitter();
// Only do this once so we don't loop forever
myEmitter.once('newListener', (event, listener) => {
if (event === 'event') {
// Insert a new listener in front
myEmitter.on('event', () => {
console.log('B');
});
}
});
myEmitter.on('event', () => {
console.log('A');
});
myEmitter.emit('event');
// Prints:
// B
// A
Event: 'removeListener'#
eventName
<string> | <symbol> The event namelistener
<Function> The event handler function
The 'removeListener'
event is emitted after the listener
is removed.
EventEmitter.listenerCount(emitter, eventName)#
emitter.listenerCount()
instead.A class method that returns the number of listeners for the given eventName
registered on the given emitter
.
const myEmitter = new MyEmitter();
myEmitter.on('event', () => {});
myEmitter.on('event', () => {});
console.log(EventEmitter.listenerCount(myEmitter, 'event'));
// Prints: 2
EventEmitter.defaultMaxListeners#
By default, a maximum of 10
listeners can be registered for any single
event. This limit can be changed for individual EventEmitter
instances
using the emitter.setMaxListeners(n)
method. To change the default
for all EventEmitter
instances, the EventEmitter.defaultMaxListeners
property can be used.
Take caution when setting the EventEmitter.defaultMaxListeners
because the
change affects all EventEmitter
instances, including those created before
the change is made. However, calling emitter.setMaxListeners(n)
still has
precedence over EventEmitter.defaultMaxListeners
.
Note that this is not a hard limit. The EventEmitter
instance will allow
more listeners to be added but will output a trace warning to stderr indicating
that a "possible EventEmitter memory leak" has been detected. For any single
EventEmitter
, the emitter.getMaxListeners()
and emitter.setMaxListeners()
methods can be used to temporarily avoid this warning:
emitter.setMaxListeners(emitter.getMaxListeners() + 1);
emitter.once('event', () => {
// do stuff
emitter.setMaxListeners(Math.max(emitter.getMaxListeners() - 1, 0));
});
The --trace-warnings
command line flag can be used to display the
stack trace for such warnings.
The emitted warning can be inspected with process.on('warning')
and will
have the additional emitter
, type
and count
properties, referring to
the event emitter instance, the event’s name and the number of attached
listeners, respectively.
emitter.addListener(eventName, listener)#
Alias for emitter.on(eventName, listener)
.
emitter.emit(eventName[, ...args])#
Synchronously calls each of the listeners registered for the event named
eventName
, in the order they were registered, passing the supplied arguments
to each.
Returns true
if the event had listeners, false
otherwise.
emitter.eventNames()#
Returns an array listing the events for which the emitter has registered listeners. The values in the array will be strings or Symbols.
const EventEmitter = require('events');
const myEE = new EventEmitter();
myEE.on('foo', () => {});
myEE.on('bar', () => {});
const sym = Symbol('symbol');
myEE.on(sym, () => {});
console.log(myEE.eventNames());
// Prints: [ 'foo', 'bar', Symbol(symbol) ]
emitter.getMaxListeners()#
Returns the current max listener value for the EventEmitter
which is either
set by emitter.setMaxListeners(n)
or defaults to
EventEmitter.defaultMaxListeners
.
emitter.listenerCount(eventName)#
Returns the number of listeners listening to the event named eventName
.
emitter.listeners(eventName)#
Returns a copy of the array of listeners for the event named eventName
.
server.on('connection', (stream) => {
console.log('someone connected!');
});
console.log(util.inspect(server.listeners('connection')));
// Prints: [ [Function] ]
emitter.on(eventName, listener)#
eventName
<string> | <symbol> The name of the event.listener
<Function> The callback function
Adds the listener
function to the end of the listeners array for the
event named eventName
. No checks are made to see if the listener
has
already been added. Multiple calls passing the same combination of eventName
and listener
will result in the listener
being added, and called, multiple
times.
server.on('connection', (stream) => {
console.log('someone connected!');
});
Returns a reference to the EventEmitter
, so that calls can be chained.
By default, event listeners are invoked in the order they are added. The
emitter.prependListener()
method can be used as an alternative to add the
event listener to the beginning of the listeners array.
const myEE = new EventEmitter();
myEE.on('foo', () => console.log('a'));
myEE.prependListener('foo', () => console.log('b'));
myEE.emit('foo');
// Prints:
// b
// a
emitter.once(eventName, listener)#
eventName
<string> | <symbol> The name of the event.listener
<Function> The callback function
Adds a one-time listener
function for the event named eventName
. The
next time eventName
is triggered, this listener is removed and then invoked.
server.once('connection', (stream) => {
console.log('Ah, we have our first user!');
});
Returns a reference to the EventEmitter
, so that calls can be chained.
By default, event listeners are invoked in the order they are added. The
emitter.prependOnceListener()
method can be used as an alternative to add the
event listener to the beginning of the listeners array.
const myEE = new EventEmitter();
myEE.once('foo', () => console.log('a'));
myEE.prependOnceListener('foo', () => console.log('b'));
myEE.emit('foo');
// Prints:
// b
// a
emitter.prependListener(eventName, listener)#
eventName
<string> | <symbol> The name of the event.listener
<Function> The callback function
Adds the listener
function to the beginning of the listeners array for the
event named eventName
. No checks are made to see if the listener
has
already been added. Multiple calls passing the same combination of eventName
and listener
will result in the listener
being added, and called, multiple
times.
server.prependListener('connection', (stream) => {
console.log('someone connected!');
});
Returns a reference to the EventEmitter
, so that calls can be chained.
emitter.prependOnceListener(eventName, listener)#
eventName
<string> | <symbol> The name of the event.listener
<Function> The callback function
Adds a one-time listener
function for the event named eventName
to the
beginning of the listeners array. The next time eventName
is triggered, this
listener is removed, and then invoked.
server.prependOnceListener('connection', (stream) => {
console.log('Ah, we have our first user!');
});
Returns a reference to the EventEmitter
, so that calls can be chained.
emitter.removeAllListeners([eventName])#
Removes all listeners, or those of the specified eventName
.
Note that it is bad practice to remove listeners added elsewhere in the code,
particularly when the EventEmitter
instance was created by some other
component or module (e.g. sockets or file streams).
Returns a reference to the EventEmitter
, so that calls can be chained.
emitter.removeListener(eventName, listener)#
Removes the specified listener
from the listener array for the event named
eventName
.
const callback = (stream) => {
console.log('someone connected!');
};
server.on('connection', callback);
// ...
server.removeListener('connection', callback);
removeListener
will remove, at most, one instance of a listener from the
listener array. If any single listener has been added multiple times to the
listener array for the specified eventName
, then removeListener
must be
called multiple times to remove each instance.
Note that once an event has been emitted, all listeners attached to it at the
time of emitting will be called in order. This implies that any removeListener()
or removeAllListeners()
calls after emitting and before the last listener
finishes execution will not remove them from emit()
in progress. Subsequent
events will behave as expected.
const myEmitter = new MyEmitter();
const callbackA = () => {
console.log('A');
myEmitter.removeListener('event', callbackB);
};
const callbackB = () => {
console.log('B');
};
myEmitter.on('event', callbackA);
myEmitter.on('event', callbackB);
// callbackA removes listener callbackB but it will still be called.
// Internal listener array at time of emit [callbackA, callbackB]
myEmitter.emit('event');
// Prints:
// A
// B
// callbackB is now removed.
// Internal listener array [callbackA]
myEmitter.emit('event');
// Prints:
// A
Because listeners are managed using an internal array, calling this will
change the position indices of any listener registered after the listener
being removed. This will not impact the order in which listeners are called,
but it means that any copies of the listener array as returned by
the emitter.listeners()
method will need to be recreated.
Returns a reference to the EventEmitter
, so that calls can be chained.
emitter.setMaxListeners(n)#
By default EventEmitters will print a warning if more than 10
listeners are
added for a particular event. This is a useful default that helps finding
memory leaks. Obviously, not all events should be limited to just 10 listeners.
The emitter.setMaxListeners()
method allows the limit to be modified for this
specific EventEmitter
instance. The value can be set to Infinity
(or 0
)
to indicate an unlimited number of listeners.
Returns a reference to the EventEmitter
, so that calls can be chained.
File System#
File I/O is provided by simple wrappers around standard POSIX functions. To
use this module do require('fs')
. All the methods have asynchronous and
synchronous forms.
The asynchronous form always takes a completion callback as its last argument.
The arguments passed to the completion callback depend on the method, but the
first argument is always reserved for an exception. If the operation was
completed successfully, then the first argument will be null
or undefined
.
When using the synchronous form any exceptions are immediately thrown. You can use try/catch to handle exceptions or allow them to bubble up.
Here is an example of the asynchronous version:
const fs = require('fs');
fs.unlink('/tmp/hello', (err) => {
if (err) throw err;
console.log('successfully deleted /tmp/hello');
});
Here is the synchronous version:
const fs = require('fs');
fs.unlinkSync('/tmp/hello');
console.log('successfully deleted /tmp/hello');
With the asynchronous methods there is no guaranteed ordering. So the following is prone to error:
fs.rename('/tmp/hello', '/tmp/world', (err) => {
if (err) throw err;
console.log('renamed complete');
});
fs.stat('/tmp/world', (err, stats) => {
if (err) throw err;
console.log(`stats: ${JSON.stringify(stats)}`);
});
It could be that fs.stat
is executed before fs.rename
.
The correct way to do this is to chain the callbacks.
fs.rename('/tmp/hello', '/tmp/world', (err) => {
if (err) throw err;
fs.stat('/tmp/world', (err, stats) => {
if (err) throw err;
console.log(`stats: ${JSON.stringify(stats)}`);
});
});
In busy processes, the programmer is strongly encouraged to use the asynchronous versions of these calls. The synchronous versions will block the entire process until they complete--halting all connections.
The relative path to a filename can be used. Remember, however, that this path
will be relative to process.cwd()
.
Most fs functions let you omit the callback argument. If you do, a default
callback is used that rethrows errors. To get a trace to the original call
site, set the NODE_DEBUG
environment variable:
$ cat script.js
function bad() {
require('fs').readFile('/');
}
bad();
$ env NODE_DEBUG=fs node script.js
fs.js:88
throw backtrace;
^
Error: EISDIR: illegal operation on a directory, read
<stack trace.>
Buffer API#
fs
functions support passing and receiving paths as both strings
and Buffers. The latter is intended to make it possible to work with
filesystems that allow for non-UTF-8 filenames. For most typical
uses, working with paths as Buffers will be unnecessary, as the string
API converts to and from UTF-8 automatically.
Note that on certain file systems (such as NTFS and HFS+) filenames
will always be encoded as UTF-8. On such file systems, passing
non-UTF-8 encoded Buffers to fs
functions will not work as expected.
Class: fs.FSWatcher#
Objects returned from fs.watch()
are of this type.
The listener
callback provided to fs.watch()
receives the returned FSWatcher's
change
events.
The object itself emits these events:
Event: 'change'#
eventType
<string> The type of fs changefilename
<string> | <Buffer> The filename that changed (if relevant/available)
Emitted when something changes in a watched directory or file.
See more details in fs.watch()
.
The filename
argument may not be provided depending on operating system
support. If filename
is provided, it will be provided as a Buffer
if
fs.watch()
is called with its encoding
option set to 'buffer'
, otherwise
filename
will be a string.
// Example when handled through fs.watch listener
fs.watch('./tmp', {encoding: 'buffer'}, (eventType, filename) => {
if (filename)
console.log(filename);
// Prints: <Buffer ...>
});
Event: 'error'#
error
<Error>
Emitted when an error occurs.
watcher.close()#
Stop watching for changes on the given fs.FSWatcher
.
Class: fs.ReadStream#
ReadStream
is a Readable Stream.
Event: 'open'#
fd
<Integer> Integer file descriptor used by the ReadStream.
Emitted when the ReadStream's file is opened.
Event: 'close'#
fd
<integer> Integer file descriptor used by the ReadStream.
Emitted when the ReadStream
's underlying file descriptor has been closed.
readStream.bytesRead#
The number of bytes read so far.
readStream.path#
The path to the file the stream is reading from as specified in the first
argument to fs.createReadStream()
. If path
is passed as a string, then
readStream.path
will be a string. If path
is passed as a Buffer
, then
readStream.path
will be a Buffer
.
Class: fs.Stats#
Objects returned from fs.stat()
, fs.lstat()
and fs.fstat()
and their
synchronous counterparts are of this type.
stats.isFile()
stats.isDirectory()
stats.isBlockDevice()
stats.isCharacterDevice()
stats.isSymbolicLink()
(only valid withfs.lstat()
)stats.isFIFO()
stats.isSocket()
For a regular file util.inspect(stats)
would return a string very
similar to this:
Stats {
dev: 2114,
ino: 48064969,
mode: 33188,
nlink: 1,
uid: 85,
gid: 100,
rdev: 0,
size: 527,
blksize: 4096,
blocks: 8,
atime: Mon, 10 Oct 2011 23:24:11 GMT,
mtime: Mon, 10 Oct 2011 23:24:11 GMT,
ctime: Mon, 10 Oct 2011 23:24:11 GMT,
birthtime: Mon, 10 Oct 2011 23:24:11 GMT }
Please note that atime
, mtime
, birthtime
, and ctime
are
instances of Date
object and to compare the values of
these objects you should use appropriate methods. For most general
uses getTime()
will return the number of
milliseconds elapsed since 1 January 1970 00:00:00 UTC and this
integer should be sufficient for any comparison, however there are
additional methods which can be used for displaying fuzzy information.
More details can be found in the MDN JavaScript Reference
page.
Stat Time Values#
The times in the stat object have the following semantics:
atime
"Access Time" - Time when file data last accessed. Changed by the mknod(2), utimes(2), and read(2) system calls.mtime
"Modified Time" - Time when file data last modified. Changed by the mknod(2), utimes(2), and write(2) system calls.ctime
"Change Time" - Time when file status was last changed (inode data modification). Changed by the chmod(2), chown(2), link(2), mknod(2), rename(2), unlink(2), utimes(2), read(2), and write(2) system calls.birthtime
"Birth Time" - Time of file creation. Set once when the file is created. On filesystems where birthtime is not available, this field may instead hold either thectime
or1970-01-01T00:00Z
(ie, unix epoch timestamp0
). Note that this value may be greater thanatime
ormtime
in this case. On Darwin and other FreeBSD variants, also set if theatime
is explicitly set to an earlier value than the currentbirthtime
using the utimes(2) system call.
Prior to Node v0.12, the ctime
held the birthtime
on Windows
systems. Note that as of v0.12, ctime
is not "creation time", and
on Unix systems, it never was.
Class: fs.WriteStream#
WriteStream
is a Writable Stream.
Event: 'open'#
fd
<Integer> Integer file descriptor used by the WriteStream.
Emitted when the WriteStream's file is opened.
Event: 'close'#
fd
<integer> Integer file descriptor used by the WriteStream.
Emitted when the WriteStream
's underlying file descriptor has been closed.
writeStream.bytesWritten#
The number of bytes written so far. Does not include data that is still queued for writing.
writeStream.path#
The path to the file the stream is writing to as specified in the first
argument to fs.createWriteStream()
. If path
is passed as a string, then
writeStream.path
will be a string. If path
is passed as a Buffer
, then
writeStream.path
will be a Buffer
.
fs.access(path[, mode], callback)#
path
<string> | <Buffer>mode
<integer>callback
<Function>err
<Error>
Tests a user's permissions for the file or directory specified by path
.
The mode
argument is an optional integer that specifies the accessibility
checks to be performed. The following constants define the possible values of
mode
. It is possible to create a mask consisting of the bitwise OR of two or
more values.
fs.constants.F_OK
-path
is visible to the calling process. This is useful for determining if a file exists, but says nothing aboutrwx
permissions. Default if nomode
is specified.fs.constants.R_OK
-path
can be read by the calling process.fs.constants.W_OK
-path
can be written by the calling process.fs.constants.X_OK
-path
can be executed by the calling process. This has no effect on Windows (will behave likefs.constants.F_OK
).
The final argument, callback
, is a callback function that is invoked with
a possible error argument. If any of the accessibility checks fail, the error
argument will be populated. The following example checks if the file
/etc/passwd
can be read and written by the current process.
fs.access('/etc/passwd', fs.constants.R_OK | fs.constants.W_OK, (err) => {
console.log(err ? 'no access!' : 'can read/write');
});
Using fs.access()
to check for the accessibility of a file before calling
fs.open()
, fs.readFile()
or fs.writeFile()
is not recommended. Doing
so introduces a race condition, since other processes may change the file's
state between the two calls. Instead, user code should open/read/write the
file directly and handle the error raised if the file is not accessible.
For example:
write (NOT RECOMMENDED)
fs.access('myfile', (err) => {
if (!err) {
console.error('myfile already exists');
return;
}
fs.open('myfile', 'wx', (err, fd) => {
if (err) throw err;
writeMyData(fd);
});
});
write (RECOMMENDED)
fs.open('myfile', 'wx', (err, fd) => {
if (err) {
if (err.code === 'EEXIST') {
console.error('myfile already exists');
return;
}
throw err;
}
writeMyData(fd);
});
read (NOT RECOMMENDED)
fs.access('myfile', (err) => {
if (err) {
if (err.code === 'ENOENT') {
console.error('myfile does not exist');
return;
}
throw err;
}
fs.open('myfile', 'r', (err, fd) => {
if (err) throw err;
readMyData(fd);
});
});
read (RECOMMENDED)
fs.open('myfile', 'r', (err, fd) => {
if (err) {
if (err.code === 'ENOENT') {
console.error('myfile does not exist');
return;
}
throw err;
}
readMyData(fd);
});
The "not recommended" examples above check for accessibility and then use the file; the "recommended" examples are better because they use the file directly and handle the error, if any.
In general, check for the accessibility of a file only if the file won’t be used directly, for example when its accessibility is a signal from another process.
fs.accessSync(path[, mode])#
Synchronous version of fs.access()
. This throws if any accessibility
checks fail, and does nothing otherwise.
fs.appendFile(file, data[, options], callback)#
file
<string> | <Buffer> | <number> filename or file descriptordata
<string> | <Buffer>options
<Object> | <string>callback
<Function>err
<Error>
Asynchronously append data to a file, creating the file if it does not yet exist.
data
can be a string or a buffer.
Example:
fs.appendFile('message.txt', 'data to append', (err) => {
if (err) throw err;
console.log('The "data to append" was appended to file!');
});
If options
is a string, then it specifies the encoding. Example:
fs.appendFile('message.txt', 'data to append', 'utf8', callback);
Any specified file descriptor has to have been opened for appending.
Note: If a file descriptor is specified as the file
, it will not be closed
automatically.
fs.appendFileSync(file, data[, options])#
file
<string> | <Buffer> | <number> filename or file descriptordata
<string> | <Buffer>options
<Object> | <string>
The synchronous version of fs.appendFile()
. Returns undefined
.
fs.chmod(path, mode, callback)#
path
<string> | <Buffer>mode
<integer>callback
<Function>err
<Error>
Asynchronously changes the permissions of a file. No arguments other than a possible exception are given to the completion callback.
See also: chmod(2)
fs.chmodSync(path, mode)#
Synchronously changes the permissions of a file. Returns undefined
.
This is the synchronous version of fs.chmod()
.
See also: chmod(2)
fs.chown(path, uid, gid, callback)#
Asynchronously changes owner and group of a file. No arguments other than a possible exception are given to the completion callback.
See also: chown(2)
fs.chownSync(path, uid, gid)#
Synchronously changes owner and group of a file. Returns undefined
.
This is the synchronous version of fs.chown()
.
See also: chown(2)
fs.close(fd, callback)#
fd
<integer>callback
<Function>err
<Error>
Asynchronous close(2). No arguments other than a possible exception are given to the completion callback.
fs.closeSync(fd)#
fd
<integer>
Synchronous close(2). Returns undefined
.
fs.constants#
Returns an object containing commonly used constants for file system operations. The specific constants currently defined are described in FS Constants.
fs.createReadStream(path[, options])#
Returns a new ReadStream
object. (See Readable Stream).
Be aware that, unlike the default value set for highWaterMark
on a
readable stream (16 kb), the stream returned by this method has a
default value of 64 kb for the same parameter.
options
is an object or string with the following defaults:
const defaults = {
flags: 'r',
encoding: null,
fd: null,
mode: 0o666,
autoClose: true,
highWaterMark: 64 * 1024
};
options
can include start
and end
values to read a range of bytes from
the file instead of the entire file. Both start
and end
are inclusive and
start counting at 0. If fd
is specified and start
is omitted or undefined
,
fs.createReadStream()
reads sequentially from the current file position.
The encoding
can be any one of those accepted by Buffer
.
If fd
is specified, ReadStream
will ignore the path
argument and will use
the specified file descriptor. This means that no 'open'
event will be
emitted. Note that fd
should be blocking; non-blocking fd
s should be passed
to net.Socket
.
If autoClose
is false, then the file descriptor won't be closed, even if
there's an error. It is your responsibility to close it and make sure
there's no file descriptor leak. If autoClose
is set to true (default
behavior), on error
or end
the file descriptor will be closed
automatically.
mode
sets the file mode (permission and sticky bits), but only if the
file was created.
An example to read the last 10 bytes of a file which is 100 bytes long:
fs.createReadStream('sample.txt', {start: 90, end: 99});
If options
is a string, then it specifies the encoding.
fs.createWriteStream(path[, options])#
Returns a new WriteStream
object. (See Writable Stream).
options
is an object or string with the following defaults:
const defaults = {
flags: 'w',
defaultEncoding: 'utf8',
fd: null,
mode: 0o666,
autoClose: true
};
options
may also include a start
option to allow writing data at
some position past the beginning of the file. Modifying a file rather
than replacing it may require a flags
mode of r+
rather than the
default mode w
. The defaultEncoding
can be any one of those accepted by
Buffer
.
If autoClose
is set to true (default behavior) on error
or end
the file descriptor will be closed automatically. If autoClose
is false,
then the file descriptor won't be closed, even if there's an error.
It is your responsibility to close it and make sure
there's no file descriptor leak.
Like ReadStream
, if fd
is specified, WriteStream
will ignore the
path
argument and will use the specified file descriptor. This means that no
'open'
event will be emitted. Note that fd
should be blocking; non-blocking
fd
s should be passed to net.Socket
.
If options
is a string, then it specifies the encoding.
fs.exists(path, callback)#
path
<string> | <Buffer>callback
<Function>exists
<Boolean>
Test whether or not the given path exists by checking with the file system.
Then call the callback
argument with either true or false. Example:
fs.exists('/etc/passwd', (exists) => {
console.log(exists ? 'it\'s there' : 'no passwd!');
});
Note that the parameter to this callback is not consistent with other
Node.js callbacks. Normally, the first parameter to a Node.js callback is
an err
parameter, optionally followed by other parameters. The
fs.exists()
callback has only one boolean parameter. This is one reason
fs.access()
is recommended instead of fs.exists()
.
Using fs.exists()
to check for the existence of a file before calling
fs.open()
, fs.readFile()
or fs.writeFile()
is not recommended. Doing
so introduces a race condition, since other processes may change the file's
state between the two calls. Instead, user code should open/read/write the
file directly and handle the error raised if the file does not exist.
For example:
write (NOT RECOMMENDED)
fs.exists('myfile', (exists) => {
if (exists) {
console.error('myfile already exists');
} else {
fs.open('myfile', 'wx', (err, fd) => {
if (err) throw err;
writeMyData(fd);
});
}
});
write (RECOMMENDED)
fs.open('myfile', 'wx', (err, fd) => {
if (err) {
if (err.code === 'EEXIST') {
console.error('myfile already exists');
return;
}
throw err;
}
writeMyData(fd);
});
read (NOT RECOMMENDED)
fs.exists('myfile', (exists) => {
if (exists) {
fs.open('myfile', 'r', (err, fd) => {
readMyData(fd);
});
} else {
console.error('myfile does not exist');
}
});
read (RECOMMENDED)
fs.open('myfile', 'r', (err, fd) => {
if (err) {
if (err.code === 'ENOENT') {
console.error('myfile does not exist');
return;
}
throw err;
}
readMyData(fd);
});
The "not recommended" examples above check for existence and then use the file; the "recommended" examples are better because they use the file directly and handle the error, if any.
In general, check for the existence of a file only if the file won’t be used directly, for example when its existence is a signal from another process.
fs.existsSync(path)#
Synchronous version of fs.exists()
.
Returns true
if the path exists, false
otherwise.
Note that fs.exists()
is deprecated, but fs.existsSync()
is not.
(The callback
parameter to fs.exists()
accepts parameters that are
inconsistent with other Node.js callbacks. fs.existsSync()
does not use
a callback.)
fs.fchmod(fd, mode, callback)#
fd
<integer>mode
<integer>callback
<Function>err
<Error>
Asynchronous fchmod(2). No arguments other than a possible exception are given to the completion callback.
fs.fchmodSync(fd, mode)#
Synchronous fchmod(2). Returns undefined
.
fs.fchown(fd, uid, gid, callback)#
fd
<integer>uid
<integer>gid
<integer>callback
<Function>err
<Error>
Asynchronous fchown(2). No arguments other than a possible exception are given to the completion callback.
fs.fchownSync(fd, uid, gid)#
Synchronous fchown(2). Returns undefined
.
fs.fdatasync(fd, callback)#
fd
<integer>callback
<Function>err
<Error>
Asynchronous fdatasync(2). No arguments other than a possible exception are given to the completion callback.
fs.fdatasyncSync(fd)#
fd
<integer>
Synchronous fdatasync(2). Returns undefined
.
fs.fstat(fd, callback)#
fd
<integer>callback
<Function>err
<Error>stats
<fs.Stats>
Asynchronous fstat(2). The callback gets two arguments (err, stats)
where
stats
is an fs.Stats
object. fstat()
is identical to stat()
,
except that the file to be stat-ed is specified by the file descriptor fd
.
fs.fstatSync(fd)#
fd
<integer>
Synchronous fstat(2). Returns an instance of fs.Stats
.
fs.fsync(fd, callback)#
fd
<integer>callback
<Function>err
<Error>
Asynchronous fsync(2). No arguments other than a possible exception are given to the completion callback.
fs.fsyncSync(fd)#
fd
<integer>
Synchronous fsync(2). Returns undefined
.
fs.ftruncate(fd, len, callback)#
fd
<integer>len
<integer> default =0
callback
<Function>err
<Error>
Asynchronous ftruncate(2). No arguments other than a possible exception are given to the completion callback.
If the file referred to by the file descriptor was larger than len
bytes, only
the first len
bytes will be retained in the file.
For example, the following program retains only the first four bytes of the file
console.log(fs.readFileSync('temp.txt', 'utf8'));
// Prints: Node.js
// get the file descriptor of the file to be truncated
const fd = fs.openSync('temp.txt', 'r+');
// truncate the file to first four bytes
fs.ftruncate(fd, 4, (err) => {
assert.ifError(err);
console.log(fs.readFileSync('temp.txt', 'utf8'));
});
// Prints: Node
If the file previously was shorter than len
bytes, it is extended, and the
extended part is filled with null bytes ('\0'). For example,
console.log(fs.readFileSync('temp.txt', 'utf8'));
// Prints: Node.js
// get the file descriptor of the file to be truncated
const fd = fs.openSync('temp.txt', 'r+');
// truncate the file to 10 bytes, whereas the actual size is 7 bytes
fs.ftruncate(fd, 10, (err) => {
assert.ifError(err);
console.log(fs.readFileSync('temp.txt'));
});
// Prints: <Buffer 4e 6f 64 65 2e 6a 73 00 00 00>
// ('Node.js\0\0\0' in UTF8)
The last three bytes are null bytes ('\0'), to compensate the over-truncation.
fs.ftruncateSync(fd, len)#
Synchronous ftruncate(2). Returns undefined
.
fs.futimes(fd, atime, mtime, callback)#
fd
<integer>atime
<integer>mtime
<integer>callback
<Function>err
<Error>
Change the file timestamps of a file referenced by the supplied file descriptor.
Note: This function does not work on AIX versions before 7.1, it will return
the error UV_ENOSYS
.
fs.futimesSync(fd, atime, mtime)#
Synchronous version of fs.futimes()
. Returns undefined
.
fs.lchmod(path, mode, callback)#
path
<string> | <Buffer>mode
<integer>callback
<Function>err
<Error>
Asynchronous lchmod(2). No arguments other than a possible exception are given to the completion callback.
Only available on macOS.
fs.lchmodSync(path, mode)#
Synchronous lchmod(2). Returns undefined
.
fs.lchown(path, uid, gid, callback)#
Asynchronous lchown(2). No arguments other than a possible exception are given to the completion callback.
fs.lchownSync(path, uid, gid)#
Synchronous lchown(2). Returns undefined
.
fs.link(existingPath, newPath, callback)#
Asynchronous link(2). No arguments other than a possible exception are given to the completion callback.
fs.linkSync(existingPath, newPath)#
Synchronous link(2). Returns undefined
.
fs.lstat(path, callback)#
path
<string> | <Buffer>callback
<Function>err
<Error>stats
<fs.Stats>
Asynchronous lstat(2). The callback gets two arguments (err, stats)
where
stats
is a fs.Stats
object. lstat()
is identical to stat()
,
except that if path
is a symbolic link, then the link itself is stat-ed,
not the file that it refers to.
fs.lstatSync(path)#
Synchronous lstat(2). Returns an instance of fs.Stats
.
fs.mkdir(path[, mode], callback)#
path
<string> | <Buffer>mode
<integer>callback
<Function>err
<Error>
Asynchronously creates a directory. No arguments other than a possible exception
are given to the completion callback. mode
defaults to 0o777
.
See also: mkdir(2)
fs.mkdirSync(path[, mode])#
Synchronously creates a directory. Returns undefined
.
This is the synchronous version of fs.mkdir()
.
See also: mkdir(2)
fs.mkdtemp(prefix[, options], callback)#
prefix
<string>options
<string> | <Object>encoding
<string> default ='utf8'
callback
<Function>
Creates a unique temporary directory.
Generates six random characters to be appended behind a required
prefix
to create a unique temporary directory.
The created folder path is passed as a string to the callback's second parameter.
The optional options
argument can be a string specifying an encoding, or an
object with an encoding
property specifying the character encoding to use.
Example:
fs.mkdtemp(path.join(os.tmpdir(), 'foo-'), (err, folder) => {
if (err) throw err;
console.log(folder);
// Prints: /tmp/foo-itXde2 or C:\Users\...\AppData\Local\Temp\foo-itXde2
});
Note: The fs.mkdtemp()
method will append the six randomly selected
characters directly to the prefix
string. For instance, given a directory
/tmp
, if the intention is to create a temporary directory within /tmp
,
the prefix
must end with a trailing platform-specific path separator
(require('path').sep
).
// The parent directory for the new temporary directory
const tmpDir = os.tmpdir();
// This method is *INCORRECT*:
fs.mkdtemp(tmpDir, (err, folder) => {
if (err) throw err;
console.log(folder);
// Will print something similar to `/tmpabc123`.
// Note that a new temporary directory is created
// at the file system root rather than *within*
// the /tmp directory.
});
// This method is *CORRECT*:
const { sep } = require('path');
fs.mkdtemp(`${tmpDir}${sep}`, (err, folder) => {
if (err) throw err;
console.log(folder);
// Will print something similar to `/tmp/abc123`.
// A new temporary directory is created within
// the /tmp directory.
});
fs.mkdtempSync(prefix[, options])#
The synchronous version of fs.mkdtemp()
. Returns the created
folder path.
The optional options
argument can be a string specifying an encoding, or an
object with an encoding
property specifying the character encoding to use.
fs.open(path, flags[, mode], callback)#
Asynchronous file open. See open(2). flags
can be:
'r'
- Open file for reading. An exception occurs if the file does not exist.'r+'
- Open file for reading and writing. An exception occurs if the file does not exist.'rs+'
- Open file for reading and writing in synchronous mode. Instructs the operating system to bypass the local file system cache.This is primarily useful for opening files on NFS mounts as it allows you to skip the potentially stale local cache. It has a very real impact on I/O performance so don't use this flag unless you need it.
Note that this doesn't turn
fs.open()
into a synchronous blocking call. If that's what you want then you should be usingfs.openSync()
'w'
- Open file for writing. The file is created (if it does not exist) or truncated (if it exists).'wx'
- Like'w'
but fails ifpath
exists.'w+'
- Open file for reading and writing. The file is created (if it does not exist) or truncated (if it exists).'wx+'
- Like'w+'
but fails ifpath
exists.'a'
- Open file for appending. The file is created if it does not exist.'ax'
- Like'a'
but fails ifpath
exists.'a+'
- Open file for reading and appending. The file is created if it does not exist.'ax+'
- Like'a+'
but fails ifpath
exists.
mode
sets the file mode (permission and sticky bits), but only if the file was
created. It defaults to 0o666
(readable and writable).
The callback gets two arguments (err, fd)
.
The exclusive flag 'x'
(O_EXCL
flag in open(2)) ensures that path
is newly
created. On POSIX systems, path
is considered to exist even if it is a symlink
to a non-existent file. The exclusive flag may or may not work with network file
systems.
flags
can also be a number as documented by open(2); commonly used constants
are available from fs.constants
. On Windows, flags are translated to
their equivalent ones where applicable, e.g. O_WRONLY
to FILE_GENERIC_WRITE
,
or O_EXCL|O_CREAT
to CREATE_NEW
, as accepted by CreateFileW.
On Linux, positional writes don't work when the file is opened in append mode. The kernel ignores the position argument and always appends the data to the end of the file.
Note: The behavior of fs.open()
is platform-specific for some flags. As such,
opening a directory on macOS and Linux with the 'a+'
flag - see example
below - will return an error. In contrast, on Windows and FreeBSD, a file
descriptor will be returned.
// macOS and Linux
fs.open('<directory>', 'a+', (err, fd) => {
// => [Error: EISDIR: illegal operation on a directory, open <directory>]
});
// Windows and FreeBSD
fs.open('<directory>', 'a+', (err, fd) => {
// => null, <fd>
});
Some characters (< > : " / \ | ? *
) are reserved under Windows as documented
by Naming Files, Paths, and Namespaces. Under NTFS, if the filename contains
a colon, Node.js will open a file system stream, as described by
this MSDN page.
Functions based on fs.open()
exhibit this behavior as well. eg.
fs.writeFile()
, fs.readFile()
, etc.
fs.openSync(path, flags[, mode])#
Synchronous version of fs.open()
. Returns an integer representing the file
descriptor.
fs.read(fd, buffer, offset, length, position, callback)#
fd
<integer>buffer
<string> | <Buffer>offset
<integer>length
<integer>position
<integer>callback
<Function>
Read data from the file specified by fd
.
buffer
is the buffer that the data will be written to.
offset
is the offset in the buffer to start writing at.
length
is an integer specifying the number of bytes to read.
position
is an argument specifying where to begin reading from in the file.
If position
is null
, data will be read from the current file position,
and the file position will be updated.
If position
is an integer, the file position will remain unchanged.
The callback is given the three arguments, (err, bytesRead, buffer)
.
fs.readdir(path[, options], callback)#
path
<string> | <Buffer>options
<string> | <Object>encoding
<string> default ='utf8'
callback
<Function>err
<Error>files
<string[]> | <Buffer[]>
Asynchronous readdir(3). Reads the contents of a directory.
The callback gets two arguments (err, files)
where files
is an array of
the names of the files in the directory excluding '.'
and '..'
.
The optional options
argument can be a string specifying an encoding, or an
object with an encoding
property specifying the character encoding to use for
the filenames passed to the callback. If the encoding
is set to 'buffer'
,
the filenames returned will be passed as Buffer
objects.
fs.readdirSync(path[, options])#
Synchronous readdir(3). Returns an array of filenames excluding '.'
and
'..'
.
The optional options
argument can be a string specifying an encoding, or an
object with an encoding
property specifying the character encoding to use for
the filenames passed to the callback. If the encoding
is set to 'buffer'
,
the filenames returned will be passed as Buffer
objects.
fs.readFile(file[, options], callback)#
file
<string> | <Buffer> | <integer> filename or file descriptoroptions
<Object> | <string>callback
<Function>
Asynchronously reads the entire contents of a file. Example:
fs.readFile('/etc/passwd', (err, data) => {
if (err) throw err;
console.log(data);
});
The callback is passed two arguments (err, data)
, where data
is the
contents of the file.
If no encoding is specified, then the raw buffer is returned.
If options
is a string, then it specifies the encoding. Example:
fs.readFile('/etc/passwd', 'utf8', callback);
Note: When the path is a directory, the behavior of
fs.readFile()
and [fs.readFileSync()
][] is platform-specific. On macOS,
Linux, and Windows, an error will be returned. On FreeBSD, a representation
of the directory's contents will be returned.
// macOS, Linux and Windows
fs.readFile('<directory>', (err, data) => {
// => [Error: EISDIR: illegal operation on a directory, read <directory>]
});
// FreeBSD
fs.readFile('<directory>', (err, data) => {
// => null, <data>
});
Any specified file descriptor has to support reading.
Note: If a file descriptor is specified as the path
, it will not be closed
automatically.
fs.readFileSync(file[, options])#
Synchronous version of fs.readFile
. Returns the contents of the file
.
If the encoding
option is specified then this function returns a
string. Otherwise it returns a buffer.
Note: Similar to [fs.readFile()
][], when the path is a directory, the
behavior of fs.readFileSync()
is platform-specific.
// macOS, Linux and Windows
fs.readFileSync('<directory>');
// => [Error: EISDIR: illegal operation on a directory, read <directory>]
// FreeBSD
fs.readFileSync('<directory>'); // => null, <data>
fs.readlink(path[, options], callback)#
path
<string> | <Buffer>options
<string> | <Object>encoding
<string> default ='utf8'
callback
<Function>
Asynchronous readlink(2). The callback gets two arguments (err,
linkString)
.
The optional options
argument can be a string specifying an encoding, or an
object with an encoding
property specifying the character encoding to use for
the link path passed to the callback. If the encoding
is set to 'buffer'
,
the link path returned will be passed as a Buffer
object.
fs.readlinkSync(path[, options])#
Synchronous readlink(2). Returns the symbolic link's string value.
The optional options
argument can be a string specifying an encoding, or an
object with an encoding
property specifying the character encoding to use for
the link path passed to the callback. If the encoding
is set to 'buffer'
,
the link path returned will be passed as a Buffer
object.
fs.readSync(fd, buffer, offset, length, position)#
Synchronous version of fs.read()
. Returns the number of bytesRead
.
fs.realpath(path[, options], callback)#
path
<string> | <Buffer>options
<string> | <Object>encoding
<string> default ='utf8'
callback
<Function>
Asynchronous realpath(3). The callback
gets two arguments (err,
resolvedPath)
. May use process.cwd
to resolve relative paths.
Only paths that can be converted to UTF8 strings are supported.
The optional options
argument can be a string specifying an encoding, or an
object with an encoding
property specifying the character encoding to use for
the path passed to the callback. If the encoding
is set to 'buffer'
,
the path returned will be passed as a Buffer
object.
fs.realpathSync(path[, options])#
Synchronous realpath(3). Returns the resolved path.
Only paths that can be converted to UTF8 strings are supported.
The optional options
argument can be a string specifying an encoding, or an
object with an encoding
property specifying the character encoding to use for
the returned value. If the encoding
is set to 'buffer'
, the path returned
will be passed as a Buffer
object.
fs.rename(oldPath, newPath, callback)#
Asynchronous rename(2). No arguments other than a possible exception are given to the completion callback.
fs.renameSync(oldPath, newPath)#
Synchronous rename(2). Returns undefined
.
fs.rmdir(path, callback)#
path
<string> | <Buffer>callback
<Function>err
<Error>
Asynchronous rmdir(2). No arguments other than a possible exception are given to the completion callback.
Note: Using fs.rmdir()
on a file (not a directory) results in an ENOENT
error on Windows and an ENOTDIR
error on POSIX.
fs.rmdirSync(path)#
Synchronous rmdir(2). Returns undefined
.
Note: Using fs.rmdirSync()
on a file (not a directory) results in an ENOENT
error on Windows and an ENOTDIR
error on POSIX.
fs.stat(path, callback)#
path
<string> | <Buffer>callback
<Function>err
<Error>stats
<fs.Stats>
Asynchronous stat(2). The callback gets two arguments (err, stats)
where
stats
is an fs.Stats
object.
In case of an error, the err.code
will be one of Common System Errors.
Using fs.stat()
to check for the existence of a file before calling
fs.open()
, fs.readFile()
or fs.writeFile()
is not recommended.
Instead, user code should open/read/write the file directly and handle the
error raised if the file is not available.
To check if a file exists without manipulating it afterwards, fs.access()
is recommended.
fs.statSync(path)#
Synchronous stat(2). Returns an instance of fs.Stats
.
fs.symlink(target, path[, type], callback)#
Asynchronous symlink(2). No arguments other than a possible exception are given
to the completion callback. The type
argument can be set to 'dir'
,
'file'
, or 'junction'
(default is 'file'
) and is only available on
Windows (ignored on other platforms). Note that Windows junction points require
the destination path to be absolute. When using 'junction'
, the target
argument will automatically be normalized to absolute path.
Here is an example below:
fs.symlink('./foo', './new-port', callback);
It creates a symbolic link named "new-port" that points to "foo".
fs.symlinkSync(target, path[, type])#
Synchronous symlink(2). Returns undefined
.
fs.truncate(path, len, callback)#
path
<string> | <Buffer>len
<integer> default =0
callback
<Function>err
<Error>
Asynchronous truncate(2). No arguments other than a possible exception are
given to the completion callback. A file descriptor can also be passed as the
first argument. In this case, fs.ftruncate()
is called.
fs.truncateSync(path, len)#
Synchronous truncate(2). Returns undefined
. A file descriptor can also be
passed as the first argument. In this case, fs.ftruncateSync()
is called.
fs.unlink(path, callback)#
path
<string> | <Buffer>callback
<Function>err
<Error>
Asynchronous unlink(2). No arguments other than a possible exception are given to the completion callback.
fs.unlinkSync(path)#
Synchronous unlink(2). Returns undefined
.
fs.unwatchFile(filename[, listener])#
Stop watching for changes on filename
. If listener
is specified, only that
particular listener is removed. Otherwise, all listeners are removed and you
have effectively stopped watching filename
.
Calling fs.unwatchFile()
with a filename that is not being watched is a
no-op, not an error.
Note: fs.watch()
is more efficient than fs.watchFile()
and fs.unwatchFile()
.
fs.watch()
should be used instead of fs.watchFile()
and fs.unwatchFile()
when possible.
fs.utimes(path, atime, mtime, callback)#
Change file timestamps of the file referenced by the supplied path.
Note: the arguments atime
and mtime
of the following related functions
follow these rules:
- The value should be a Unix timestamp in seconds. For example,
Date.now()
returns milliseconds, so it should be divided by 1000 before passing it in. - If the value is a numeric string like
'123456789'
, the value will get converted to the corresponding number. - If the value is
NaN
orInfinity
, the value will get converted toDate.now() / 1000
.
fs.utimesSync(path, atime, mtime)#
Synchronous version of fs.utimes()
. Returns undefined
.
fs.watch(filename[, options][, listener])#
filename
<string> | <Buffer>options
<string> | <Object>persistent
<boolean> Indicates whether the process should continue to run as long as files are being watched. default =true
recursive
<boolean> Indicates whether all subdirectories should be watched, or only the current directory. The applies when a directory is specified, and only on supported platforms (See Caveats). default =false
encoding
<string> Specifies the character encoding to be used for the filename passed to the listener. default ='utf8'
listener
<Function>
Watch for changes on filename
, where filename
is either a file or a
directory. The returned object is a fs.FSWatcher
.
The second argument is optional. If options
is provided as a string, it
specifies the encoding
. Otherwise options
should be passed as an object.
The listener callback gets two arguments (eventType, filename)
. eventType
is either
'rename'
or 'change'
, and filename
is the name of the file which triggered
the event.
Note that on most platforms, 'rename'
is emitted whenever a filename appears
or disappears in the directory.
Also note the listener callback is attached to the 'change'
event fired by
fs.FSWatcher
, but it is not the same thing as the 'change'
value of
eventType
.
Caveats#
The fs.watch
API is not 100% consistent across platforms, and is
unavailable in some situations.
The recursive option is only supported on macOS and Windows.
Availability#
This feature depends on the underlying operating system providing a way to be notified of filesystem changes.
- On Linux systems, this uses
inotify
- On BSD systems, this uses
kqueue
- On macOS, this uses
kqueue
for files andFSEvents
for directories. - On SunOS systems (including Solaris and SmartOS), this uses
event ports
. - On Windows systems, this feature depends on
ReadDirectoryChangesW
. - On Aix systems, this feature depends on
AHAFS
, which must be enabled.
If the underlying functionality is not available for some reason, then
fs.watch
will not be able to function. For example, watching files or
directories can be unreliable, and in some cases impossible, on network file
systems (NFS, SMB, etc), or host file systems when using virtualization software
such as Vagrant, Docker, etc.
You can still use fs.watchFile
, which uses stat polling, but it is slower and
less reliable.
Inodes#
On Linux and macOS systems, fs.watch()
resolves the path to an inode and
watches the inode. If the watched path is deleted and recreated, it is assigned
a new inode. The watch will emit an event for the delete but will continue
watching the original inode. Events for the new inode will not be emitted.
This is expected behavior.
On AIX, save and close of a file being watched causes two notifications - one for adding new content, and one for truncation. Moreover, save and close operations on some platforms cause inode changes that force watch operations to become invalid and ineffective. AIX retains inode for the lifetime of a file, that way though this is different from Linux / OS X, this improves the usability of file watching. This is expected behavior.
Filename Argument#
Providing filename
argument in the callback is only supported on Linux and
Windows. Even on supported platforms, filename
is not always guaranteed to
be provided. Therefore, don't assume that filename
argument is always
provided in the callback, and have some fallback logic if it is null.
fs.watch('somedir', (eventType, filename) => {
console.log(`event type is: ${eventType}`);
if (filename) {
console.log(`filename provided: ${filename}`);
} else {
console.log('filename not provided');
}
});
fs.watchFile(filename[, options], listener)#
filename
<string> | <Buffer>options
<Object>listener
<Function>current
<fs.Stats>previous
<fs.Stats>
Watch for changes on filename
. The callback listener
will be called each
time the file is accessed.
The options
argument may be omitted. If provided, it should be an object. The
options
object may contain a boolean named persistent
that indicates
whether the process should continue to run as long as files are being watched.
The options
object may specify an interval
property indicating how often the
target should be polled in milliseconds. The default is
{ persistent: true, interval: 5007 }
.
The listener
gets two arguments the current stat object and the previous
stat object:
fs.watchFile('message.text', (curr, prev) => {
console.log(`the current mtime is: ${curr.mtime}`);
console.log(`the previous mtime was: ${prev.mtime}`);
});
These stat objects are instances of fs.Stat
.
If you want to be notified when the file was modified, not just accessed,
you need to compare curr.mtime
and prev.mtime
.
Note: when an fs.watchFile
operation results in an ENOENT
error, it will
invoke the listener once, with all the fields zeroed (or, for dates, the Unix
Epoch). In Windows, blksize
and blocks
fields will be undefined
, instead
of zero. If the file is created later on, the listener will be called again,
with the latest stat objects. This is a change in functionality since v0.10.
Note: fs.watch()
is more efficient than fs.watchFile
and
fs.unwatchFile
. fs.watch
should be used instead of fs.watchFile
and
fs.unwatchFile
when possible.
Note: When a file being watched by fs.watchFile()
disappears and reappears,
then the previousStat
reported in the second callback event (the file's
reappearance) will be the same as the previousStat
of the first callback
event (its disappearance).
This happens when:
- the file is deleted, followed by a restore
- the file is renamed twice - the second time back to its original name
fs.write(fd, buffer[, offset[, length[, position]]], callback)#
fd
<integer>buffer
<Buffer>offset
<integer>length
<integer>position
<integer>callback
<Function>err
<Error>bytesWritten
<integer>buffer
<Buffer> | <Uint8Array>
Write buffer
to the file specified by fd
.
offset
determines the part of the buffer to be written, and length
is
an integer specifying the number of bytes to write.
position
refers to the offset from the beginning of the file where this data
should be written. If typeof position !== 'number'
, the data will be written
at the current position. See pwrite(2).
The callback will be given three arguments (err, written, buffer)
where
written
specifies how many bytes were written from buffer
.
Note that it is unsafe to use fs.write
multiple times on the same file
without waiting for the callback. For this scenario,
fs.createWriteStream
is strongly recommended.
On Linux, positional writes don't work when the file is opened in append mode. The kernel ignores the position argument and always appends the data to the end of the file.
fs.write(fd, string[, position[, encoding]], callback)#
fd
<integer>string
<string>position
<integer>encoding
<string>callback
<Function>
Write string
to the file specified by fd
. If string
is not a string, then
the value will be coerced to one.
position
refers to the offset from the beginning of the file where this data
should be written. If typeof position !== 'number'
the data will be written at
the current position. See pwrite(2).
encoding
is the expected string encoding.
The callback will receive the arguments (err, written, string)
where written
specifies how many bytes the passed string required to be written. Note that
bytes written is not the same as string characters. See Buffer.byteLength
.
Unlike when writing buffer
, the entire string must be written. No substring
may be specified. This is because the byte offset of the resulting data may not
be the same as the string offset.
Note that it is unsafe to use fs.write
multiple times on the same file
without waiting for the callback. For this scenario,
fs.createWriteStream
is strongly recommended.
On Linux, positional writes don't work when the file is opened in append mode. The kernel ignores the position argument and always appends the data to the end of the file.
fs.writeFile(file, data[, options], callback)#
file
<string> | <Buffer> | <integer> filename or file descriptordata
<string> | <Buffer>options
<Object> | <string>callback
<Function>err
<Error>
Asynchronously writes data to a file, replacing the file if it already exists.
data
can be a string or a buffer.
The encoding
option is ignored if data
is a buffer. It defaults
to 'utf8'
.
Example:
fs.writeFile('message.txt', 'Hello Node.js', (err) => {
if (err) throw err;
console.log('The file has been saved!');
});
If options
is a string, then it specifies the encoding. Example:
fs.writeFile('message.txt', 'Hello Node.js', 'utf8', callback);
Any specified file descriptor has to support writing.
Note that it is unsafe to use fs.writeFile
multiple times on the same file
without waiting for the callback. For this scenario,
fs.createWriteStream
is strongly recommended.
Note: If a file descriptor is specified as the file
, it will not be closed
automatically.
fs.writeFileSync(file, data[, options])#
file
<string> | <Buffer> | <integer> filename or file descriptordata
<string> | <Buffer>options
<Object> | <string>
The synchronous version of fs.writeFile()
. Returns undefined
.
fs.writeSync(fd, buffer[, offset[, length[, position]]])#
fs.writeSync(fd, string[, position[, encoding]])#
Synchronous versions of fs.write()
. Returns the number of bytes written.
FS Constants#
The following constants are exported by fs.constants
. Note: Not every
constant will be available on every operating system.
File Access Constants#
The following constants are meant for use with fs.access()
.
Constant | Description |
---|---|
F_OK |
Flag indicating that the file is visible to the calling process. |
R_OK |
Flag indicating that the file can be read by the calling process. |
W_OK |
Flag indicating that the file can be written by the calling process. |
X_OK |
Flag indicating that the file can be executed by the calling process. |
File Open Constants#
The following constants are meant for use with fs.open()
.
Constant | Description |
---|---|
O_RDONLY |
Flag indicating to open a file for read-only access. |
O_WRONLY |
Flag indicating to open a file for write-only access. |
O_RDWR |
Flag indicating to open a file for read-write access. |
O_CREAT |
Flag indicating to create the file if it does not already exist. |
O_EXCL |
Flag indicating that opening a file should fail if the
O_CREAT flag is set and the file already exists. |
O_NOCTTY |
Flag indicating that if path identifies a terminal device, opening the path shall not cause that terminal to become the controlling terminal for the process (if the process does not already have one). |
O_TRUNC |
Flag indicating that if the file exists and is a regular file, and the file is opened successfully for write access, its length shall be truncated to zero. |
O_APPEND |
Flag indicating that data will be appended to the end of the file. |
O_DIRECTORY |
Flag indicating that the open should fail if the path is not a directory. |
O_NOATIME |
Flag indicating reading accesses to the file system will no longer
result in an update to the atime information associated with the file.
This flag is available on Linux operating systems only. |
O_NOFOLLOW |
Flag indicating that the open should fail if the path is a symbolic link. |
O_SYNC |
Flag indicating that the file is opened for synchronous I/O. |
O_SYMLINK |
Flag indicating to open the symbolic link itself rather than the resource it is pointing to. |
O_DIRECT |
When set, an attempt will be made to minimize caching effects of file I/O. |
O_NONBLOCK |
Flag indicating to open the file in nonblocking mode when possible. |
File Type Constants#
The following constants are meant for use with the fs.Stats
object's
mode
property for determining a file's type.
Constant | Description |
---|---|
S_IFMT |
Bit mask used to extract the file type code. |
S_IFREG |
File type constant for a regular file. |
S_IFDIR |
File type constant for a directory. |
S_IFCHR |
File type constant for a character-oriented device file. |
S_IFBLK |
File type constant for a block-oriented device file. |
S_IFIFO |
File type constant for a FIFO/pipe. |
S_IFLNK |
File type constant for a symbolic link. |
S_IFSOCK |
File type constant for a socket. |
File Mode Constants#
The following constants are meant for use with the fs.Stats
object's
mode
property for determining the access permissions for a file.
Constant | Description |
---|---|
S_IRWXU |
File mode indicating readable, writable and executable by owner. |
S_IRUSR |
File mode indicating readable by owner. |
S_IWUSR |
File mode indicating writable by owner. |
S_IXUSR |
File mode indicating executable by owner. |
S_IRWXG |
File mode indicating readable, writable and executable by group. |
S_IRGRP |
File mode indicating readable by group. |
S_IWGRP |
File mode indicating writable by group. |
S_IXGRP |
File mode indicating executable by group. |
S_IRWXO |
File mode indicating readable, writable and executable by others. |
S_IROTH |
File mode indicating readable by others. |
S_IWOTH |
File mode indicating writable by others. |
S_IXOTH |
File mode indicating executable by others. |
Global Objects#
These objects are available in all modules. Some of these objects aren't actually in the global scope but in the module scope - this will be noted.
The objects listed here are specific to Node.js. There are a number of built-in objects that are part of the JavaScript language itself, which are also globally accessible.
Class: Buffer#
Used to handle binary data. See the buffer section.
__dirname#
The directory name of the current module. This the same as the
path.dirname()
of the __filename
.
__dirname
is not actually a global but rather local to each module.
Example: running node example.js
from /Users/mjr
console.log(__dirname);
// Prints: /Users/mjr
console.log(path.dirname(__filename));
// Prints: /Users/mjr
__filename#
The file name of the current module. This is the resolved absolute path of the current module file.
For a main program this is not necessarily the same as the file name used in the command line.
See __dirname
for the directory name of the current module.
__filename
is not actually a global but rather local to each module.
Examples:
Running node example.js
from /Users/mjr
console.log(__filename);
// Prints: /Users/mjr/example.js
console.log(__dirname);
// Prints: /Users/mjr
Given two modules: a
and b
, where b
is a dependency of
a
and there is a directory structure of:
/Users/mjr/app/a.js
/Users/mjr/app/node_modules/b/b.js
References to __filename
within b.js
will return
/Users/mjr/app/node_modules/b/b.js
while references to __filename
within
a.js
will return /Users/mjr/app/a.js
.
clearImmediate(immediateObject)#
clearImmediate
is described in the timers section.
clearInterval(intervalObject)#
clearInterval
is described in the timers section.
clearTimeout(timeoutObject)#
clearTimeout
is described in the timers section.
console#
Used to print to stdout and stderr. See the console
section.
exports#
A reference to the module.exports
that is shorter to type.
See module system documentation for details on when to use exports
and
when to use module.exports
.
exports
is not actually a global but rather local to each module.
See the module system documentation for more information.
global#
- <Object> The global namespace object.
In browsers, the top-level scope is the global scope. That means that in
browsers if you're in the global scope var something
will define a global
variable. In Node.js this is different. The top-level scope is not the global
scope; var something
inside an Node.js module will be local to that module.
module#
A reference to the current module. In particular
module.exports
is used for defining what a module exports and makes
available through require()
.
module
is not actually a global but rather local to each module.
See the module system documentation for more information.
process#
The process object. See the process
object section.
require()#
To require modules. See the Modules section. require
is not actually a
global but rather local to each module.
require.cache#
Modules are cached in this object when they are required. By deleting a key
value from this object, the next require
will reload the module. Note that
this does not apply to native addons, for which reloading will result in an
Error.
require.extensions#
Instruct require
on how to handle certain file extensions.
Process files with the extension .sjs
as .js
:
require.extensions['.sjs'] = require.extensions['.js'];
Deprecated In the past, this list has been used to load non-JavaScript modules into Node.js by compiling them on-demand. However, in practice, there are much better ways to do this, such as loading modules via some other Node.js program, or compiling them to JavaScript ahead of time.
Since the Module system is locked, this feature will probably never go away. However, it may have subtle bugs and complexities that are best left untouched.
require.resolve()#
Use the internal require()
machinery to look up the location of a module,
but rather than loading the module, just return the resolved filename.
setImmediate(callback[, ...args])#
setImmediate
is described in the timers section.
setInterval(callback, delay[, ...args])#
setInterval
is described in the timers section.
setTimeout(callback, delay[, ...args])#
setTimeout
is described in the timers section.
HTTP#
To use the HTTP server and client one must require('http')
.
The HTTP interfaces in Node.js are designed to support many features of the protocol which have been traditionally difficult to use. In particular, large, possibly chunk-encoded, messages. The interface is careful to never buffer entire requests or responses--the user is able to stream data.
HTTP message headers are represented by an object like this:
{ 'content-length': '123',
'content-type': 'text/plain',
'connection': 'keep-alive',
'host': 'mysite.com',
'accept': '*/*' }
Keys are lowercased. Values are not modified.
In order to support the full spectrum of possible HTTP applications, Node.js's HTTP API is very low-level. It deals with stream handling and message parsing only. It parses a message into headers and body but it does not parse the actual headers or the body.
See message.headers
for details on how duplicate headers are handled.
The raw headers as they were received are retained in the rawHeaders
property, which is an array of [key, value, key2, value2, ...]
. For
example, the previous message header object might have a rawHeaders
list like the following:
[ 'ConTent-Length', '123456',
'content-LENGTH', '123',
'content-type', 'text/plain',
'CONNECTION', 'keep-alive',
'Host', 'mysite.com',
'accepT', '*/*' ]
Class: http.Agent#
An Agent
is responsible for managing connection persistence
and reuse for HTTP clients. It maintains a queue of pending requests
for a given host and port, reusing a single socket connection for each
until the queue is empty, at which time the socket is either destroyed
or put into a pool where it is kept to be used again for requests to the
same host and port. Whether it is destroyed or pooled depends on the
keepAlive
option.
Pooled connections have TCP Keep-Alive enabled for them, but servers may
still close idle connections, in which case they will be removed from the
pool and a new connection will be made when a new HTTP request is made for
that host and port. Servers may also refuse to allow multiple requests
over the same connection, in which case the connection will have to be
remade for every request and cannot be pooled. The Agent
will still make
the requests to that server, but each one will occur over a new connection.
When a connection is closed by the client or the server, it is removed from the pool. Any unused sockets in the pool will be unrefed so as not to keep the Node.js process running when there are no outstanding requests. (see socket.unref()).
It is good practice, to destroy()
an Agent
instance when it is no
longer in use, because unused sockets consume OS resources.
Sockets are removed from an agent's pool when the socket emits either
a 'close'
event or an 'agentRemove'
event. This means that if
you intend to keep one HTTP request open for a long time and don't
want it to stay in the pool you can do something along the lines of:
http.get(options, (res) => {
// Do stuff
}).on('socket', (socket) => {
socket.emit('agentRemove');
});
You may also use an agent for an individual request. By providing
{agent: false}
as an option to the http.get()
or http.request()
functions, a one-time use Agent
with default options will be used
for the client connection.
agent:false
:
http.get({
hostname: 'localhost',
port: 80,
path: '/',
agent: false // create a new agent just for this one request
}, (res) => {
// Do stuff with response
});
new Agent(options)#
options
<Object> Set of configurable options to set on the agent. Can have the following fields:keepAlive
<boolean> Keep sockets around even when there are no outstanding requests, so they can be used for future requests without having to reestablish a TCP connection. Default =false
keepAliveMsecs
<Integer> When using thekeepAlive
option, specifies the initial delay for TCP Keep-Alive packets. Ignored when thekeepAlive
option isfalse
orundefined
. Default =1000
.maxSockets
<number> Maximum number of sockets to allow per host. Default =Infinity
.maxFreeSockets
<number> Maximum number of sockets to leave open in a free state. Only relevant ifkeepAlive
is set totrue
. Default =256
.
The default http.globalAgent
that is used by http.request()
has all
of these values set to their respective defaults.
To configure any of them, you must create your own http.Agent
instance.
const http = require('http');
const keepAliveAgent = new http.Agent({ keepAlive: true });
options.agent = keepAliveAgent;
http.request(options, onResponseCallback);
agent.createConnection(options[, callback])#
options
<Object> Options containing connection details. Checknet.createConnection()
for the format of the optionscallback
<Function> Callback function that receives the created socket- Returns: <net.Socket>
Produces a socket/stream to be used for HTTP requests.
By default, this function is the same as net.createConnection()
. However,
custom agents may override this method in case greater flexibility is desired.
A socket/stream can be supplied in one of two ways: by returning the
socket/stream from this function, or by passing the socket/stream to callback
.
callback
has a signature of (err, stream)
.
agent.keepSocketAlive(socket)#
socket
<net.Socket>
Called when socket
is detached from a request and could be persisted by the
Agent. Default behavior is to:
socket.unref();
socket.setKeepAlive(agent.keepAliveMsecs);
This method can be overridden by a particular Agent
subclass. If this
method returns a falsy value, the socket will be destroyed instead of persisting
it for use with the next request.
agent.reuseSocket(socket, request)#
socket
<net.Socket>request
<http.ClientRequest>
Called when socket
is attached to request
after being persisted because of
the keep-alive options. Default behavior is to:
socket.ref();
This method can be overridden by a particular Agent
subclass.
agent.destroy()#
Destroy any sockets that are currently in use by the agent.
It is usually not necessary to do this. However, if you are using an
agent with keepAlive
enabled, then it is best to explicitly shut down
the agent when you know that it will no longer be used. Otherwise,
sockets may hang open for quite a long time before the server
terminates them.
agent.freeSockets#
An object which contains arrays of sockets currently awaiting use by
the agent when keepAlive
is enabled. Do not modify.
agent.getName(options)#
Get a unique name for a set of request options, to determine whether a
connection can be reused. For an HTTP agent, this returns
host:port:localAddress
. For an HTTPS agent, the name includes the
CA, cert, ciphers, and other HTTPS/TLS-specific options that determine
socket reusability.
agent.maxFreeSockets#
By default set to 256. For agents with keepAlive
enabled, this
sets the maximum number of sockets that will be left open in the free
state.
agent.maxSockets#
By default set to Infinity. Determines how many concurrent sockets the agent can have open per origin. Origin is either a 'host:port' or 'host:port:localAddress' combination.
agent.requests#
An object which contains queues of requests that have not yet been assigned to sockets. Do not modify.
agent.sockets#
An object which contains arrays of sockets currently in use by the agent. Do not modify.
Class: http.ClientRequest#
This object is created internally and returned from http.request()
. It
represents an in-progress request whose header has already been queued. The
header is still mutable using the setHeader(name, value)
, getHeader(name)
,
removeHeader(name)
API. The actual header will be sent along with the first
data chunk or when closing the connection.
To get the response, add a listener for 'response'
to the request object.
'response'
will be emitted from the request object when the response
headers have been received. The 'response'
event is executed with one
argument which is an instance of http.IncomingMessage
.
During the 'response'
event, one can add listeners to the
response object; particularly to listen for the 'data'
event.
If no 'response'
handler is added, then the response will be
entirely discarded. However, if you add a 'response'
event handler,
then you must consume the data from the response object, either by
calling response.read()
whenever there is a 'readable'
event, or
by adding a 'data'
handler, or by calling the .resume()
method.
Until the data is consumed, the 'end'
event will not fire. Also, until
the data is read it will consume memory that can eventually lead to a
'process out of memory' error.
Note: Node.js does not check whether Content-Length and the length of the body which has been transmitted are equal or not.
The request implements the Writable Stream interface. This is an
EventEmitter
with the following events:
Event: 'abort'#
Emitted when the request has been aborted by the client. This event is only
emitted on the first call to abort()
.
Event: 'connect'#
response
<http.IncomingMessage>socket
<net.Socket>head
<Buffer>
Emitted each time a server responds to a request with a CONNECT
method. If this
event is not being listened for, clients receiving a CONNECT
method will have
their connections closed.
A client and server pair that shows you how to listen for the 'connect'
event:
const http = require('http');
const net = require('net');
const url = require('url');
// Create an HTTP tunneling proxy
const proxy = http.createServer((req, res) => {
res.writeHead(200, {'Content-Type': 'text/plain'});
res.end('okay');
});
proxy.on('connect', (req, cltSocket, head) => {
// connect to an origin server
const srvUrl = url.parse(`http://${req.url}`);
const srvSocket = net.connect(srvUrl.port, srvUrl.hostname, () => {
cltSocket.write('HTTP/1.1 200 Connection Established\r\n' +
'Proxy-agent: Node.js-Proxy\r\n' +
'\r\n');
srvSocket.write(head);
srvSocket.pipe(cltSocket);
cltSocket.pipe(srvSocket);
});
});
// now that proxy is running
proxy.listen(1337, '127.0.0.1', () => {
// make a request to a tunneling proxy
const options = {
port: 1337,
hostname: '127.0.0.1',
method: 'CONNECT',
path: 'www.google.com:80'
};
const req = http.request(options);
req.end();
req.on('connect', (res, socket, head) => {
console.log('got connected!');
// make a request over an HTTP tunnel
socket.write('GET / HTTP/1.1\r\n' +
'Host: www.google.com:80\r\n' +
'Connection: close\r\n' +
'\r\n');
socket.on('data', (chunk) => {
console.log(chunk.toString());
});
socket.on('end', () => {
proxy.close();
});
});
});
Event: 'continue'#
Emitted when the server sends a '100 Continue' HTTP response, usually because the request contained 'Expect: 100-continue'. This is an instruction that the client should send the request body.
Event: 'response'#
response
<http.IncomingMessage>
Emitted when a response is received to this request. This event is emitted only once.
Event: 'socket'#
socket
<net.Socket>
Emitted after a socket is assigned to this request.
Event: 'upgrade'#
response
<http.IncomingMessage>socket
<net.Socket>head
<Buffer>
Emitted each time a server responds to a request with an upgrade. If this event is not being listened for, clients receiving an upgrade header will have their connections closed.
A client server pair that show you how to listen for the 'upgrade'
event.
const http = require('http');
// Create an HTTP server
const srv = http.createServer((req, res) => {
res.writeHead(200, {'Content-Type': 'text/plain'});
res.end('okay');
});
srv.on('upgrade', (req, socket, head) => {
socket.write('HTTP/1.1 101 Web Socket Protocol Handshake\r\n' +
'Upgrade: WebSocket\r\n' +
'Connection: Upgrade\r\n' +
'\r\n');
socket.pipe(socket); // echo back
});
// now that server is running
srv.listen(1337, '127.0.0.1', () => {
// make a request
const options = {
port: 1337,
hostname: '127.0.0.1',
headers: {
'Connection': 'Upgrade',
'Upgrade': 'websocket'
}
};
const req = http.request(options);
req.end();
req.on('upgrade', (res, socket, upgradeHead) => {
console.log('got upgraded!');
socket.end();
process.exit(0);
});
});
request.abort()#
Marks the request as aborting. Calling this will cause remaining data in the response to be dropped and the socket to be destroyed.
request.aborted#
If a request has been aborted, this value is the time when the request was aborted, in milliseconds since 1 January 1970 00:00:00 UTC.
request.end([data][, encoding][, callback])#
data
<string> | <Buffer>encoding
<string>callback
<Function>
Finishes sending the request. If any parts of the body are
unsent, it will flush them to the stream. If the request is
chunked, this will send the terminating '0\r\n\r\n'
.
If data
is specified, it is equivalent to calling
request.write(data, encoding)
followed by request.end(callback)
.
If callback
is specified, it will be called when the request stream
is finished.
request.flushHeaders()#
Flush the request headers.
For efficiency reasons, Node.js normally buffers the request headers until you
call request.end()
or write the first chunk of request data. It then tries
hard to pack the request headers and data into a single TCP packet.
That's usually what you want (it saves a TCP round-trip) but not when the first
data is not sent until possibly much later. request.flushHeaders()
lets you bypass
the optimization and kickstart the request.
request.setNoDelay([noDelay])#
noDelay
<boolean>
Once a socket is assigned to this request and is connected
socket.setNoDelay()
will be called.
request.setSocketKeepAlive([enable][, initialDelay])#
Once a socket is assigned to this request and is connected
socket.setKeepAlive()
will be called.
request.setTimeout(timeout[, callback])#
timeout
<number> Milliseconds before a request times out.callback
<Function> Optional function to be called when a timeout occurs. Same as binding to thetimeout
event.
Once a socket is assigned to this request and is connected
socket.setTimeout()
will be called.
Returns request
.
request.write(chunk[, encoding][, callback])#
chunk
<string> | <Buffer>encoding
<string>callback
<Function>
Sends a chunk of the body. By calling this method
many times, the user can stream a request body to a
server--in that case it is suggested to use the
['Transfer-Encoding', 'chunked']
header line when
creating the request.
The encoding
argument is optional and only applies when chunk
is a string.
Defaults to 'utf8'
.
The callback
argument is optional and will be called when this chunk of data
is flushed.
Returns request
.
Class: http.Server#
This class inherits from net.Server
and has the following additional events:
Event: 'checkContinue'#
request
<http.IncomingMessage>response
<http.ServerResponse>
Emitted each time a request with an HTTP Expect: 100-continue
is received.
If this event is not listened for, the server will automatically respond
with a 100 Continue
as appropriate.
Handling this event involves calling response.writeContinue()
if the client
should continue to send the request body, or generating an appropriate HTTP
response (e.g. 400 Bad Request) if the client should not continue to send the
request body.
Note that when this event is emitted and handled, the 'request'
event will
not be emitted.
Event: 'checkExpectation'#
request
<http.ClientRequest>response
<http.ServerResponse>
Emitted each time a request with an HTTP Expect
header is received, where the
value is not 100-continue
. If this event is not listened for, the server will
automatically respond with a 417 Expectation Failed
as appropriate.
Note that when this event is emitted and handled, the 'request'
event will
not be emitted.
Event: 'clientError'#
exception
<Error>socket
<net.Socket>
If a client connection emits an 'error'
event, it will be forwarded here.
Listener of this event is responsible for closing/destroying the underlying
socket. For example, one may wish to more gracefully close the socket with an
HTTP '400 Bad Request' response instead of abruptly severing the connection.
Default behavior is to destroy the socket immediately on malformed request.
socket
is the net.Socket
object that the error originated from.
const http = require('http');
const server = http.createServer((req, res) => {
res.end();
});
server.on('clientError', (err, socket) => {
socket.end('HTTP/1.1 400 Bad Request\r\n\r\n');
});
server.listen(8000);
When the 'clientError'
event occurs, there is no request
or response
object, so any HTTP response sent, including response headers and payload,
must be written directly to the socket
object. Care must be taken to
ensure the response is a properly formatted HTTP response message.
Event: 'close'#
Emitted when the server closes.
Event: 'connect'#
request
<http.IncomingMessage> Arguments for the HTTP request, as it is in the'request'
eventsocket
<net.Socket> Network socket between the server and clienthead
<Buffer> The first packet of the tunneling stream (may be empty)
Emitted each time a client requests an HTTP CONNECT
method. If this event is
not listened for, then clients requesting a CONNECT
method will have their
connections closed.
After this event is emitted, the request's socket will not have a 'data'
event listener, meaning you will need to bind to it in order to handle data
sent to the server on that socket.
Event: 'connection'#
socket
<net.Socket>
When a new TCP stream is established. socket
is an object of type
net.Socket
. Usually users will not want to access this event. In
particular, the socket will not emit 'readable'
events because of how
the protocol parser attaches to the socket. The socket
can also be
accessed at request.connection
.
Event: 'request'#
request
<http.IncomingMessage>response
<http.ServerResponse>
Emitted each time there is a request. Note that there may be multiple requests per connection (in the case of HTTP Keep-Alive connections).
Event: 'upgrade'#
request
<http.IncomingMessage> Arguments for the HTTP request, as it is in the'request'
eventsocket
<net.Socket> Network socket between the server and clienthead
<Buffer> The first packet of the upgraded stream (may be empty)
Emitted each time a client requests an HTTP upgrade. If this event is not listened for, then clients requesting an upgrade will have their connections closed.
After this event is emitted, the request's socket will not have a 'data'
event listener, meaning you will need to bind to it in order to handle data
sent to the server on that socket.
server.close([callback])#
callback
<Function>
Stops the server from accepting new connections. See net.Server.close()
.
server.listen(handle[, callback])#
handle
<Object>callback
<Function>
The handle
object can be set to either a server or socket (anything
with an underlying _handle
member), or a {fd: <n>}
object.
This will cause the server to accept connections on the specified handle, but it is presumed that the file descriptor or handle has already been bound to a port or domain socket.
Listening on a file descriptor is not supported on Windows.
This function is asynchronous. callback
will be added as a listener for the
'listening'
event. See also net.Server.listen()
.
Returns server
.
Note: The server.listen()
method may be called multiple times. Each
subsequent call will re-open the server using the provided options.
server.listen(path[, callback])#
path
<string>callback
<Function>
Start a UNIX socket server listening for connections on the given path
.
This function is asynchronous. callback
will be added as a listener for the
'listening'
event. See also net.Server.listen(path)
.
Note: The server.listen()
method may be called multiple times. Each
subsequent call will re-open the server using the provided options.
server.listen([port][, hostname][, backlog][, callback])#
port
<number>hostname
<string>backlog
<number>callback
<Function>
Begin accepting connections on the specified port
and hostname
. If the
hostname
is omitted, the server will accept connections on any IPv6 address
(::
) when IPv6 is available, or any IPv4 address (0.0.0.0
) otherwise.
Omit the port argument, or use a port value of 0
, to have the operating system
assign a random port, which can be retrieved by using server.address().port
after the 'listening'
event has been emitted.
To listen to a unix socket, supply a filename instead of port and hostname.
backlog
is the maximum length of the queue of pending connections.
The actual length will be determined by your OS through sysctl settings such as
tcp_max_syn_backlog
and somaxconn
on linux. The default value of this
parameter is 511 (not 512).
This function is asynchronous. callback
will be added as a listener for the
'listening'
event. See also net.Server.listen(port)
.
Note: The server.listen()
method may be called multiple times. Each
subsequent call will re-open the server using the provided options.
server.listening#
A Boolean indicating whether or not the server is listening for connections.
server.maxHeadersCount#
Limits maximum incoming headers count, equal to 1000 by default. If set to 0 - no limit will be applied.
server.setTimeout(msecs, callback)#
msecs
<number>callback
<Function>
Sets the timeout value for sockets, and emits a 'timeout'
event on
the Server object, passing the socket as an argument, if a timeout
occurs.
If there is a 'timeout'
event listener on the Server object, then it
will be called with the timed-out socket as an argument.
By default, the Server's timeout value is 2 minutes, and sockets are
destroyed automatically if they time out. However, if you assign a
callback to the Server's 'timeout'
event, then you are responsible
for handling socket timeouts.
Returns server
.
server.timeout#
- <Number> Default = 120000 (2 minutes)
The number of milliseconds of inactivity before a socket is presumed to have timed out.
Note that the socket timeout logic is set up on connection, so changing this value only affects new connections to the server, not any existing connections.
Set to 0 to disable any kind of automatic timeout behavior on incoming connections.
Class: http.ServerResponse#
This object is created internally by an HTTP server--not by the user. It is
passed as the second parameter to the 'request'
event.
The response implements, but does not inherit from, the Writable Stream
interface. This is an EventEmitter
with the following events:
Event: 'close'#
Indicates that the underlying connection was terminated before
response.end()
was called or able to flush.
Event: 'finish'#
Emitted when the response has been sent. More specifically, this event is emitted when the last segment of the response headers and body have been handed off to the operating system for transmission over the network. It does not imply that the client has received anything yet.
After this event, no more events will be emitted on the response object.
response.addTrailers(headers)#
headers
<Object>
This method adds HTTP trailing headers (a header but at the end of the message) to the response.
Trailers will only be emitted if chunked encoding is used for the response; if it is not (e.g. if the request was HTTP/1.0), they will be silently discarded.
Note that HTTP requires the Trailer
header to be sent if you intend to
emit trailers, with a list of the header fields in its value. E.g.,
response.writeHead(200, { 'Content-Type': 'text/plain',
'Trailer': 'Content-MD5' });
response.write(fileData);
response.addTrailers({'Content-MD5': '7895bf4b8828b55ceaf47747b4bca667'});
response.end();
Attempting to set a header field name or value that contains invalid characters
will result in a TypeError
being thrown.
response.end([data][, encoding][, callback])#
data
<string> | <Buffer>encoding
<string>callback
<Function>
This method signals to the server that all of the response headers and body
have been sent; that server should consider this message complete.
The method, response.end()
, MUST be called on each response.
If data
is specified, it is equivalent to calling
response.write(data, encoding)
followed by response.end(callback)
.
If callback
is specified, it will be called when the response stream
is finished.
response.finished#
Boolean value that indicates whether the response has completed. Starts
as false
. After response.end()
executes, the value will be true
.
response.getHeader(name)#
Reads out a header that's already been queued but not sent to the client. Note that the name is case insensitive.
Example:
const contentType = response.getHeader('content-type');
response.headersSent#
Boolean (read-only). True if headers were sent, false otherwise.
response.removeHeader(name)#
name
<string>
Removes a header that's queued for implicit sending.
Example:
response.removeHeader('Content-Encoding');
response.sendDate#
When true, the Date header will be automatically generated and sent in the response if it is not already present in the headers. Defaults to true.
This should only be disabled for testing; HTTP requires the Date header in responses.
response.setHeader(name, value)#
Sets a single header value for implicit headers. If this header already exists in the to-be-sent headers, its value will be replaced. Use an array of strings here if you need to send multiple headers with the same name.
Example:
response.setHeader('Content-Type', 'text/html');
or
response.setHeader('Set-Cookie', ['type=ninja', 'language=javascript']);
Attempting to set a header field name or value that contains invalid characters
will result in a TypeError
being thrown.
When headers have been set with response.setHeader()
, they will be merged with
any headers passed to response.writeHead()
, with the headers passed to
response.writeHead()
given precedence.
// returns content-type = text/plain
const server = http.createServer((req, res) => {
res.setHeader('Content-Type', 'text/html');
res.setHeader('X-Foo', 'bar');
res.writeHead(200, {'Content-Type': 'text/plain'});
res.end('ok');
});
response.setTimeout(msecs, callback)#
msecs
<number>callback
<Function>
Sets the Socket's timeout value to msecs
. If a callback is
provided, then it is added as a listener on the 'timeout'
event on
the response object.
If no 'timeout'
listener is added to the request, the response, or
the server, then sockets are destroyed when they time out. If you
assign a handler on the request, the response, or the server's
'timeout'
events, then it is your responsibility to handle timed out
sockets.
Returns response
.
response.statusCode#
When using implicit headers (not calling response.writeHead()
explicitly),
this property controls the status code that will be sent to the client when
the headers get flushed.
Example:
response.statusCode = 404;
After response header was sent to the client, this property indicates the status code which was sent out.
response.statusMessage#
When using implicit headers (not calling response.writeHead()
explicitly), this property
controls the status message that will be sent to the client when the headers get
flushed. If this is left as undefined
then the standard message for the status
code will be used.
Example:
response.statusMessage = 'Not found';
After response header was sent to the client, this property indicates the status message which was sent out.
response.write(chunk[, encoding][, callback])#
chunk
<string> | <Buffer>encoding
<string>callback
<Function>- Returns: <Boolean>
If this method is called and response.writeHead()
has not been called,
it will switch to implicit header mode and flush the implicit headers.
This sends a chunk of the response body. This method may be called multiple times to provide successive parts of the body.
Note that in the http
module, the response body is omitted when the
request is a HEAD request. Similarly, the 204
and 304
responses
must not include a message body.
chunk
can be a string or a buffer. If chunk
is a string,
the second parameter specifies how to encode it into a byte stream.
By default the encoding
is 'utf8'
. callback
will be called when this chunk
of data is flushed.
Note: This is the raw HTTP body and has nothing to do with higher-level multi-part body encodings that may be used.
The first time response.write()
is called, it will send the buffered
header information and the first body to the client. The second time
response.write()
is called, Node.js assumes you're going to be streaming
data, and sends that separately. That is, the response is buffered up to the
first chunk of body.
Returns true
if the entire data was flushed successfully to the kernel
buffer. Returns false
if all or part of the data was queued in user memory.
'drain'
will be emitted when the buffer is free again.
response.writeContinue()#
Sends a HTTP/1.1 100 Continue message to the client, indicating that
the request body should be sent. See the 'checkContinue'
event on Server
.
response.writeHead(statusCode[, statusMessage][, headers])#
Sends a response header to the request. The status code is a 3-digit HTTP
status code, like 404
. The last argument, headers
, are the response headers.
Optionally one can give a human-readable statusMessage
as the second
argument.
Example:
const body = 'hello world';
response.writeHead(200, {
'Content-Length': Buffer.byteLength(body),
'Content-Type': 'text/plain' });
This method must only be called once on a message and it must
be called before response.end()
is called.
If you call response.write()
or response.end()
before calling this,
the implicit/mutable headers will be calculated and call this function for you.
When headers have been set with response.setHeader()
, they will be merged with
any headers passed to response.writeHead()
, with the headers passed to
response.writeHead()
given precedence.
// returns content-type = text/plain
const server = http.createServer((req, res) => {
res.setHeader('Content-Type', 'text/html');
res.setHeader('X-Foo', 'bar');
res.writeHead(200, {'Content-Type': 'text/plain'});
res.end('ok');
});
Note that Content-Length is given in bytes not characters. The above example
works because the string 'hello world'
contains only single byte characters.
If the body contains higher coded characters then Buffer.byteLength()
should be used to determine the number of bytes in a given encoding.
And Node.js does not check whether Content-Length and the length of the body
which has been transmitted are equal or not.
Attempting to set a header field name or value that contains invalid characters
will result in a TypeError
being thrown.
Class: http.IncomingMessage#
An IncomingMessage
object is created by http.Server
or
http.ClientRequest
and passed as the first argument to the 'request'
and 'response'
event respectively. It may be used to access response status,
headers and data.
It implements the Readable Stream interface, as well as the following additional events, methods, and properties.
Event: 'aborted'#
Emitted when the request has been aborted and the network socket has closed.
Event: 'close'#
Indicates that the underlying connection was closed.
Just like 'end'
, this event occurs only once per response.
message.destroy([error])#
error
<Error>
Calls destroy()
on the socket that received the IncomingMessage
. If error
is provided, an 'error'
event is emitted and error
is passed as an argument
to any listeners on the event.
message.headers#
The request/response headers object.
Key-value pairs of header names and values. Header names are lower-cased. Example:
// Prints something like:
//
// { 'user-agent': 'curl/7.22.0',
// host: '127.0.0.1:8000',
// accept: '*/*' }
console.log(request.headers);
Duplicates in raw headers are handled in the following ways, depending on the header name:
- Duplicates of
age
,authorization
,content-length
,content-type
,etag
,expires
,from
,host
,if-modified-since
,if-unmodified-since
,last-modified
,location
,max-forwards
,proxy-authorization
,referer
,retry-after
, oruser-agent
are discarded. set-cookie
is always an array. Duplicates are added to the array.- For all other headers, the values are joined together with ', '.
message.httpVersion#
In case of server request, the HTTP version sent by the client. In the case of
client response, the HTTP version of the connected-to server.
Probably either '1.1'
or '1.0'
.
Also message.httpVersionMajor
is the first integer and
message.httpVersionMinor
is the second.
message.method#
Only valid for request obtained from http.Server
.
The request method as a string. Read only. Example:
'GET'
, 'DELETE'
.
message.rawHeaders#
The raw request/response headers list exactly as they were received.
Note that the keys and values are in the same list. It is not a list of tuples. So, the even-numbered offsets are key values, and the odd-numbered offsets are the associated values.
Header names are not lowercased, and duplicates are not merged.
// Prints something like:
//
// [ 'user-agent',
// 'this is invalid because there can be only one',
// 'User-Agent',
// 'curl/7.22.0',
// 'Host',
// '127.0.0.1:8000',
// 'ACCEPT',
// '*/*' ]
console.log(request.rawHeaders);
message.rawTrailers#
The raw request/response trailer keys and values exactly as they were
received. Only populated at the 'end'
event.
message.setTimeout(msecs, callback)#
msecs
<number>callback
<Function>
Calls message.connection.setTimeout(msecs, callback)
.
Returns message
.
message.statusCode#
Only valid for response obtained from http.ClientRequest
.
The 3-digit HTTP response status code. E.G. 404
.
message.statusMessage#
Only valid for response obtained from http.ClientRequest
.
The HTTP response status message (reason phrase). E.G. OK
or Internal Server Error
.
message.socket#
The net.Socket
object associated with the connection.
With HTTPS support, use request.socket.getPeerCertificate()
to obtain the
client's authentication details.
message.trailers#
The request/response trailers object. Only populated at the 'end'
event.
message.url#
Only valid for request obtained from http.Server
.
Request URL string. This contains only the URL that is present in the actual HTTP request. If the request is:
GET /status?name=ryan HTTP/1.1\r\n
Accept: text/plain\r\n
\r\n
Then request.url
will be:
'/status?name=ryan'
If you would like to parse the URL into its parts, you can use
require('url').parse(request.url)
. Example:
$ node
> require('url').parse('/status?name=ryan')
{
href: '/status?name=ryan',
search: '?name=ryan',
query: 'name=ryan',
pathname: '/status'
}
If you would like to extract the parameters from the query string,
you can use the require('querystring').parse
function, or pass
true
as the second argument to require('url').parse
. Example:
$ node
> require('url').parse('/status?name=ryan', true)
{
href: '/status?name=ryan',
search: '?name=ryan',
query: {name: 'ryan'},
pathname: '/status'
}
http.METHODS#
A list of the HTTP methods that are supported by the parser.
http.STATUS_CODES#
A collection of all the standard HTTP response status codes, and the
short description of each. For example, http.STATUS_CODES[404] === 'Not
Found'
.
http.createClient([port][, host])#
http.request()
instead.Constructs a new HTTP client. port
and host
refer to the server to be
connected to.
http.createServer([requestListener])#
- Returns: <http.Server>
Returns a new instance of http.Server
.
The requestListener
is a function which is automatically
added to the 'request'
event.
http.get(options[, callback])#
options
<Object>callback
<Function>- Returns: <http.ClientRequest>
Since most requests are GET requests without bodies, Node.js provides this
convenience method. The only difference between this method and
http.request()
is that it sets the method to GET and calls req.end()
automatically. Note that the callback must take care to consume the response
data for reasons stated in http.ClientRequest
section.
The callback
is invoked with a single argument that is an instance of
http.IncomingMessage
JSON Fetching Example:
http.get('http://nodejs.org/dist/index.json', (res) => {
const statusCode = res.statusCode;
const contentType = res.headers['content-type'];
let error;
if (statusCode !== 200) {
error = new Error('Request Failed.\n' +
`Status Code: ${statusCode}`);
} else if (!/^application\/json/.test(contentType)) {
error = new Error('Invalid content-type.\n' +
`Expected application/json but received ${contentType}`);
}
if (error) {
console.log(error.message);
// consume response data to free up memory
res.resume();
return;
}
res.setEncoding('utf8');
let rawData = '';
res.on('data', (chunk) => rawData += chunk);
res.on('end', () => {
try {
const parsedData = JSON.parse(rawData);
console.log(parsedData);
} catch (e) {
console.log(e.message);
}
});
}).on('error', (e) => {
console.log(`Got error: ${e.message}`);
});
http.globalAgent#
Global instance of Agent
which is used as the default for all HTTP client
requests.
http.request(options[, callback])#
options
<Object>protocol
<string> Protocol to use. Defaults to'http:'
.host
<string> A domain name or IP address of the server to issue the request to. Defaults to'localhost'
.hostname
<string> Alias forhost
. To supporturl.parse()
,hostname
is preferred overhost
.family
<number> IP address family to use when resolvinghost
andhostname
. Valid values are4
or6
. When unspecified, both IP v4 and v6 will be used.port
<number> Port of remote server. Defaults to 80.localAddress
<string> Local interface to bind for network connections.socketPath
<string> Unix Domain Socket (use one of host:port or socketPath).method
<string> A string specifying the HTTP request method. Defaults to'GET'
.path
<string> Request path. Defaults to'/'
. Should include query string if any. E.G.'/index.html?page=12'
. An exception is thrown when the request path contains illegal characters. Currently, only spaces are rejected but that may change in the future.headers
<Object> An object containing request headers.auth
<string> Basic authentication i.e.'user:password'
to compute an Authorization header.agent
<http.Agent> | <boolean> ControlsAgent
behavior. Possible values:undefined
(default): usehttp.globalAgent
for this host and port.Agent
object: explicitly use the passed inAgent
.false
: causes a newAgent
with default values to be used.
createConnection
<Function> A function that produces a socket/stream to use for the request when theagent
option is not used. This can be used to avoid creating a customAgent
class just to override the defaultcreateConnection
function. Seeagent.createConnection()
for more details.timeout
<Integer>: A number specifying the socket timeout in milliseconds. This will set the timeout before the socket is connected.
callback
<Function>- Returns: <http.ClientRequest>
Node.js maintains several connections per server to make HTTP requests. This function allows one to transparently issue requests.
options
can be an object or a string. If options
is a string, it is
automatically parsed with url.parse()
.
The optional callback
parameter will be added as a one-time listener for
the 'response'
event.
http.request()
returns an instance of the http.ClientRequest
class. The ClientRequest
instance is a writable stream. If one needs to
upload a file with a POST request, then write to the ClientRequest
object.
Example:
const postData = querystring.stringify({
'msg': 'Hello World!'
});
const options = {
hostname: 'www.google.com',
port: 80,
path: '/upload',
method: 'POST',
headers: {
'Content-Type': 'application/x-www-form-urlencoded',
'Content-Length': Buffer.byteLength(postData)
}
};
const req = http.request(options, (res) => {
console.log(`STATUS: ${res.statusCode}`);
console.log(`HEADERS: ${JSON.stringify(res.headers)}`);
res.setEncoding('utf8');
res.on('data', (chunk) => {
console.log(`BODY: ${chunk}`);
});
res.on('end', () => {
console.log('No more data in response.');
});
});
req.on('error', (e) => {
console.log(`problem with request: ${e.message}`);
});
// write data to request body
req.write(postData);
req.end();
Note that in the example req.end()
was called. With http.request()
one
must always call req.end()
to signify that you're done with the request -
even if there is no data being written to the request body.
If any error is encountered during the request (be that with DNS resolution,
TCP level errors, or actual HTTP parse errors) an 'error'
event is emitted
on the returned request object. As with all 'error'
events, if no listeners
are registered the error will be thrown.
There are a few special headers that should be noted.
Sending a 'Connection: keep-alive' will notify Node.js that the connection to the server should be persisted until the next request.
Sending a 'Content-Length' header will disable the default chunked encoding.
Sending an 'Expect' header will immediately send the request headers. Usually, when sending 'Expect: 100-continue', you should both set a timeout and listen for the
'continue'
event. See RFC2616 Section 8.2.3 for more information.Sending an Authorization header will override using the
auth
option to compute basic authentication.
HTTPS#
HTTPS is the HTTP protocol over TLS/SSL. In Node.js this is implemented as a separate module.
Class: https.Agent#
An Agent object for HTTPS similar to http.Agent
. See https.request()
for more information.
Class: https.Server#
This class is a subclass of tls.Server
and emits events same as
http.Server
. See http.Server
for more information.
server.setTimeout([msecs][, callback])#
msecs
<number> Defaults to 120000 (2 minutes).callback
<Function>
server.timeout([msecs])#
msecs
<number> Defaults to 120000 (2 minutes).
See http.Server#timeout
.
https.createServer(options[, requestListener])#
options
<Object> Acceptsoptions
fromtls.createServer()
andtls.createSecureContext()
.requestListener
<Function> A listener to be added to therequest
event.
Example:
// curl -k https://localhost:8000/
const https = require('https');
const fs = require('fs');
const options = {
key: fs.readFileSync('test/fixtures/keys/agent2-key.pem'),
cert: fs.readFileSync('test/fixtures/keys/agent2-cert.pem')
};
https.createServer(options, (req, res) => {
res.writeHead(200);
res.end('hello world\n');
}).listen(8000);
Or
const https = require('https');
const fs = require('fs');
const options = {
pfx: fs.readFileSync('test/fixtures/test_cert.pfx'),
passphrase: 'sample'
};
https.createServer(options, (req, res) => {
res.writeHead(200);
res.end('hello world\n');
}).listen(8000);
server.close([callback])#
callback
<Function>
See http.close()
for details.
server.listen(handle[, callback])#
handle
<Object>callback
<Function>
server.listen(path[, callback])#
path
<string>callback
<Function>
server.listen([port][, host][, backlog][, callback])#
port
<number>hostname
<string>backlog
<number>callback
<Function>
See http.listen()
for details.
https.get(options[, callback])#
options
<Object> | <string> Accepts the sameoptions
ashttps.request()
, with themethod
always set toGET
.callback
<Function>
Like http.get()
but for HTTPS.
options
can be an object or a string. If options
is a string, it is
automatically parsed with url.parse()
.
Example:
const https = require('https');
https.get('https://encrypted.google.com/', (res) => {
console.log('statusCode:', res.statusCode);
console.log('headers:', res.headers);
res.on('data', (d) => {
process.stdout.write(d);
});
}).on('error', (e) => {
console.error(e);
});
https.globalAgent#
Global instance of https.Agent
for all HTTPS client requests.
https.request(options[, callback])#
options
<Object> | <string> Accepts alloptions
fromhttp.request()
, with some differences in default values:protocol
Defaults tohttps:
port
Defaults to443
.agent
Defaults tohttps.globalAgent
.
callback
<Function>
Makes a request to a secure web server.
The following additional options
from tls.connect()
are also accepted when using a
custom Agent
:
pfx
, key
, passphrase
, cert
, ca
, ciphers
, rejectUnauthorized
, secureProtocol
, servername
options
can be an object or a string. If options
is a string, it is
automatically parsed with url.parse()
.
Example:
const https = require('https');
const options = {
hostname: 'encrypted.google.com',
port: 443,
path: '/',
method: 'GET'
};
const req = https.request(options, (res) => {
console.log('statusCode:', res.statusCode);
console.log('headers:', res.headers);
res.on('data', (d) => {
process.stdout.write(d);
});
});
req.on('error', (e) => {
console.error(e);
});
req.end();
Example using options from tls.connect()
:
const options = {
hostname: 'encrypted.google.com',
port: 443,
path: '/',
method: 'GET',
key: fs.readFileSync('test/fixtures/keys/agent2-key.pem'),
cert: fs.readFileSync('test/fixtures/keys/agent2-cert.pem')
};
options.agent = new https.Agent(options);
const req = https.request(options, (res) => {
// ...
});
Alternatively, opt out of connection pooling by not using an Agent
.
Example:
const options = {
hostname: 'encrypted.google.com',
port: 443,
path: '/',
method: 'GET',
key: fs.readFileSync('test/fixtures/keys/agent2-key.pem'),
cert: fs.readFileSync('test/fixtures/keys/agent2-cert.pem'),
agent: false
};
const req = https.request(options, (res) => {
// ...
});
Internationalization Support#
Node.js has many features that make it easier to write internationalized programs. Some of them are:
- Locale-sensitive or Unicode-aware functions in the ECMAScript Language Specification:
- All functionality described in the ECMAScript Internationalization API
Specification (aka ECMA-402):
Intl
object- Locale-sensitive methods like
String.prototype.localeCompare()
andDate.prototype.toLocaleString()
Node.js (and its underlying V8 engine) uses ICU to implement these features in native C/C++ code. However, some of them require a very large ICU data file in order to support all locales of the world. Because it is expected that most Node.js users will make use of only a small portion of ICU functionality, only a subset of the full ICU data set is provided by Node.js by default. Several options are provided for customizing and expanding the ICU data set either when building or running Node.js.
Options for building Node.js#
To control how ICU is used in Node.js, four configure
options are available
during compilation. Additional details on how to compile Node.js are documented
in BUILDING.md.
--with-intl=none
/--without-intl
--with-intl=system-icu
--with-intl=small-icu
(default)--with-intl=full-icu
An overview of available Node.js and JavaScript features for each configure
option:
none |
system-icu |
small-icu |
full-icu |
|
---|---|---|---|---|
String.prototype.normalize() |
none (function is no-op) | full | full | full |
String.prototype.to*Case() |
full | full | full | full |
Intl |
none (object does not exist) | partial/full (depends on OS) | partial (English-only) | full |
String.prototype.localeCompare() |
partial (not locale-aware) | full | full | full |
String.prototype.toLocale*Case() |
partial (not locale-aware) | full | full | full |
Number.prototype.toLocaleString() |
partial (not locale-aware) | partial/full (depends on OS) | partial (English-only) | full |
Date.prototype.toLocale*String() |
partial (not locale-aware) | partial/full (depends on OS) | partial (English-only) | full |
Note: The "(not locale-aware)" designation denotes that the function carries
out its operation just like the non-Locale
version of the function, if one
exists. For example, under none
mode, Date.prototype.toLocaleString()
's
operation is identical to that of Date.prototype.toString()
.
Disable all internationalization features (none
)#
If this option is chosen, most internationalization features mentioned above
will be unavailable in the resulting node
binary.
Build with a pre-installed ICU (system-icu
)#
Node.js can link against an ICU build already installed on the system. In fact, most Linux distributions already come with ICU installed, and this option would make it possible to reuse the same set of data used by other components in the OS.
Functionalities that only require the ICU library itself, such as
String.prototype.normalize()
, are fully supported under system-icu
.
Features that require ICU locale data in addition, such as
Intl.DateTimeFormat
may be fully or partially supported, depending on
the completeness of the ICU data installed on the system.
Embed a limited set of ICU data (small-icu
)#
This option makes the resulting binary link against the ICU library statically,
and includes a subset of ICU data (typically only the English locale) within
the node
executable.
Functionalities that only require the ICU library itself, such as
String.prototype.normalize()
, are fully supported under small-icu
.
Features that require ICU locale data in addition, such as
Intl.DateTimeFormat
, generally only work with the English locale:
const january = new Date(9e8);
const english = new Intl.DateTimeFormat('en', { month: 'long' });
const spanish = new Intl.DateTimeFormat('es', { month: 'long' });
console.log(english.format(january));
// Prints "January"
console.log(spanish.format(january));
// Prints "January" or "M01" on small-icu
// Should print "enero"
This mode provides a good balance between features and binary size, and it is
the default behavior if no --with-intl
flag is passed. The official binaries
are also built in this mode.
Providing ICU data at runtime#
If the small-icu
option is used, one can still provide additional locale data
at runtime so that the JS methods would work for all ICU locales. Assuming the
data file is stored at /some/directory
, it can be made available to ICU
through either:
The
NODE_ICU_DATA
environment variable:env NODE_ICU_DATA=/some/directory node
The
--icu-data-dir
CLI parameter:node --icu-data-dir=/some/directory
(If both are specified, the --icu-data-dir
CLI parameter takes precedence.)
ICU is able to automatically find and load a variety of data formats, but the
data must be appropriate for the ICU version, and the file correctly named.
The most common name for the data file is icudt5X[bl].dat
, where 5X
denotes
the intended ICU version, and b
or l
indicates the system's endianness.
Check "ICU Data" article in the ICU User Guide for other supported formats
and more details on ICU data in general.
The full-icu npm module can greatly simplify ICU data installation by
detecting the ICU version of the running node
executable and downloading the
appropriate data file. After installing the module through npm i full-icu
,
the data file will be available at ./node_modules/full-icu
. This path can be
then passed either to NODE_ICU_DATA
or --icu-data-dir
as shown above to
enable full Intl
support.
Embed the entire ICU (full-icu
)#
This option makes the resulting binary link against ICU statically and include a full set of ICU data. A binary created this way has no further external dependencies and supports all locales, but might be rather large. See BUILDING.md on how to compile a binary using this mode.
Detecting internationalization support#
To verify that ICU is enabled at all (system-icu
, small-icu
, or
full-icu
), simply checking the existence of Intl
should suffice:
const hasICU = typeof Intl === 'object';
Alternatively, checking for process.versions.icu
, a property defined only
when ICU is enabled, works too:
const hasICU = typeof process.versions.icu === 'string';
To check for support for a non-English locale (i.e. full-icu
or
system-icu
), Intl.DateTimeFormat
can be a good distinguishing factor:
const hasFullICU = (() => {
try {
const january = new Date(9e8);
const spanish = new Intl.DateTimeFormat('es', { month: 'long' });
return spanish.format(january) === 'enero';
} catch (err) {
return false;
}
})();
For more verbose tests for Intl
support, the following resources may be found
to be helpful:
- btest402: Generally used to check whether Node.js with
Intl
support is built correctly. - Test262: ECMAScript's official conformance test suite includes a section dedicated to ECMA-402.
Modules#
In the Node.js module system, each file is treated as a separate module. For
example, consider a file named foo.js
:
const circle = require('./circle.js');
console.log(`The area of a circle of radius 4 is ${circle.area(4)}`);
On the first line, foo.js
loads the module circle.js
that is in the same
directory as foo.js
.
Here are the contents of circle.js
:
const { PI } = Math;
exports.area = (r) => PI * r * r;
exports.circumference = (r) => 2 * PI * r;
The module circle.js
has exported the functions area()
and
circumference()
. To add functions and objects to the root of your module,
you can add them to the special exports
object.
Variables local to the module will be private, because the module is wrapped
in a function by Node.js (see module wrapper).
In this example, the variable PI
is private to circle.js
.
If you want the root of your module's export to be a function (such as a
constructor) or if you want to export a complete object in one assignment
instead of building it one property at a time, assign it to module.exports
instead of exports
.
Below, bar.js
makes use of the square
module, which exports a constructor:
const Square = require('./square.js');
const mySquare = new Square(2);
console.log(`The area of mySquare is ${mySquare.area()}`);
The square
module is defined in square.js
:
// assigning to exports will not modify module, must use module.exports
module.exports = (width) => {
return {
area: () => width * width
};
};
The module system is implemented in the require('module')
module.
Accessing the main module#
When a file is run directly from Node.js, require.main
is set to its
module
. That means that you can determine whether a file has been run
directly by testing require.main === module
.
For a file foo.js
, this will be true
if run via node foo.js
, but
false
if run by require('./foo')
.
Because module
provides a filename
property (normally equivalent to
__filename
), the entry point of the current application can be obtained
by checking require.main.filename
.
Addenda: Package Manager Tips#
The semantics of Node.js's require()
function were designed to be general
enough to support a number of reasonable directory structures. Package manager
programs such as dpkg
, rpm
, and npm
will hopefully find it possible to
build native packages from Node.js modules without modification.
Below we give a suggested directory structure that could work:
Let's say that we wanted to have the folder at
/usr/lib/node/<some-package>/<some-version>
hold the contents of a
specific version of a package.
Packages can depend on one another. In order to install package foo
, you
may have to install a specific version of package bar
. The bar
package
may itself have dependencies, and in some cases, these dependencies may even
collide or form cycles.
Since Node.js looks up the realpath
of any modules it loads (that is,
resolves symlinks), and then looks for their dependencies in the node_modules
folders as described here, this
situation is very simple to resolve with the following architecture:
/usr/lib/node/foo/1.2.3/
- Contents of thefoo
package, version 1.2.3./usr/lib/node/bar/4.3.2/
- Contents of thebar
package thatfoo
depends on./usr/lib/node/foo/1.2.3/node_modules/bar
- Symbolic link to/usr/lib/node/bar/4.3.2/
./usr/lib/node/bar/4.3.2/node_modules/*
- Symbolic links to the packages thatbar
depends on.
Thus, even if a cycle is encountered, or if there are dependency conflicts, every module will be able to get a version of its dependency that it can use.
When the code in the foo
package does require('bar')
, it will get the
version that is symlinked into /usr/lib/node/foo/1.2.3/node_modules/bar
.
Then, when the code in the bar
package calls require('quux')
, it'll get
the version that is symlinked into
/usr/lib/node/bar/4.3.2/node_modules/quux
.
Furthermore, to make the module lookup process even more optimal, rather
than putting packages directly in /usr/lib/node
, we could put them in
/usr/lib/node_modules/<name>/<version>
. Then Node.js will not bother
looking for missing dependencies in /usr/node_modules
or /node_modules
.
In order to make modules available to the Node.js REPL, it might be useful to
also add the /usr/lib/node_modules
folder to the $NODE_PATH
environment
variable. Since the module lookups using node_modules
folders are all
relative, and based on the real path of the files making the calls to
require()
, the packages themselves can be anywhere.
All Together...#
To get the exact filename that will be loaded when require()
is called, use
the require.resolve()
function.
Putting together all of the above, here is the high-level algorithm
in pseudocode of what require.resolve()
does:
require(X) from module at path Y
1. If X is a core module,
a. return the core module
b. STOP
2. If X begins with '/'
a. set Y to be the filesystem root
3. If X begins with './' or '/' or '../'
a. LOAD_AS_FILE(Y + X)
b. LOAD_AS_DIRECTORY(Y + X)
4. LOAD_NODE_MODULES(X, dirname(Y))
5. THROW "not found"
LOAD_AS_FILE(X)
1. If X is a file, load X as JavaScript text. STOP
2. If X.js is a file, load X.js as JavaScript text. STOP
3. If X.json is a file, parse X.json to a JavaScript Object. STOP
4. If X.node is a file, load X.node as binary addon. STOP
LOAD_INDEX(X)
1. If X/index.js is a file, load X/index.js as JavaScript text. STOP
2. If X/index.json is a file, parse X/index.json to a JavaScript object. STOP
3. If X/index.node is a file, load X/index.node as binary addon. STOP
LOAD_AS_DIRECTORY(X)
1. If X/package.json is a file,
a. Parse X/package.json, and look for "main" field.
b. let M = X + (json main field)
c. LOAD_AS_FILE(M)
d. LOAD_INDEX(M)
2. LOAD_INDEX(X)
LOAD_NODE_MODULES(X, START)
1. let DIRS=NODE_MODULES_PATHS(START)
2. for each DIR in DIRS:
a. LOAD_AS_FILE(DIR/X)
b. LOAD_AS_DIRECTORY(DIR/X)
NODE_MODULES_PATHS(START)
1. let PARTS = path split(START)
2. let I = count of PARTS - 1
3. let DIRS = []
4. while I >= 0,
a. if PARTS[I] = "node_modules" CONTINUE
b. DIR = path join(PARTS[0 .. I] + "node_modules")
c. DIRS = DIRS + DIR
d. let I = I - 1
5. return DIRS
Caching#
Modules are cached after the first time they are loaded. This means
(among other things) that every call to require('foo')
will get
exactly the same object returned, if it would resolve to the same file.
Multiple calls to require('foo')
may not cause the module code to be
executed multiple times. This is an important feature. With it,
"partially done" objects can be returned, thus allowing transitive
dependencies to be loaded even when they would cause cycles.
If you want to have a module execute code multiple times, then export a function, and call that function.
Module Caching Caveats#
Modules are cached based on their resolved filename. Since modules may
resolve to a different filename based on the location of the calling
module (loading from node_modules
folders), it is not a guarantee
that require('foo')
will always return the exact same object, if it
would resolve to different files.
Additionally, on case-insensitive file systems or operating systems, different
resolved filenames can point to the same file, but the cache will still treat
them as different modules and will reload the file multiple times. For example,
require('./foo')
and require('./FOO')
return two different objects,
irrespective of whether or not ./foo
and ./FOO
are the same file.
Core Modules#
Node.js has several modules compiled into the binary. These modules are described in greater detail elsewhere in this documentation.
The core modules are defined within Node.js's source and are located in the
lib/
folder.
Core modules are always preferentially loaded if their identifier is
passed to require()
. For instance, require('http')
will always
return the built in HTTP module, even if there is a file by that name.
Cycles#
When there are circular require()
calls, a module might not have finished
executing when it is returned.
Consider this situation:
a.js
:
console.log('a starting');
exports.done = false;
const b = require('./b.js');
console.log('in a, b.done = %j', b.done);
exports.done = true;
console.log('a done');
b.js
:
console.log('b starting');
exports.done = false;
const a = require('./a.js');
console.log('in b, a.done = %j', a.done);
exports.done = true;
console.log('b done');
main.js
:
console.log('main starting');
const a = require('./a.js');
const b = require('./b.js');
console.log('in main, a.done=%j, b.done=%j', a.done, b.done);
When main.js
loads a.js
, then a.js
in turn loads b.js
. At that
point, b.js
tries to load a.js
. In order to prevent an infinite
loop, an unfinished copy of the a.js
exports object is returned to the
b.js
module. b.js
then finishes loading, and its exports
object is
provided to the a.js
module.
By the time main.js
has loaded both modules, they're both finished.
The output of this program would thus be:
$ node main.js
main starting
a starting
b starting
in b, a.done = false
b done
in a, b.done = true
a done
in main, a.done=true, b.done=true
If you have cyclic module dependencies in your program, make sure to plan accordingly.