node - evented I/O for V8 javascript


An example of a web server written with Node which responds with "Hello World":

var sys = require("sys"),
   http = require("http");
http.createServer(function (request, response) {
  response.sendHeader(200, {"Content-Type": "text/plain"});
  response.sendBody("Hello World\n");
sys.puts("Server running at");

To run the server, put the code into a file called example.js and execute it with the node program

> node example.js
Server running at


Node supports 3 string encodings. UTF-8 ("utf8"), ASCII ("ascii"), and Binary ("binary"). "ascii" and "binary" only look at the first 8 bits of the 16bit javascript string characters. Both are relatively fast—use them if you can. "utf8" is slower and should be avoided when possible.

Unless otherwise noted, functions are all asynchronous and do not block execution.

Global Objects


The global namespace object.


The process object. Most stuff lives in here. See the "process object" section.


See the modules section.


The search path for absolute path arguments to require().


The filename of the script being executed.


A reference to the current module (of type process.Module). In particular module.exports is the same as the exports object. See src/process.js for more information.

The process Object

Event Parameters Notes



Made when the process exits. A listener on this event should not try to perform I/O since the process will forcibly exit in less than microsecond. However, it is a good hook to perform constant time checks of the module’s state (like for unit tests).
The parameter code is the integer exit code passed to process.exit().



Emitted when the processes receives a signal. See sigaction(2) for a list of standard POSIX signal names such as SIGINT, SIGUSR1, etc.


An array containing the command line arguments.


An object containing the user environment. See environ(7).

The PID of the process.


What platform you’re running on. "linux2", "darwin", etc.


Returns the memory usage of the Node process: e.g. {"rss":5828608,"vsize":3112529920}


Ends the process with the specified code. By default it exits with the success code 0.


Returns the current working directory of the process.

process.kill(pid, signal="SIGTERM")

Send a signal to a process. pid is the process id and signal is the signal to send; for example, "SIGINT" or "SIGUSR1". See kill(2) for more information.

process.compile(source, scriptOrigin)

Just like eval() except that you can specify a scriptOrigin for better error reporting.

process.mixin([deep], target, object1, [objectN])

Extend one object with one or more others, returning the modified object. If no target is specified, the GLOBAL namespace itself is extended. Keep in mind that the target object will be modified, and will be returned from process.mixin().

If a boolean true is specified as the first argument, Node performs a deep copy, recursively copying any objects it finds. Otherwise, the copy will share structure with the original object(s).

Undefined properties are not copied. However, properties inherited from the object’s prototype will be copied over.

System module

These function are in the module "sys". Use require("sys") to access them.


Outputs the string and a trailing new-line to stdout.


Like puts() but without the trailing new-line.


A synchronous output function. Will block the process and output the string immediately to stdout.


Return a string representation of the object. (For debugging.)


Executes the command as a child process, buffers the output and returns it in a promise callback.

var sys = require("sys");
sys.exec("ls /").addCallback(function (stdout, stderr) {
  • on success: stdout buffer, stderr buffer

  • on error: exit code, stdout buffer, stderr buffer


Many objects in Node emit events: a TCP server emits an event each time there is a connection, a child process emits an event when it exits. All objects which emit events are are instances of process.EventEmitter.

Events are represented by a camel-cased string. Here are some examples: "connection", "receive", "messageBegin".

Functions can be then be attached to objects, to be executed when an event is emitted. These functions are called listeners.

Some asynchronous file operations return an EventEmitter called a promise. A promise emits just a single event when the operation is complete.


All EventEmitters emit the event "newListener" when new listeners are added.

Event Parameters Notes


event, listener

This event is made any time someone adds a new listener.

emitter.addListener(event, listener)

Adds a listener to the end of the listeners array for the specified event.

server.addListener("connection", function (socket) {
  puts("someone connected!");

Returns an array of listeners for the specified event. This array can be manipulated, e.g. to remove listeners.

emitter.emit(event, arg1, arg2, …)

Execute each of the listeners in order with the supplied arguments.


process.Promise inherits from process.eventEmitter. A promise emits one of two events: "success" or "error". After emitting its event, it will not emit anymore events.

Event Parameters Notes








Adds a listener for the "success" event. Returns the same promise object.


Adds a listener for the "error" event. Returns the same promise object.


Adds a listener for the "cancel" event. Returns the same promise object.

promise.emitSuccess(arg1, arg2, …)

If you created the promise (by doing new process.Promise()) then call emitSuccess to emit the "success" event with the given arguments.

(promise.emit("success", arg1, arg2, …) should also work, but doesn’t at the moment due to a bug; use emitSuccess instead.)

promise.emitError(arg1, arg2, …)

Emits the "error" event.

promise.emitCancel(arg1, arg2, …)

Emits the "cancel" event. You may still get a "success" or "error" callback if the promise giver does not handle the cancel event. Use promise.cancel() to ignore any later events.


Clears all "success" and "error" event listeners from the promise, then emits the "cancel" event. Whether or not the promise is actually canceled or not depends on the promise giver. This also clears Promise.timeout() if one was set.

promise.timeout(timeout = undefined)

If the timeout parameter is provided, the promise will emit an "error" event after the given amount of millseconds. The timeout is canceled by any "success", "error" or "cancel" event being emitted by the Promise.

To tell apart a timeout from a regular "error" event, use the following test:

promise.addErrback(function(e) {
  if (e instanceof Error && e.message === "timeout") {
    // handle timeout
  } else {
    // handle regular error

If the timeout parameter is not provided, the current timeout value, if any, is returned.


Blocks futher execution until the promise emits a success or error event. Events setup before the call to promise.wait() was made may still be emitted and executed while promise.wait() is blocking.

If there was a single argument to the "success" event then it is returned. If there were multiple arguments to "success" then they are returned as an array.

If "error" was emitted instead, wait() throws an error.

IMPORTANT promise.wait() is not a true fiber/coroutine. If any other promises are created and made to wait while the first promise waits, the first promise’s wait will not return until all others return. The benefit of this is a simple implementation and the event loop does not get blocked. Disadvantage is the possibility of situations where the promise stack grows infinitely large because promises keep getting created and keep being told to wait(). Use promise.wait() sparingly—probably best used only during program setup, not during busy server activity.

Standard I/O

Standard I/O is handled through a special object process.stdio. stdout and stdin are fully non-blocking (even when piping to files). stderr is synchronous.

Event Parameters Notes



Made when stdin has received a chunk of data. Depending on the encoding that stdin was opened with, data will be a string. This event will only be emited after has been called.


Made when stdin has been closed."utf8")

Open stdin. The program will not exit until process.stdio.close() has been called or the "close" event has been emitted.


Write data to stdout.


Write data to stderr. Synchronous.


Close stdin.


Node uses the CommonJS module system

Node has a simple module loading system. In Node, files and modules are in one-to-one correspondence. As an example, foo.js loads the module circle.js in the same directory.

The contents of foo.js:

var circle = require("./circle"),
var sys = require("sys");
sys.puts("The area of a circle of radius 4 is " + circle.area(4));

The contents of circle.js:

var PI = 3.14;

exports.area = function (r) {
  return PI * r * r;

exports.circumference = function (r) {
  return 2 * PI * r;

The module circle.js has exported the functions area() and circumference(). To export an object, add to the special exports object. (Alternatively, one can use this instead of exports.) Variables local to the module will be private. In this example the variable PI is private to circle.js. The function puts() comes from the module "sys", which is a built-in module. Modules which are not prefixed by "./" are built-in module—more about this later.

A module prefixed with "./" is relative to the file calling require(). That is, circle.js must be in the same directory as foo.js for require("./circle") to find it.

Without the leading "./", like require("mjsunit") the module is searched for in the require.paths array. require.paths on my system looks like this:

[ "/home/ryan/.node_libraries"
, "/usr/local/lib/node/libraries"

That is, when require("mjsunit") is called Node looks for

  1. "/home/ryan/.node_libraries/mjsunit.js"

  2. "/home/ryan/.node_libraries/mjsunit.node"

  3. "/home/ryan/.node_libraries/mjsunit/index.js"

  4. "/home/ryan/.node_libraries/mjsunit/index.node"

  5. "/usr/local/lib/node/libraries/mjsunit.js"

  6. "/usr/local/lib/node/libraries/mjsunit.node"

  7. "/usr/local/lib/node/libraries/mjsunit/index.js"

  8. "/usr/local/lib/node/libraries/mjsunit/index.node"

interrupting once a file is found. Files ending in ".node" are binary Addon Modules; see the section below about addons. "index.js" allows one to package a module as a directory.

require.paths can be modified at runtime by simply unshifting new paths on to it and at startup with the NODE_PATH environmental variable (which should be a list of paths, colon separated).

Use process.mixin() to include modules into the global namespace.

process.mixin(GLOBAL, require("./circle"), require("sys"));
puts("The area of a cirlce of radius 4 is " + area(4));


setTimeout(callback, delay)

To schedule execution of callback after delay milliseconds. Returns a timeoutId for possible use with clearTimeout().


Prevents said timeout from triggering.

setInterval(callback, delay)

To schedule the repeated execution of callback every delay milliseconds. Returns a intervalId for possible use with clearInterval().


Stops a interval from triggering.

Child Processes

Node provides a tridirectional popen(3) facility through the class process.ChildProcess. It is possible to stream data through the child’s stdin, stdout, and stderr in a fully non-blocking way.


Event Parameters Notes



Each time the child process sends data to its stdout, this event is emitted. data is a string. + If the child process closes its stdout stream (a common thing to do on exit), this event will be emitted with data === null.



Identical to the "output" event except for stderr instead of stdout.



This event is emitted after the child process ends. code is the final exit code of the process. One can be assured that after this event is emitted that the "output" and "error" callbacks will no longer be made.

process.createChildProcess(command, args=[], env=ENV)

Launches a new process with the given command, command line arguments, and environmental variables. For example:

var ls = process.createChildProcess("ls", ["-lh", "/usr"]);
ls.addListener("output", function (data) {

Note, if you just want to buffer the output of a command and return it, then exec() in /sys.js might be better.

The PID of the child process.

child.write(data, encoding="ascii")

Write data to the child process’s stdin. The second argument is optional and specifies the encoding: possible values are "utf8", "ascii", and "binary".


Closes the process’s stdin stream.


Send a signal to the child process. If no argument is given, the process will be sent "SIGTERM". See signal(7) for a list of available signals.

POSIX module

File I/O is provided by simple wrappers around standard POSIX functions. To use this module do require("posix").

All POSIX wrappers have a similar form. They return a promise (process.Promise). Example of deleting a file:

var posix = require("posix"),
      sys = require("sys");

var promise = posix.unlink("/tmp/hello");

promise.addCallback(function () {
  sys.puts("successfully deleted /tmp/hello");

There is no guaranteed ordering to the POSIX wrappers. The following is very much prone to error

posix.rename("/tmp/hello", "/tmp/world");
posix.stat("/tmp/world").addCallback(function (stats) {
  sys.puts("stats: " + JSON.stringify(stats));

It could be that stat() is executed before the rename(). The correct way to do this is to chain the promises.

posix.rename("/tmp/hello", "/tmp/world").addCallback(function () {
  posix.stat("/tmp/world").addCallback(function (stats) {
    sys.puts("stats: " + JSON.stringify(stats));

Or use the promise.wait() functionality:

posix.rename("/tmp/hello", "/tmp/world").wait();
var stats = posix.stat("/tmp/world").wait();
sys.puts("stats: " + JSON.stringify(stats));
posix.rename(path1, path2)

See rename(2).

  • on success: no parameters.

  • on error: no parameters.


See stat(2).

  • on success: Returns posix.Stats object. It looks like this: { dev: 2049, ino: 305352, mode: 16877, nlink: 12, uid: 1000, gid: 1000, rdev: 0, size: 4096, blksize: 4096, blocks: 8, atime: "2009-06-29T11:11:55Z", mtime: "2009-06-29T11:11:40Z", ctime: "2009-06-29T11:11:40Z" } See the posix.Stats section below for more information.

  • on error: no parameters.


See unlink(2)

  • on success: no parameters.

  • on error: no parameters.


See rmdir(2)

  • on success: no parameters.

  • on error: no parameters.

posix.mkdir(path, mode)

See mkdir(2)

  • on success: no parameters.

  • on error: no parameters.


Reads the contents of a directory.

  • on success: One argument, an array containing the names (strings) of the files in the directory (excluding "." and "..").

  • on error: no parameters.


See close(2)

  • on success: no parameters.

  • on error: no parameters., flags, mode)

See open(2). The constants like O_CREAT are defined at process.O_CREAT.

  • on success: fd is given as the parameter.

  • on error: no parameters.

posix.write(fd, data, position, encoding)

Write data to the file specified by fd. position refers to the offset from the beginning of the file where this data should be written. If position is null, the data will be written at the current position. See pwrite(2).

  • on success: returns an integer written which specifies how many bytes were written.

  • on error: no parameters., length, position, encoding)

Read data from the file specified by fd.

length is an integer specifying the number of bytes to read.

position is an integer specifying where to begin reading from in the file.

  • on success: returns data, bytes_read, what was read from the file.

  • on error: no parameters., encoding="utf8")

Outputs the entire contents of a file. Example:"/etc/passwd").addCallback(function (content) {
  • on success: returns data, what was read from the file.

  • on error: no parameters.


Objects returned from posix.stat() are of this type.



To use the HTTP server and client one must require("http").

The HTTP interfaces in Node 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"
, "Accept": "*/*"

In order to support the full spectrum of possible HTTP applications, Node"s HTTP API is very low-level. It deals with connection handling and message parsing only. It parses a message into headers and body but it does not parse the actual headers or the body.


Event Parameters Notes


request, response

request is an instance of http.ServerRequest
response is an instance of http.ServerResponse



When a new TCP connection is established. connection is an object of type http.Connection. Usually users will not want to access this event. The connection can also be accessed at request.connection.



Emitted when the server closes. errorno is an integer which indicates what, if any, error caused the server to close. If no error occured errorno will be 0.

http.createServer(request_listener, options);

Returns a new web server object.

The options argument is optional. The options argument accepts the same values as the options argument for tcp.Server does.

The request_listener is a function which is automatically added to the "request" event.

server.listen(port, hostname)

Begin accepting connections on the specified port and hostname. If the hostname is omitted, the server will accept connections directed to any address. This function is synchronous.


Stops the server from accepting new connections.


This object is created internally by a HTTP server—not by the user—and passed as the first argument to a "request" listener.

Event Parameters Notes



Emitted when a piece of the message body is received. Example: A chunk of the body is given as the single argument. The transfer-encoding has been decoded. The body chunk is a String. The body encoding is set with request.setBodyEncoding().



Emitted exactly once for each message. No arguments. After emitted no other events will be emitted on the request.


The request method as a string. Read only. Example: "GET", "DELETE".


Request URI Object. This contains only the parameters that are present in the actual HTTP request. If the request is

GET /status?name=ryan HTTP/1.1\r\n
Accept: text/plain\r\n

Then request.uri will be

{ full: "/status?name=ryan",
  path: "/status",
  queryString: "name=ryan",
  params: { "name": "ryan" },
  fragment: ""

Read only.


The HTTP protocol version as a string. Read only. Examples: "1.1", "1.0"


Set the encoding for the request body. Either "utf8" or "binary". Defaults to "binary".


Pauses request from emitting events. Useful to throttle back an upload.


Resumes a paused request.


The http.Connection object.


This object is created internally by a HTTP server—not by the user. It is passed as the second parameter to the "request" event.

response.sendHeader(statusCode, headers)

Sends a response header to the request. The status code is a 3-digit HTTP status code, like 404. The second argument, headers are the response headers.


var body = "hello world";
response.sendHeader(200, {
  "Content-Length": body.length,
  "Content-Type": "text/plain"

This method must only be called once on a message and it must be called before response.finish() is called.

response.sendBody(chunk, encoding="ascii")

This method must be called after sendHeader was called. It sends a chunk of the response body. This method may be called multiple times to provide successive parts of the body.

If chunk is a string, the second parameter specifies how to encode it into a byte stream. By default the encoding is "ascii".

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 sendBody is called, it will send the buffered header information and the first body to the client. The second time sendBody is called, Node assumes you’re going to be streaming data, and sends that seperately. That is, the response is buffered up to the first chunk of body.


This method signals to the server that all of the response headers and body has been sent; that server should consider this message complete. The method, response.finish(), MUST be called on each response.


An HTTP client is constructed with a server address as its argument, the returned handle is then used to issue one or more requests. Depending on the server connected to, the client might pipeline the requests or reestablish the connection after each connection. Currently the implementation does not pipeline requests.

Example of connecting to

var sys = require("sys"),
   http = require("http");
var google = http.createClient(80, "");
var request = google.get("/", {"host": ""});
request.finish(function (response) {
  sys.puts("STATUS: " + response.statusCode);
  sys.puts("HEADERS: " + JSON.stringify(response.headers));
  response.addListener("body", function (chunk) {
    sys.puts("BODY: " + chunk);
http.createClient(port, host)

Constructs a new HTTP client. port and host refer to the server to be connected to. A connection is not established until a request is issued.

client.get(path, request_headers), client.head(path, request_headers),, request_headers), client.del(path, request_headers), client.put(path, request_headers)

Issues a request; if necessary establishes connection. Returns a http.ClientRequest instance.

request_headers is optional. Additional request headers might be added internally by Node. Returns a ClientRequest object.

Do remember to include the Content-Length header if you plan on sending a body. If you plan on streaming the body, perhaps set Transfer-Encoding: chunked.

the request is not complete. This method only sends the header of the request. One needs to call request.finish() to finalize the request and retrieve the response. (This sounds convoluted but it provides a chance for the user to stream a body to the server with request.sendBody().)


This object is created internally and returned from the request methods of a http.Client. It represents an in-progress request whose header has already been sent.

Event Parameters Notes



Emitted when a response is received to this request. Typically the user will set a listener to this via the request.finish() method.
This event is emitted only once.
The response argument will be an instance of http.ClientResponse.

request.sendBody(chunk, encoding="ascii")

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 chunk argument should be an array of integers or a string.

The encoding argument is optional and only applies when chunk is a string. The encoding argument should be either "utf8" or "ascii". By default the body uses ASCII encoding, as it is faster.


Finishes sending the request. If any parts of the body are unsent, it will flush them to the socket. If the request is chunked, this will send the terminating "0\r\n\r\n".

The parameter responseListener is a callback which will be executed when the response headers have been received. The responseListener callback is executed with one argument which is an instance of http.ClientResponse.

In the responseListener callback, one can add more listeners to the response, in particular listening for the "body" event. Note that the responseListener is called before any part of the body is receieved, so there is no need to worry about racing to catch the first part of the body. As long as a listener for "body" is added during the responseListener callback, the entire body will be caught.

// Good
request.finish(function (response) {
  response.addListener("body", function (chunk) {
    puts("BODY: " + chunk);

// Bad - misses all or part of the body
request.finish(function (response) {
  setTimeout(function () {
    response.addListener("body", function (chunk) {
      puts("BODY: " + chunk);
  }, 10);


This object is created internally and passed to the "response" event.

Event Parameters Notes



Emitted when a piece of the message body is received. Example: A chunk of the body is given as the single argument. The transfer-encoding has been decoded. The body chunk a String. The body encoding is set with response.setBodyEncoding().


Emitted exactly once for each message. No arguments. After emitted no other events will be emitted on the response.


The 3-digit HTTP response status code. E.G. 404.


The HTTP version of the connected-to server. Probably either "1.1" or "1.0".


The response headers.


Set the encoding for the response body. Either "utf8" or "binary". Defaults to "binary".


Pauses response from emitting events. Useful to throttle back a download.


Resumes a paused response.


A reference to the http.Client that this response belongs to.

Multipart Parsing

A library to parse HTTP requests with multipart/form-data is included with Node. To use it, require("multipart").

  • on success: Returns an object where each key holds the value of one part of the stream. options can either be an instance of http.ServerRequest or an object containing a "boundary" and a "data" key.

  • on error: no parameters.


Here is an example for parsing a multipart/form-data request:

var multipart = require("multipart");
var stream = new multipart.Stream(options);
var parts = {};

stream.addListener("part", function (part) {
  var name = part.headers["Content-Disposition"].name;
  var buffer = "";

  part.addListener("body", function(chunk) {
    buffer = buffer + chunk;

  part.addListener("complete", function() {
    parts[name] = buffer;

stream.addListener("complete", function() {
  // The parts object now contains all parts and data
Event Parameters Notes



Emitted when a new part is found in the stream. part is an instance of multipart.Part.


Emitted when the end of the stream is reached.


Event Parameters Notes



Emitted when a chunk of body is read.


Emitted when the end of the part is reached.


To use the TCP server and client one must require("tcp").


Here is an example of a echo server which listens for connections on port 7000

var tcp = require("tcp");
var server = tcp.createServer(function (socket) {
  socket.addListener("connect", function () {
  socket.addListener("receive", function (data) {
  socket.addListener("eof", function () {
server.listen(7000, "localhost");
Event Parameters Notes



Emitted when a new connection is made. connection is an instance of tcp.Connection.



Emitted when the server closes. errorno is an integer which indicates what, if any, error caused the server to close. If no error occurred errorno will be 0.


Creates a new TCP server.

The connection_listener argument is automatically set as a listener for the "connection" event.

server.listen(port, host=null, backlog=128)

Tells the server to listen for TCP connections to port and host.

host is optional. If host is not specified the server will accept client connections on any network address.

The third argument, backlog, is also optional and defaults to 128. The backlog argument defines the maximum length to which the queue of pending connections for the server may grow.

This function is synchronous.


Stops the server from accepting new connections. This function is asynchronous, the server is finally closed when the server emits a "close" event.


This object is used as a TCP client and also as a server-side socket for tcp.Server.

Event Parameters Notes


Call once the connection is established after a call to createConnection() or connect().



Called when data is received on the connection. data will be a string. Encoding of data is set by connection.setEncoding().


Called when the other end of the connection sends a FIN packet. After this is emitted the readyState will be "writeOnly". One should probably just call connection.close() when this event is emitted.


Emitted if the connection times out from inactivity. The "close" event will be emitted immediately following this event.



Emitted once the connection is fully closed. The argument had_error is a boolean which says if the connection was closed due to a transmission error. (TODO: access error codes.)

tcp.createConnection(port, host="")

Creates a new connection object and opens a connection to the specified port and host. If the second parameter is omitted, localhost is assumed.

When the connection is established the "connect" event will be emitted.

connection.connect(port, host="")

Opens a connection to the specified port and host. createConnection() also opens a connection; normally this method is not needed. Use this only if a connection is closed and you want to reuse the object to connect to another server.

This function is asynchronous. When the "connect" event is emitted the connection is established. If there is a problem connecting, the "connect" event will not be emitted, the "close" event will be emitted with had_error == true.


The string representation of the remote IP address. For example, "" or "2001:4860:a005::68".

This member is only present in server-side connections.


Either "closed", "open", "opening", "readOnly", or "writeOnly".


Sets the encoding (either "ascii", "utf8", or "binary") for data that is received.

connection.send(data, encoding="ascii")

Sends data on the connection. The second parameter specifies the encoding in the case of a string—it defaults to ASCII because encoding to UTF8 is rather slow.


Half-closes the connection. I.E., it sends a FIN packet. It is possible the server will still send some data. After calling this readyState will be "readOnly".


Ensures that no more I/O activity happens on this socket. Only necessary in case of errors (parse error or so).


Pauses the reading of data. That is, "receive" events will not be emitted. Useful to throttle back an upload.


Resumes reading if reading was paused by readPause().


Sets the connection to timeout after timeout milliseconds of inactivity on the connection. By default all tcp.Connection objects have a timeout of 60 seconds (60000 ms).

If timeout is 0, then the idle timeout is disabled.


Disables the Nagle algorithm. By default TCP connections use the Nagle algorithm, they buffer data before sending it off. Setting noDelay will immediately fire off data each time connection.send() is called.

DNS module

Use require("dns") to access this module

Here is an example of which resolves "" then reverse resolves the IP addresses which are returned.

var dns = require("dns");

var resolution = dns.resolve4("");

resolution.addCallback(function (addresses, ttl, cname) {
  puts("addresses: " + JSON.stringify(addresses));
  puts("ttl: " + JSON.stringify(ttl));
  puts("cname: " + JSON.stringify(cname));

  for (var i = 0; i < addresses.length; i++) {
    var a = addresses[i];
    var reversing = dns.reverse(a);
    reversing.addCallback( function (domains, ttl, cname) {
      puts("reverse for " + a + ": " + JSON.stringify(domains));
    reversing.addErrback( function (code, msg) {
      puts("reverse for " + a + " failed: " + msg);

resolution.addErrback(function (code, msg) {
  puts("error: " + msg);

Resolves a domain (e.g. "") into an array of IPv4 addresses (e.g. ["", "", ""]). This function returns a promise.

  • on success: returns addresses, ttl, cname. ttl (time-to-live) is an integer specifying the number of seconds this result is valid for. cname is the canonical name for the query.

  • on error: returns code, msg. code is one of the error codes listed below and msg is a string describing the error in English.


The same as dns.resolve4() except for IPv6 queries (an AAAA query).


Reverse resolves an ip address to an array of domain names.

  • on success: returns domains, ttl, cname. ttl (time-to-live) is an integer specifying the number of seconds this result is valid for. cname is the canonical name for the query. domains is an array of domains.

  • on error: returns code, msg. code is one of the error codes listed below and msg is a string describing the error in English.

Each DNS query can return an error code.

  • dns.TEMPFAIL: timeout, SERVFAIL or similar.

  • dns.PROTOCOL: got garbled reply.

  • dns.NXDOMAIN: domain does not exists.

  • dns.NODATA: domain exists but no data of reqd type.

  • dns.NOMEM: out of memory while processing.

  • dns.BADQUERY: the query is malformed.


A Read-Eval-Print-Loop is available both as a standalone program and easily includable in other programs.

The standalone REPL is called node-repl and is installed at $PREFIX/bin/node-repl. It’s recommended to use it with the program rlwrap for a better user interface. I set

alias node-repl="rlwrap node-repl"

in my zsh configuration.

Inside the REPL, Control+D will exit. The special variable _ (underscore) contains the result of the last expression.

The library is called /repl.js and it can be used like this:

var sys = require("sys"),
    tcp = require("tcp"),
   repl = require("repl");
nconnections = 0;
tcp.createServer(function (c) {
  nconnections += 1;
repl.start("simple tcp server> ");


Addons are dynamically linked shared objects. They can provide glue to C and C++ libraries. The API (at the moment) is rather complex, involving knowledge of several libraries:

  • V8 Javascript, a C++ library. Used for interfacing with Javascript: creating objects, calling functions, etc. Documented mostly in the v8.h header file (deps/v8/include/v8.h in the Node source tree).

  • libev, C event loop library. Anytime one needs to wait for a file descriptor to become readable, wait for a timer, or wait for a signal to received one will need to interface with libev. That is, if you perform any I/O, libev will need to be used. Node uses the EV_DEFAULT event loop. Documentation can be found here.

  • libeio, C thread pool library. Used to execute blocking POSIX system calls asynchronously. Mostly wrappers already exist for such calls, in src/ so you will probably not need to use it. If you do need it, look at the header file deps/libeio/eio.h.

  • Internal Node libraries. Most importantly is the node::EventEmitter class which you will likely want to derive from.

  • Others. Look in deps/ for what else is available.

Node statically compiles all its dependencies into the executable. When compiling your module, you don’t need to worry about linking to any of these libraries.

To get started let’s make a small Addon which does the following except in C++:

exports.hello = "world";

To get started we create a file

#include <v8.h>

using namespace v8;

extern "C" void
init (Handle<Object> target)
  HandleScope scope;
  target->Set(String::New("hello"), String::New("World"));

This source code needs to be built into hello.node, the binary Addon. To do this we create a file called wscript which is python code and looks like this:

srcdir = "."
blddir = "build"
VERSION = "0.0.1"

def set_options(opt):

def configure(conf):

def build(bld):
  obj = bld.new_task_gen("cxx", "shlib", "node_addon") = "hello"
  obj.source = ""

Running node-waf configure build will create a file build/default/hello.node which is our Addon.

node-waf is just WAF, the python-based build system. node-waf is provided for the ease of users.

All Node addons must export a function called init with this signature:

extern "C" void init (Handle<Object> target)

For the moment, that is all the documentation on addons. Please see node_postgres for a real example.