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Node.js v14.15.5-rc.0 Documentation
Table of Contents
- Buffer
- Buffers and character encodings
- Buffers and TypedArrays
- Buffers and iteration
- Class:
Buffer
- Static method:
Buffer.alloc(size[, fill[, encoding]])
- Static method:
Buffer.allocUnsafe(size)
- Static method:
Buffer.allocUnsafeSlow(size)
- Static method:
Buffer.byteLength(string[, encoding])
- Static method:
Buffer.compare(buf1, buf2)
- Static method:
Buffer.concat(list[, totalLength])
- Static method:
Buffer.from(array)
- Static method:
Buffer.from(arrayBuffer[, byteOffset[, length]])
- Static method:
Buffer.from(buffer)
- Static method:
Buffer.from(object[, offsetOrEncoding[, length]])
- Static method:
Buffer.from(string[, encoding])
- Static method:
Buffer.isBuffer(obj)
- Static method:
Buffer.isEncoding(encoding)
- Class property:
Buffer.poolSize
buf[index]
buf.buffer
buf.byteOffset
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.keys()
buf.lastIndexOf(value[, byteOffset][, encoding])
buf.length
buf.parent
buf.readBigInt64BE([offset])
buf.readBigInt64LE([offset])
buf.readBigUInt64BE([offset])
buf.readBigUInt64LE([offset])
buf.readDoubleBE([offset])
buf.readDoubleLE([offset])
buf.readFloatBE([offset])
buf.readFloatLE([offset])
buf.readInt8([offset])
buf.readInt16BE([offset])
buf.readInt16LE([offset])
buf.readInt32BE([offset])
buf.readInt32LE([offset])
buf.readIntBE(offset, byteLength)
buf.readIntLE(offset, byteLength)
buf.readUInt8([offset])
buf.readUInt16BE([offset])
buf.readUInt16LE([offset])
buf.readUInt32BE([offset])
buf.readUInt32LE([offset])
buf.readUIntBE(offset, byteLength)
buf.readUIntLE(offset, byteLength)
buf.subarray([start[, end]])
buf.slice([start[, end]])
buf.swap16()
buf.swap32()
buf.swap64()
buf.toJSON()
buf.toString([encoding[, start[, end]]])
buf.values()
buf.write(string[, offset[, length]][, encoding])
buf.writeBigInt64BE(value[, offset])
buf.writeBigInt64LE(value[, offset])
buf.writeBigUInt64BE(value[, offset])
buf.writeBigUInt64LE(value[, offset])
buf.writeDoubleBE(value[, offset])
buf.writeDoubleLE(value[, offset])
buf.writeFloatBE(value[, offset])
buf.writeFloatLE(value[, offset])
buf.writeInt8(value[, offset])
buf.writeInt16BE(value[, offset])
buf.writeInt16LE(value[, offset])
buf.writeInt32BE(value[, offset])
buf.writeInt32LE(value[, offset])
buf.writeIntBE(value, offset, byteLength)
buf.writeIntLE(value, offset, byteLength)
buf.writeUInt8(value[, offset])
buf.writeUInt16BE(value[, offset])
buf.writeUInt16LE(value[, offset])
buf.writeUInt32BE(value[, offset])
buf.writeUInt32LE(value[, offset])
buf.writeUIntBE(value, offset, byteLength)
buf.writeUIntLE(value, offset, byteLength)
new Buffer(array)
new Buffer(arrayBuffer[, byteOffset[, length]])
new Buffer(buffer)
new Buffer(size)
new Buffer(string[, encoding])
- Static method:
buffer
module APIsBuffer.from()
,Buffer.alloc()
, andBuffer.allocUnsafe()
Buffer#
Source Code: lib/buffer.js
Buffer
objects are used to represent a fixed-length sequence of bytes. Many
Node.js APIs support Buffer
s.
The Buffer
class is a subclass of JavaScript's Uint8Array
class and
extends it with methods that cover additional use cases. Node.js APIs accept
plain Uint8Array
s wherever Buffer
s are supported as well.
The Buffer
class is within the global scope, making it unlikely that one
would need to ever use require('buffer').Buffer
.
// Creates a zero-filled Buffer of length 10.
const buf1 = Buffer.alloc(10);
// Creates a Buffer of length 10,
// filled with bytes which all have the value `1`.
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 fill(), write(), or other functions that fill the Buffer's
// contents.
const buf3 = Buffer.allocUnsafe(10);
// Creates a Buffer containing the bytes [1, 2, 3].
const buf4 = Buffer.from([1, 2, 3]);
// Creates a Buffer containing the bytes [1, 1, 1, 1] – the entries
// are all truncated using `(value & 255)` to fit into the range 0–255.
const buf5 = Buffer.from([257, 257.5, -255, '1']);
// Creates a Buffer containing the UTF-8-encoded bytes for the string 'tést':
// [0x74, 0xc3, 0xa9, 0x73, 0x74] (in hexadecimal notation)
// [116, 195, 169, 115, 116] (in decimal notation)
const buf6 = Buffer.from('tést');
// Creates a Buffer containing the Latin-1 bytes [0x74, 0xe9, 0x73, 0x74].
const buf7 = Buffer.from('tést', 'latin1');
Buffers and character encodings#
When converting between Buffer
s and strings, a character encoding may be
specified. If no character encoding is specified, UTF-8 will be used as the
default.
const buf = Buffer.from('hello world', 'utf8');
console.log(buf.toString('hex'));
// Prints: 68656c6c6f20776f726c64
console.log(buf.toString('base64'));
// Prints: aGVsbG8gd29ybGQ=
console.log(Buffer.from('fhqwhgads', 'utf8'));
// Prints: <Buffer 66 68 71 77 68 67 61 64 73>
console.log(Buffer.from('fhqwhgads', 'utf16le'));
// Prints: <Buffer 66 00 68 00 71 00 77 00 68 00 67 00 61 00 64 00 73 00>
The character encodings currently supported by Node.js are the following:
-
'utf8'
: Multi-byte encoded Unicode characters. Many web pages and other document formats use UTF-8. This is the default character encoding. When decoding aBuffer
into a string that does not exclusively contain valid UTF-8 data, the Unicode replacement characterU+FFFD
� will be used to represent those errors. -
'utf16le'
: Multi-byte encoded Unicode characters. Unlike'utf8'
, each character in the string will be encoded using either 2 or 4 bytes. Node.js only supports the little-endian variant of UTF-16. -
'latin1'
: Latin-1 stands for ISO-8859-1. This character encoding only supports the Unicode characters fromU+0000
toU+00FF
. Each character is encoded using a single byte. Characters that do not fit into that range are truncated and will be mapped to characters in that range.
Converting a Buffer
into a string using one of the above is referred to as
decoding, and converting a string into a Buffer
is referred to as encoding.
Node.js also supports the following two binary-to-text encodings. For
binary-to-text encodings, the naming convention is reversed: Converting a
Buffer
into a string is typically referred to as encoding, and converting a
string into a Buffer
as decoding.
-
'base64'
: Base64 encoding. When creating aBuffer
from a string, this encoding will also correctly accept "URL and Filename Safe Alphabet" as specified in RFC 4648, Section 5. Whitespace characters such as spaces, tabs, and new lines contained within the base64-encoded string are ignored. -
'hex'
: Encode each byte as two hexadecimal characters. Data truncation may occur when decoding strings that do exclusively contain valid hexadecimal characters. See below for an example.
The following legacy character encodings are also supported:
-
'ascii'
: For 7-bit ASCII data only. When encoding a string into aBuffer
, this is equivalent to using'latin1'
. When decoding aBuffer
into a string, using this encoding will additionally unset the highest bit of each byte before decoding as'latin1'
. Generally, there should be no reason to use this encoding, as'utf8'
(or, if the data is known to always be ASCII-only,'latin1'
) will be a better choice when encoding or decoding ASCII-only text. It is only provided for legacy compatibility. -
'binary'
: Alias for'latin1'
. See binary strings for more background on this topic. The name of this encoding can be very misleading, as all of the encodings listed here convert between strings and binary data. For converting between strings andBuffer
s, typically'utf-8'
is the right choice. -
'ucs2'
: Alias of'utf16le'
. UCS-2 used to refer to a variant of UTF-16 that did not support characters that had code points larger than U+FFFF. In Node.js, these code points are always supported.
Buffer.from('1ag', 'hex');
// Prints <Buffer 1a>, data truncated when first non-hexadecimal value
// ('g') encountered.
Buffer.from('1a7g', 'hex');
// Prints <Buffer 1a>, data truncated when data ends in single digit ('7').
Buffer.from('1634', 'hex');
// Prints <Buffer 16 34>, all data represented.
Modern Web browsers follow the WHATWG Encoding Standard 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 specification it is possible that the server actually returned
'win-1252'
-encoded data, and using 'latin1'
encoding may incorrectly decode
the characters.
Buffers and TypedArrays#
Buffer
instances are also JavaScript Uint8Array
and TypedArray
instances. All TypedArray
methods are available on Buffer
s. There are,
however, subtle incompatibilities between the Buffer
API and the
TypedArray
API.
In particular:
- While
TypedArray#slice()
creates a copy of part of theTypedArray
,Buffer#slice()
creates a view over the existingBuffer
without copying. This behavior can be surprising, and only exists for legacy compatibility.TypedArray#subarray()
can be used to achieve the behavior ofBuffer#slice()
on bothBuffer
s and otherTypedArray
s. buf.toString()
is incompatible with itsTypedArray
equivalent.- A number of methods, e.g.
buf.indexOf()
, support additional arguments.
There are two ways to create new TypedArray
instances from a Buffer
:
- Passing a
Buffer
to aTypedArray
constructor will copy theBuffer
s contents, interpreted as an array of integers, and not as a byte sequence of the target type.
const buf = Buffer.from([1, 2, 3, 4]);
const uint32array = new Uint32Array(buf);
console.log(uint32array);
// Prints: Uint32Array(4) [ 1, 2, 3, 4 ]
- Passing the
Buffer
s underlyingArrayBuffer
will create aTypedArray
that shares its memory with theBuffer
.
const buf = Buffer.from('hello', 'utf16le');
const uint16arr = new Uint16Array(
buf.buffer,
buf.byteOffset,
buf.length / Uint16Array.BYTES_PER_ELEMENT);
console.log(uint16array);
// Prints: Uint16Array(5) [ 104, 101, 108, 108, 111 ]
It is possible to create a new Buffer
that shares the same allocated
memory as a TypedArray
instance by using the TypedArray
object’s
.buffer
property in the same way. Buffer.from()
behaves like new Uint8Array()
in this context.
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);
console.log(buf1);
// Prints: <Buffer 88 a0>
console.log(buf2);
// Prints: <Buffer 88 13 a0 0f>
arr[1] = 6000;
console.log(buf1);
// Prints: <Buffer 88 a0>
console.log(buf2);
// Prints: <Buffer 88 13 70 17>
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.
const arr = new Uint16Array(20);
const buf = Buffer.from(arr.buffer, 0, 16);
console.log(buf.length);
// Prints: 16
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 iteration#
Buffer
instances can be iterated over using for..of
syntax:
const buf = Buffer.from([1, 2, 3]);
for (const b of buf) {
console.log(b);
}
// Prints:
// 1
// 2
// 3
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.
Static method: Buffer.alloc(size[, fill[, encoding]])
#
size
<integer> The desired length of the newBuffer
.fill
<string> | <Buffer> | <Uint8Array> | <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.
const buf = Buffer.alloc(5);
console.log(buf);
// Prints: <Buffer 00 00 00 00 00>
If size
is larger than
buffer.constants.MAX_LENGTH
or smaller than 0, ERR_INVALID_OPT_VALUE
is thrown.
If fill
is specified, the allocated Buffer
will be initialized by calling
buf.fill(fill)
.
const buf = Buffer.alloc(5, 'a');
console.log(buf);
// Prints: <Buffer 61 61 61 61 61>
If both fill
and encoding
are specified, the allocated Buffer
will be
initialized by calling buf.fill(fill, encoding)
.
const buf = Buffer.alloc(11, 'aGVsbG8gd29ybGQ=', 'base64');
console.log(buf);
// Prints: <Buffer 68 65 6c 6c 6f 20 77 6f 72 6c 64>
Calling Buffer.alloc()
can be measurably slower than the alternative
Buffer.allocUnsafe()
but ensures that the newly created Buffer
instance
contents will never contain sensitive data from previous allocations, including
data that might not have been allocated for Buffer
s.
A TypeError
will be thrown if size
is not a number.
Static method: Buffer.allocUnsafe(size)
#
size
<integer> The desired length of the newBuffer
.
Allocates a new Buffer
of size
bytes. If size
is larger than
buffer.constants.MAX_LENGTH
or smaller than 0, ERR_INVALID_OPT_VALUE
is thrown.
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 with zeroes.
const buf = Buffer.allocUnsafe(10);
console.log(buf);
// Prints (contents may vary): <Buffer a0 8b 28 3f 01 00 00 00 50 32>
buf.fill(0);
console.log(buf);
// Prints: <Buffer 00 00 00 00 00 00 00 00 00 00>
A TypeError
will be thrown if size
is not a number.
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()
,
Buffer.from(array)
, Buffer.concat()
, 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.
Static method: Buffer.allocUnsafeSlow(size)
#
size
<integer> The desired length of the newBuffer
.
Allocates a new Buffer
of size
bytes. If size
is larger than
buffer.constants.MAX_LENGTH
or smaller than 0, ERR_INVALID_OPT_VALUE
is thrown. A zero-length Buffer
is created if size
is 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 with zeroes.
When using Buffer.allocUnsafe()
to allocate new Buffer
instances,
allocations under 4KB are 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 clean up as
many individual ArrayBuffer
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()
and
then copying out the relevant bits.
// Need to keep around a few small chunks of memory.
const store = [];
socket.on('readable', () => {
let data;
while (null !== (data = readable.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);
}
});
A TypeError
will be thrown if size
is not a number.
Static 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 byte length of a string when encoded using encoding
.
This is not the same as String.prototype.length
, which does not account
for the encoding that is used to convert the string into bytes.
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.
const str = '\u00bd + \u00bc = \u00be';
console.log(`${str}: ${str.length} characters, ` +
`${Buffer.byteLength(str, 'utf8')} bytes`);
// Prints: ½ + ¼ = ¾: 9 characters, 12 bytes
When string
is a Buffer
/DataView
/TypedArray
/ArrayBuffer
/
SharedArrayBuffer
, the byte length as reported by .byteLength
is returned.
Static method: Buffer.compare(buf1, buf2)
#
buf1
<Buffer> | <Uint8Array>buf2
<Buffer> | <Uint8Array>- Returns: <integer> Either
-1
,0
, or1
, depending on the result of the comparison. Seebuf.compare()
for details.
Compares buf1
to buf2
, typically for the purpose of sorting arrays of
Buffer
instances. This is equivalent to calling
buf1.compare(buf2)
.
const buf1 = Buffer.from('1234');
const buf2 = Buffer.from('0123');
const arr = [buf1, buf2];
console.log(arr.sort(Buffer.compare));
// Prints: [ <Buffer 30 31 32 33>, <Buffer 31 32 33 34> ]
// (This result is equal to: [buf2, buf1].)
Static method: Buffer.concat(list[, totalLength])
#
list
<Buffer[]> | <Uint8Array[]> List ofBuffer
orUint8Array
instances to concatenate.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
by adding their lengths.
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
.
// 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;
console.log(totalLength);
// Prints: 42
const bufA = Buffer.concat([buf1, buf2, buf3], totalLength);
console.log(bufA);
// Prints: <Buffer 00 00 00 00 ...>
console.log(bufA.length);
// Prints: 42
Buffer.concat()
may also use the internal Buffer
pool like
Buffer.allocUnsafe()
does.
Static method: Buffer.from(array)
#
array
<integer[]>
Allocates a new Buffer
using an array
of bytes in the range 0
– 255
.
Array entries outside that range will be truncated to fit into it.
// Creates a new Buffer containing the 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
or another type
appropriate for Buffer.from()
variants.
Buffer.from(array)
and Buffer.from(string)
may also use the internal
Buffer
pool like Buffer.allocUnsafe()
does.
Static method: Buffer.from(arrayBuffer[, byteOffset[, length]])
#
arrayBuffer
<ArrayBuffer> | <SharedArrayBuffer> AnArrayBuffer
,SharedArrayBuffer
, for example the.buffer
property of aTypedArray
.byteOffset
<integer> Index of first byte to expose. Default:0
.length
<integer> Number of bytes to expose. Default:arrayBuffer.byteLength - 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
.
const arr = new Uint16Array(2);
arr[0] = 5000;
arr[1] = 4000;
// Shares memory with `arr`.
const buf = Buffer.from(arr.buffer);
console.log(buf);
// Prints: <Buffer 88 13 a0 0f>
// Changing the original Uint16Array changes the Buffer also.
arr[1] = 6000;
console.log(buf);
// Prints: <Buffer 88 13 70 17>
The optional byteOffset
and length
arguments specify a memory range within
the arrayBuffer
that will be shared by the Buffer
.
const ab = new ArrayBuffer(10);
const buf = Buffer.from(ab, 0, 2);
console.log(buf.length);
// Prints: 2
A TypeError
will be thrown if arrayBuffer
is not an ArrayBuffer
or a
SharedArrayBuffer
or another type appropriate for Buffer.from()
variants.
Static method: Buffer.from(buffer)
#
buffer
<Buffer> | <Uint8Array> An existingBuffer
orUint8Array
from which to copy data.
Copies the passed buffer
data onto a new Buffer
instance.
const buf1 = Buffer.from('buffer');
const buf2 = Buffer.from(buf1);
buf1[0] = 0x61;
console.log(buf1.toString());
// Prints: auffer
console.log(buf2.toString());
// Prints: buffer
A TypeError
will be thrown if buffer
is not a Buffer
or another type
appropriate for Buffer.from()
variants.
Static method: Buffer.from(object[, offsetOrEncoding[, length]])
#
object
<Object> An object supportingSymbol.toPrimitive
orvalueOf()
.offsetOrEncoding
<integer> | <string> A byte-offset or encoding.length
<integer> A length.
For objects whose valueOf()
function returns a value not strictly equal to
object
, returns Buffer.from(object.valueOf(), offsetOrEncoding, length)
.
const buf = Buffer.from(new String('this is a test'));
// Prints: <Buffer 74 68 69 73 20 69 73 20 61 20 74 65 73 74>
For objects that support Symbol.toPrimitive
, returns
Buffer.from(object[Symbol.toPrimitive]('string'), offsetOrEncoding)
.
class Foo {
[Symbol.toPrimitive]() {
return 'this is a test';
}
}
const buf = Buffer.from(new Foo(), 'utf8');
// Prints: <Buffer 74 68 69 73 20 69 73 20 61 20 74 65 73 74>
A TypeError
will be thrown if object
does not have the mentioned methods or
is not of another type appropriate for Buffer.from()
variants.
Static method: Buffer.from(string[, encoding])
#
Creates a new Buffer
containing string
. The encoding
parameter identifies
the character encoding to be used when converting string
into bytes.
const buf1 = Buffer.from('this is a tést');
const buf2 = Buffer.from('7468697320697320612074c3a97374', 'hex');
console.log(buf1.toString());
// Prints: this is a tést
console.log(buf2.toString());
// Prints: this is a tést
console.log(buf1.toString('latin1'));
// Prints: this is a tést
A TypeError
will be thrown if string
is not a string or another type
appropriate for Buffer.from()
variants.
Static method: Buffer.isBuffer(obj)
#
Returns true
if obj
is a Buffer
, false
otherwise.
Static method: Buffer.isEncoding(encoding)
#
Returns true
if encoding
is the name of a supported character encoding,
or false
otherwise.
console.log(Buffer.isEncoding('utf-8'));
// Prints: true
console.log(Buffer.isEncoding('hex'));
// Prints: true
console.log(Buffer.isEncoding('utf/8'));
// Prints: false
console.log(Buffer.isEncoding(''));
// Prints: false
Class property: Buffer.poolSize
#
- <integer> Default:
8192
This is the size (in bytes) of pre-allocated internal Buffer
instances used
for pooling. This value may be modified.
buf[index]
#
index
<integer>
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
. In other words, buf[index]
returns
undefined
when index
is negative or greater or equal to buf.length
, and
buf[index] = value
does not modify the buffer if index
is negative or
>= buf.length
.
// Copy an ASCII string into a `Buffer` one byte at a time.
// (This only works for ASCII-only strings. In general, one should use
// `Buffer.from()` to perform this conversion.)
const str = 'Node.js';
const buf = Buffer.allocUnsafe(str.length);
for (let i = 0; i < str.length; i++) {
buf[i] = str.charCodeAt(i);
}
console.log(buf.toString('utf8'));
// Prints: Node.js
buf.buffer
#
- <ArrayBuffer> The underlying
ArrayBuffer
object based on which thisBuffer
object is created.
This ArrayBuffer
is not guaranteed to correspond exactly to the original
Buffer
. See the notes on buf.byteOffset
for details.
const arrayBuffer = new ArrayBuffer(16);
const buffer = Buffer.from(arrayBuffer);
console.log(buffer.buffer === arrayBuffer);
// Prints: true
buf.byteOffset
#
- <integer> The
byteOffset
of theBuffer
s underlyingArrayBuffer
object.
When setting byteOffset
in Buffer.from(ArrayBuffer, byteOffset, length)
,
or sometimes when allocating a Buffer
smaller than Buffer.poolSize
, the
buffer does not start from a zero offset on the underlying ArrayBuffer
.
This can cause problems when accessing the underlying ArrayBuffer
directly
using buf.buffer
, as other parts of the ArrayBuffer
may be unrelated
to the Buffer
object itself.
A common issue when creating a TypedArray
object that shares its memory with
a Buffer
is that in this case one needs to specify the byteOffset
correctly:
// Create a buffer smaller than `Buffer.poolSize`.
const nodeBuffer = new Buffer.from([0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);
// When casting the Node.js Buffer to an Int8Array, use the byteOffset
// to refer only to the part of `nodeBuffer.buffer` that contains the memory
// for `nodeBuffer`.
new Int8Array(nodeBuffer.buffer, nodeBuffer.byteOffset, nodeBuffer.length);
buf.compare(target[, targetStart[, targetEnd[, sourceStart[, sourceEnd]]]])
#
target
<Buffer> | <Uint8Array> ABuffer
orUint8Array
with which to comparebuf
.targetStart
<integer> The offset withintarget
at which to begin comparison. Default:0
.targetEnd
<integer> The offset withintarget
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.
const buf1 = Buffer.from('ABC');
const buf2 = Buffer.from('BCD');
const buf3 = Buffer.from('ABCD');
console.log(buf1.compare(buf1));
// Prints: 0
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: 1
console.log([buf1, buf2, buf3].sort(Buffer.compare));
// Prints: [ <Buffer 41 42 43>, <Buffer 41 42 43 44>, <Buffer 42 43 44> ]
// (This result is equal to: [buf1, buf3, buf2].)
The optional targetStart
, targetEnd
, sourceStart
, and sourceEnd
arguments can be used to limit the comparison to specific ranges within target
and buf
respectively.
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]);
console.log(buf1.compare(buf2, 5, 9, 0, 4));
// Prints: 0
console.log(buf1.compare(buf2, 0, 6, 4));
// Prints: -1
console.log(buf1.compare(buf2, 5, 6, 5));
// Prints: 1
ERR_OUT_OF_RANGE
is 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 writing. Default:0
.sourceStart
<integer> The offset withinbuf
from which to begin copying. 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
.
TypedArray#set()
performs the same operation, and is available for all
TypedArrays, including Node.js Buffer
s, although it takes different
function arguments.
// Create two `Buffer` instances.
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;
}
// Copy `buf1` bytes 16 through 19 into `buf2` starting at byte 8 of `buf2`.
buf1.copy(buf2, 8, 16, 20);
// This is equivalent to:
// buf2.set(buf1.subarray(16, 20), 8);
console.log(buf2.toString('ascii', 0, 25));
// Prints: !!!!!!!!qrst!!!!!!!!!!!!!
// Create a `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);
console.log(buf.toString());
// Prints: efghijghijklmnopqrstuvwxyz
buf.entries()
#
- Returns: <Iterator>
Creates and returns an iterator of [index, byte]
pairs from the contents
of buf
.
// Log the entire contents of a `Buffer`.
const buf = Buffer.from('buffer');
for (const pair of buf.entries()) {
console.log(pair);
}
// Prints:
// [0, 98]
// [1, 117]
// [2, 102]
// [3, 102]
// [4, 101]
// [5, 114]
buf.equals(otherBuffer)
#
otherBuffer
<Buffer> | <Uint8Array> ABuffer
orUint8Array
with which to comparebuf
.- Returns: <boolean>
Returns true
if both buf
and otherBuffer
have exactly the same bytes,
false
otherwise. Equivalent to
buf.compare(otherBuffer) === 0
.
const buf1 = Buffer.from('ABC');
const buf2 = Buffer.from('414243', 'hex');
const buf3 = Buffer.from('ABCD');
console.log(buf1.equals(buf2));
// Prints: true
console.log(buf1.equals(buf3));
// Prints: false
buf.fill(value[, offset[, end]][, encoding])
#
value
<string> | <Buffer> | <Uint8Array> | <integer> The value with which to fillbuf
.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> The encoding forvalue
ifvalue
is a string. 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:
// Fill a `Buffer` with the ASCII character 'h'.
const b = Buffer.allocUnsafe(50).fill('h');
console.log(b.toString());
// Prints: hhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh
value
is coerced to a uint32
value if it is not a string, Buffer
, or
integer. If the resulting integer is greater than 255
(decimal), buf
will be
filled with value & 255
.
If the final write of a fill()
operation falls on a multi-byte character,
then only the bytes of that character that fit into buf
are written:
// Fill a `Buffer` with character that takes up two bytes in UTF-8.
console.log(Buffer.allocUnsafe(5).fill('\u0222'));
// Prints: <Buffer c8 a2 c8 a2 c8>
If value
contains invalid characters, it is truncated; if no valid
fill data remains, an exception is thrown:
const buf = Buffer.allocUnsafe(5);
console.log(buf.fill('a'));
// Prints: <Buffer 61 61 61 61 61>
console.log(buf.fill('aazz', 'hex'));
// Prints: <Buffer aa aa aa aa aa>
console.log(buf.fill('zz', 'hex'));
// Throws an exception.
buf.includes(value[, byteOffset][, encoding])
#
value
<string> | <Buffer> | <Uint8Array> | <integer> What to search for.byteOffset
<integer> Where to begin searching inbuf
. If negative, then offset is calculated from the end ofbuf
. 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
.
const buf = Buffer.from('this is a buffer');
console.log(buf.includes('this'));
// Prints: true
console.log(buf.includes('is'));
// Prints: true
console.log(buf.includes(Buffer.from('a buffer')));
// Prints: true
console.log(buf.includes(97));
// Prints: true (97 is the decimal ASCII value for 'a')
console.log(buf.includes(Buffer.from('a buffer example')));
// Prints: false
console.log(buf.includes(Buffer.from('a buffer example').slice(0, 8)));
// Prints: true
console.log(buf.includes('this', 4));
// Prints: false
buf.indexOf(value[, byteOffset][, encoding])
#
value
<string> | <Buffer> | <Uint8Array> | <integer> What to search for.byteOffset
<integer> Where to begin searching inbuf
. If negative, then offset is calculated from the end ofbuf
. Default:0
.encoding
<string> Ifvalue
is a string, this is the encoding used to determine the binary representation of the string that will be searched for inbuf
. 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
orUint8Array
,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
.
const buf = Buffer.from('this is a buffer');
console.log(buf.indexOf('this'));
// Prints: 0
console.log(buf.indexOf('is'));
// Prints: 2
console.log(buf.indexOf(Buffer.from('a buffer')));
// Prints: 8
console.log(buf.indexOf(97));
// Prints: 8 (97 is the decimal ASCII value for 'a')
console.log(buf.indexOf(Buffer.from('a buffer example')));
// Prints: -1
console.log(buf.indexOf(Buffer.from('a buffer example').slice(0, 8)));
// Prints: 8
const utf16Buffer = Buffer.from('\u039a\u0391\u03a3\u03a3\u0395', 'utf16le');
console.log(utf16Buffer.indexOf('\u03a3', 0, 'utf16le'));
// Prints: 4
console.log(utf16Buffer.indexOf('\u03a3', -4, 'utf16le'));
// Prints: 6
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. If the result
of coercion is NaN
or 0
, then the entire buffer will be searched. 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', []));
If value
is an empty string or empty Buffer
and byteOffset
is less
than buf.length
, byteOffset
will be returned. If value
is empty and
byteOffset
is at least buf.length
, buf.length
will be returned.
buf.keys()
#
- Returns: <Iterator>
Creates and returns an iterator of buf
keys (indices).
const buf = Buffer.from('buffer');
for (const key of buf.keys()) {
console.log(key);
}
// Prints:
// 0
// 1
// 2
// 3
// 4
// 5
buf.lastIndexOf(value[, byteOffset][, encoding])
#
value
<string> | <Buffer> | <Uint8Array> | <integer> What to search for.byteOffset
<integer> Where to begin searching inbuf
. If negative, then offset is calculated from the end ofbuf
. Default:buf.length - 1
.encoding
<string> Ifvalue
is a string, this is the encoding used to determine the binary representation of the string that will be searched for inbuf
. Default:'utf8'
.- Returns: <integer> The index of the last occurrence of
value
inbuf
, or-1
ifbuf
does not containvalue
.
Identical to buf.indexOf()
, except the last occurrence of value
is found
rather than the first occurrence.
const buf = Buffer.from('this buffer is a buffer');
console.log(buf.lastIndexOf('this'));
// Prints: 0
console.log(buf.lastIndexOf('buffer'));
// Prints: 17
console.log(buf.lastIndexOf(Buffer.from('buffer')));
// Prints: 17
console.log(buf.lastIndexOf(97));
// Prints: 15 (97 is the decimal ASCII value for 'a')
console.log(buf.lastIndexOf(Buffer.from('yolo')));
// Prints: -1
console.log(buf.lastIndexOf('buffer', 5));
// Prints: 5
console.log(buf.lastIndexOf('buffer', 4));
// Prints: -1
const utf16Buffer = Buffer.from('\u039a\u0391\u03a3\u03a3\u0395', 'utf16le');
console.log(utf16Buffer.lastIndexOf('\u03a3', undefined, 'utf16le'));
// Prints: 6
console.log(utf16Buffer.lastIndexOf('\u03a3', -5, 'utf16le'));
// Prints: 4
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', []));
If value
is an empty string or empty Buffer
, byteOffset
will be returned.
buf.length
#
Returns the number of bytes in buf
.
// Create a `Buffer` and write a shorter string to it using UTF-8.
const buf = Buffer.alloc(1234);
console.log(buf.length);
// Prints: 1234
buf.write('some string', 0, 'utf8');
console.log(buf.length);
// Prints: 1234
buf.parent
#
buf.buffer
instead.The buf.parent
property is a deprecated alias for buf.buffer
.
buf.readBigInt64BE([offset])
#
offset
<integer> Number of bytes to skip before starting to read. Must satisfy:0 <= offset <= buf.length - 8
. Default:0
.- Returns: <bigint>
Reads a signed, big-endian 64-bit integer from buf
at the specified offset
.
Integers read from a Buffer
are interpreted as two's complement signed
values.
buf.readBigInt64LE([offset])
#
offset
<integer> Number of bytes to skip before starting to read. Must satisfy:0 <= offset <= buf.length - 8
. Default:0
.- Returns: <bigint>
Reads a signed, little-endian 64-bit integer from buf
at the specified
offset
.
Integers read from a Buffer
are interpreted as two's complement signed
values.
buf.readBigUInt64BE([offset])
#
offset
<integer> Number of bytes to skip before starting to read. Must satisfy:0 <= offset <= buf.length - 8
. Default:0
.- Returns: <bigint>
Reads an unsigned, big-endian 64-bit integer from buf
at the specified
offset
.
const buf = Buffer.from([0x00, 0x00, 0x00, 0x00, 0xff, 0xff, 0xff, 0xff]);
console.log(buf.readBigUInt64BE(0));
// Prints: 4294967295n
buf.readBigUInt64LE([offset])
#
offset
<integer> Number of bytes to skip before starting to read. Must satisfy:0 <= offset <= buf.length - 8
. Default:0
.- Returns: <bigint>
Reads an unsigned, little-endian 64-bit integer from buf
at the specified
offset
.
const buf = Buffer.from([0x00, 0x00, 0x00, 0x00, 0xff, 0xff, 0xff, 0xff]);
console.log(buf.readBigUInt64LE(0));
// Prints: 18446744069414584320n
buf.readDoubleBE([offset])
#
offset
<integer> Number of bytes to skip before starting to read. Must satisfy0 <= offset <= buf.length - 8
. Default:0
.- Returns: <number>
Reads a 64-bit, big-endian double from buf
at the specified offset
.
const buf = Buffer.from([1, 2, 3, 4, 5, 6, 7, 8]);
console.log(buf.readDoubleBE(0));
// Prints: 8.20788039913184e-304
buf.readDoubleLE([offset])
#
offset
<integer> Number of bytes to skip before starting to read. Must satisfy0 <= offset <= buf.length - 8
. Default:0
.- Returns: <number>
Reads a 64-bit, little-endian double from buf
at the specified offset
.
const buf = Buffer.from([1, 2, 3, 4, 5, 6, 7, 8]);
console.log(buf.readDoubleLE(0));
// Prints: 5.447603722011605e-270
console.log(buf.readDoubleLE(1));
// Throws ERR_OUT_OF_RANGE.
buf.readFloatBE([offset])
#
offset
<integer> Number of bytes to skip before starting to read. Must satisfy0 <= offset <= buf.length - 4
. Default:0
.- Returns: <number>
Reads a 32-bit, big-endian float from buf
at the specified offset
.
const buf = Buffer.from([1, 2, 3, 4]);
console.log(buf.readFloatBE(0));
// Prints: 2.387939260590663e-38
buf.readFloatLE([offset])
#
offset
<integer> Number of bytes to skip before starting to read. Must satisfy0 <= offset <= buf.length - 4
. Default:0
.- Returns: <number>
Reads a 32-bit, little-endian float from buf
at the specified offset
.
const buf = Buffer.from([1, 2, 3, 4]);
console.log(buf.readFloatLE(0));
// Prints: 1.539989614439558e-36
console.log(buf.readFloatLE(1));
// Throws ERR_OUT_OF_RANGE.
buf.readInt8([offset])
#
offset
<integer> Number of bytes to skip before starting to read. Must satisfy0 <= offset <= buf.length - 1
. Default:0
.- Returns: <integer>
Reads a signed 8-bit integer from buf
at the specified offset
.
Integers read from a Buffer
are interpreted as two's complement signed values.
const buf = Buffer.from([-1, 5]);
console.log(buf.readInt8(0));
// Prints: -1
console.log(buf.readInt8(1));
// Prints: 5
console.log(buf.readInt8(2));
// Throws ERR_OUT_OF_RANGE.
buf.readInt16BE([offset])
#
offset
<integer> Number of bytes to skip before starting to read. Must satisfy0 <= offset <= buf.length - 2
. Default:0
.- Returns: <integer>
Reads a signed, big-endian 16-bit integer from buf
at the specified offset
.
Integers read from a Buffer
are interpreted as two's complement signed values.
const buf = Buffer.from([0, 5]);
console.log(buf.readInt16BE(0));
// Prints: 5
buf.readInt16LE([offset])
#
offset
<integer> Number of bytes to skip before starting to read. Must satisfy0 <= offset <= buf.length - 2
. Default:0
.- Returns: <integer>
Reads a signed, little-endian 16-bit integer from buf
at the specified
offset
.
Integers read from a Buffer
are interpreted as two's complement signed values.
const buf = Buffer.from([0, 5]);
console.log(buf.readInt16LE(0));
// Prints: 1280
console.log(buf.readInt16LE(1));
// Throws ERR_OUT_OF_RANGE.
buf.readInt32BE([offset])
#
offset
<integer> Number of bytes to skip before starting to read. Must satisfy0 <= offset <= buf.length - 4
. Default:0
.- Returns: <integer>
Reads a signed, big-endian 32-bit integer from buf
at the specified offset
.
Integers read from a Buffer
are interpreted as two's complement signed values.
const buf = Buffer.from([0, 0, 0, 5]);
console.log(buf.readInt32BE(0));
// Prints: 5
buf.readInt32LE([offset])
#
offset
<integer> Number of bytes to skip before starting to read. Must satisfy0 <= offset <= buf.length - 4
. Default:0
.- Returns: <integer>
Reads a signed, little-endian 32-bit integer from buf
at the specified
offset
.
Integers read from a Buffer
are interpreted as two's complement signed values.
const buf = Buffer.from([0, 0, 0, 5]);
console.log(buf.readInt32LE(0));
// Prints: 83886080
console.log(buf.readInt32LE(1));
// Throws ERR_OUT_OF_RANGE.
buf.readIntBE(offset, byteLength)
#
offset
<integer> Number of bytes to skip before starting to read. Must satisfy0 <= offset <= buf.length - byteLength
.byteLength
<integer> Number of bytes to read. Must satisfy0 < byteLength <= 6
.- Returns: <integer>
Reads byteLength
number of bytes from buf
at the specified offset
and interprets the result as a big-endian, two's complement signed value
supporting up to 48 bits of accuracy.
const buf = Buffer.from([0x12, 0x34, 0x56, 0x78, 0x90, 0xab]);
console.log(buf.readIntBE(0, 6).toString(16));
// Prints: 1234567890ab
console.log(buf.readIntBE(1, 6).toString(16));
// Throws ERR_OUT_OF_RANGE.
console.log(buf.readIntBE(1, 0).toString(16));
// Throws ERR_OUT_OF_RANGE.
buf.readIntLE(offset, byteLength)
#
offset
<integer> Number of bytes to skip before starting to read. Must satisfy0 <= offset <= buf.length - byteLength
.byteLength
<integer> Number of bytes to read. Must satisfy0 < byteLength <= 6
.- Returns: <integer>
Reads byteLength
number of bytes from buf
at the specified offset
and interprets the result as a little-endian, two's complement signed value
supporting up to 48 bits of accuracy.
const buf = Buffer.from([0x12, 0x34, 0x56, 0x78, 0x90, 0xab]);
console.log(buf.readIntLE(0, 6).toString(16));
// Prints: -546f87a9cbee
buf.readUInt8([offset])
#
offset
<integer> Number of bytes to skip before starting to read. Must satisfy0 <= offset <= buf.length - 1
. Default:0
.- Returns: <integer>
Reads an unsigned 8-bit integer from buf
at the specified offset
.
const buf = Buffer.from([1, -2]);
console.log(buf.readUInt8(0));
// Prints: 1
console.log(buf.readUInt8(1));
// Prints: 254
console.log(buf.readUInt8(2));
// Throws ERR_OUT_OF_RANGE.
buf.readUInt16BE([offset])
#
offset
<integer> Number of bytes to skip before starting to read. Must satisfy0 <= offset <= buf.length - 2
. Default:0
.- Returns: <integer>
Reads an unsigned, big-endian 16-bit integer from buf
at the specified
offset
.
const buf = Buffer.from([0x12, 0x34, 0x56]);
console.log(buf.readUInt16BE(0).toString(16));
// Prints: 1234
console.log(buf.readUInt16BE(1).toString(16));
// Prints: 3456
buf.readUInt16LE([offset])
#
offset
<integer> Number of bytes to skip before starting to read. Must satisfy0 <= offset <= buf.length - 2
. Default:0
.- Returns: <integer>
Reads an unsigned, little-endian 16-bit integer from buf
at the specified
offset
.
const buf = Buffer.from([0x12, 0x34, 0x56]);
console.log(buf.readUInt16LE(0).toString(16));
// Prints: 3412
console.log(buf.readUInt16LE(1).toString(16));
// Prints: 5634
console.log(buf.readUInt16LE(2).toString(16));
// Throws ERR_OUT_OF_RANGE.
buf.readUInt32BE([offset])
#
offset
<integer> Number of bytes to skip before starting to read. Must satisfy0 <= offset <= buf.length - 4
. Default:0
.- Returns: <integer>
Reads an unsigned, big-endian 32-bit integer from buf
at the specified
offset
.
const buf = Buffer.from([0x12, 0x34, 0x56, 0x78]);
console.log(buf.readUInt32BE(0).toString(16));
// Prints: 12345678
buf.readUInt32LE([offset])
#
offset
<integer> Number of bytes to skip before starting to read. Must satisfy0 <= offset <= buf.length - 4
. Default:0
.- Returns: <integer>
Reads an unsigned, little-endian 32-bit integer from buf
at the specified
offset
.
const buf = Buffer.from([0x12, 0x34, 0x56, 0x78]);
console.log(buf.readUInt32LE(0).toString(16));
// Prints: 78563412
console.log(buf.readUInt32LE(1).toString(16));
// Throws ERR_OUT_OF_RANGE.
buf.readUIntBE(offset, byteLength)
#
offset
<integer> Number of bytes to skip before starting to read. Must satisfy0 <= offset <= buf.length - byteLength
.byteLength
<integer> Number of bytes to read. Must satisfy0 < byteLength <= 6
.- Returns: <integer>
Reads byteLength
number of bytes from buf
at the specified offset
and interprets the result as an unsigned big-endian integer supporting
up to 48 bits of accuracy.
const buf = Buffer.from([0x12, 0x34, 0x56, 0x78, 0x90, 0xab]);
console.log(buf.readUIntBE(0, 6).toString(16));
// Prints: 1234567890ab
console.log(buf.readUIntBE(1, 6).toString(16));
// Throws ERR_OUT_OF_RANGE.
buf.readUIntLE(offset, byteLength)
#
offset
<integer> Number of bytes to skip before starting to read. Must satisfy0 <= offset <= buf.length - byteLength
.byteLength
<integer> Number of bytes to read. Must satisfy0 < byteLength <= 6
.- Returns: <integer>
Reads byteLength
number of bytes from buf
at the specified offset
and interprets the result as an unsigned, little-endian integer supporting
up to 48 bits of accuracy.
const buf = Buffer.from([0x12, 0x34, 0x56, 0x78, 0x90, 0xab]);
console.log(buf.readUIntLE(0, 6).toString(16));
// Prints: ab9078563412
buf.subarray([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.
Specifying end
greater than buf.length
will return the same result as
that of end
equal to buf.length
.
This method is inherited from TypedArray#subarray()
.
Modifying the new Buffer
slice will modify the memory in the original Buffer
because the allocated memory of the two objects overlap.
// Create a `Buffer` with the ASCII alphabet, take a slice, and 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.subarray(0, 3);
console.log(buf2.toString('ascii', 0, buf2.length));
// Prints: abc
buf1[0] = 33;
console.log(buf2.toString('ascii', 0, buf2.length));
// Prints: !bc
Specifying negative indexes causes the slice to be generated relative to the
end of buf
rather than the beginning.
const buf = Buffer.from('buffer');
console.log(buf.subarray(-6, -1).toString());
// Prints: buffe
// (Equivalent to buf.subarray(0, 5).)
console.log(buf.subarray(-6, -2).toString());
// Prints: buff
// (Equivalent to buf.subarray(0, 4).)
console.log(buf.subarray(-5, -2).toString());
// Prints: uff
// (Equivalent to buf.subarray(1, 4).)
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.
This is the same behavior as buf.subarray()
.
This method is not compatible with the Uint8Array.prototype.slice()
,
which is a superclass of Buffer
. To copy the slice, use
Uint8Array.prototype.slice()
.
const buf = Buffer.from('buffer');
const copiedBuf = Uint8Array.prototype.slice.call(buf);
copiedBuf[0]++;
console.log(copiedBuf.toString());
// Prints: cuffer
console.log(buf.toString());
// Prints: buffer
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 ERR_INVALID_BUFFER_SIZE
if buf.length
is not a multiple of 2.
const buf1 = Buffer.from([0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8]);
console.log(buf1);
// Prints: <Buffer 01 02 03 04 05 06 07 08>
buf1.swap16();
console.log(buf1);
// Prints: <Buffer 02 01 04 03 06 05 08 07>
const buf2 = Buffer.from([0x1, 0x2, 0x3]);
buf2.swap16();
// Throws ERR_INVALID_BUFFER_SIZE.
One convenient use of buf.swap16()
is to perform a fast in-place conversion
between UTF-16 little-endian and UTF-16 big-endian:
const buf = Buffer.from('This is little-endian UTF-16', 'utf16le');
buf.swap16(); // Convert to big-endian UTF-16 text.
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 ERR_INVALID_BUFFER_SIZE
if buf.length
is not a multiple of 4.
const buf1 = Buffer.from([0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8]);
console.log(buf1);
// Prints: <Buffer 01 02 03 04 05 06 07 08>
buf1.swap32();
console.log(buf1);
// Prints: <Buffer 04 03 02 01 08 07 06 05>
const buf2 = Buffer.from([0x1, 0x2, 0x3]);
buf2.swap32();
// Throws ERR_INVALID_BUFFER_SIZE.
buf.swap64()
#
- Returns: <Buffer> A reference to
buf
.
Interprets buf
as an array of 64-bit numbers and swaps byte order in-place.
Throws ERR_INVALID_BUFFER_SIZE
if buf.length
is not a multiple of 8.
const buf1 = Buffer.from([0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8]);
console.log(buf1);
// Prints: <Buffer 01 02 03 04 05 06 07 08>
buf1.swap64();
console.log(buf1);
// Prints: <Buffer 08 07 06 05 04 03 02 01>
const buf2 = Buffer.from([0x1, 0x2, 0x3]);
buf2.swap64();
// Throws ERR_INVALID_BUFFER_SIZE.
buf.toJSON()
#
- Returns: <Object>
Returns a JSON representation of buf
. JSON.stringify()
implicitly calls
this function when stringifying a Buffer
instance.
Buffer.from()
accepts objects in the format returned from this method.
In particular, Buffer.from(buf.toJSON())
works like Buffer.from(buf)
.
const buf = Buffer.from([0x1, 0x2, 0x3, 0x4, 0x5]);
const json = JSON.stringify(buf);
console.log(json);
// Prints: {"type":"Buffer","data":[1,2,3,4,5]}
const copy = JSON.parse(json, (key, value) => {
return value && value.type === 'Buffer' ?
Buffer.from(value) :
value;
});
console.log(copy);
// Prints: <Buffer 01 02 03 04 05>
buf.toString([encoding[, start[, end]]])
#
encoding
<string> The character encoding to use. 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
.
If encoding
is 'utf8'
and a byte sequence in the input is not valid UTF-8,
then each invalid byte is replaced with the replacement character U+FFFD
.
The maximum length of a string instance (in UTF-16 code units) is available
as buffer.constants.MAX_STRING_LENGTH
.
const buf1 = Buffer.allocUnsafe(26);
for (let i = 0; i < 26; i++) {
// 97 is the decimal ASCII value for 'a'.
buf1[i] = i + 97;
}
console.log(buf1.toString('utf8'));
// Prints: abcdefghijklmnopqrstuvwxyz
console.log(buf1.toString('utf8', 0, 5));
// Prints: abcde
const buf2 = Buffer.from('tést');
console.log(buf2.toString('hex'));
// Prints: 74c3a97374
console.log(buf2.toString('utf8', 0, 3));
// Prints: té
console.log(buf2.toString(undefined, 0, 3));
// Prints: té
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.
const buf = Buffer.from('buffer');
for (const value of buf.values()) {
console.log(value);
}
// Prints:
// 98
// 117
// 102
// 102
// 101
// 114
for (const value of buf) {
console.log(value);
}
// Prints:
// 98
// 117
// 102
// 102
// 101
// 114
buf.write(string[, offset[, length]][, encoding])
#
string
<string> String to write tobuf
.offset
<integer> Number of bytes to skip before starting to writestring
. Default:0
.length
<integer> Maximum number of bytes to write (written bytes will not exceedbuf.length - offset
). 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 part of string
will be
written. However, partially encoded characters will not be written.
const buf = Buffer.alloc(256);
const len = buf.write('\u00bd + \u00bc = \u00be', 0);
console.log(`${len} bytes: ${buf.toString('utf8', 0, len)}`);
// Prints: 12 bytes: ½ + ¼ = ¾
const buffer = Buffer.alloc(10);
const length = buffer.write('abcd', 8);
console.log(`${length} bytes: ${buffer.toString('utf8', 8, 10)}`);
// Prints: 2 bytes : ab
buf.writeBigInt64BE(value[, offset])
#
value
<bigint> Number to be written tobuf
.offset
<integer> Number of bytes to skip before starting to write. Must satisfy:0 <= offset <= buf.length - 8
. Default:0
.- Returns: <integer>
offset
plus the number of bytes written.
Writes value
to buf
at the specified offset
as big-endian.
value
is interpreted and written as a two's complement signed integer.
const buf = Buffer.allocUnsafe(8);
buf.writeBigInt64BE(0x0102030405060708n, 0);
console.log(buf);
// Prints: <Buffer 01 02 03 04 05 06 07 08>
buf.writeBigInt64LE(value[, offset])
#
value
<bigint> Number to be written tobuf
.offset
<integer> Number of bytes to skip before starting to write. Must satisfy:0 <= offset <= buf.length - 8
. Default:0
.- Returns: <integer>
offset
plus the number of bytes written.
Writes value
to buf
at the specified offset
as little-endian.
value
is interpreted and written as a two's complement signed integer.
const buf = Buffer.allocUnsafe(8);
buf.writeBigInt64LE(0x0102030405060708n, 0);
console.log(buf);
// Prints: <Buffer 08 07 06 05 04 03 02 01>
buf.writeBigUInt64BE(value[, offset])
#
value
<bigint> Number to be written tobuf
.offset
<integer> Number of bytes to skip before starting to write. Must satisfy:0 <= offset <= buf.length - 8
. Default:0
.- Returns: <integer>
offset
plus the number of bytes written.
Writes value
to buf
at the specified offset
as big-endian.
const buf = Buffer.allocUnsafe(8);
buf.writeBigUInt64BE(0xdecafafecacefaden, 0);
console.log(buf);
// Prints: <Buffer de ca fa fe ca ce fa de>
buf.writeBigUInt64LE(value[, offset])
#
value
<bigint> Number to be written tobuf
.offset
<integer> Number of bytes to skip before starting to write. Must satisfy:0 <= offset <= buf.length - 8
. Default:0
.- Returns: <integer>
offset
plus the number of bytes written.
Writes value
to buf
at the specified offset
as little-endian
const buf = Buffer.allocUnsafe(8);
buf.writeBigUInt64LE(0xdecafafecacefaden, 0);
console.log(buf);
// Prints: <Buffer de fa ce ca fe fa ca de>
buf.writeDoubleBE(value[, offset])
#
value
<number> Number to be written tobuf
.offset
<integer> Number of bytes to skip before starting to write. Must satisfy0 <= offset <= buf.length - 8
. Default:0
.- Returns: <integer>
offset
plus the number of bytes written.
Writes value
to buf
at the specified offset
as big-endian. The value
must be a JavaScript number. Behavior is undefined when value
is anything
other than a JavaScript number.
const buf = Buffer.allocUnsafe(8);
buf.writeDoubleBE(123.456, 0);
console.log(buf);
// Prints: <Buffer 40 5e dd 2f 1a 9f be 77>
buf.writeDoubleLE(value[, offset])
#
value
<number> Number to be written tobuf
.offset
<integer> Number of bytes to skip before starting to write. Must satisfy0 <= offset <= buf.length - 8
. Default:0
.- Returns: <integer>
offset
plus the number of bytes written.
Writes value
to buf
at the specified offset
as little-endian. The value
must be a JavaScript number. Behavior is undefined when value
is anything
other than a JavaScript number.
const buf = Buffer.allocUnsafe(8);
buf.writeDoubleLE(123.456, 0);
console.log(buf);
// Prints: <Buffer 77 be 9f 1a 2f dd 5e 40>
buf.writeFloatBE(value[, offset])
#
value
<number> Number to be written tobuf
.offset
<integer> Number of bytes to skip before starting to write. Must satisfy0 <= offset <= buf.length - 4
. Default:0
.- Returns: <integer>
offset
plus the number of bytes written.
Writes value
to buf
at the specified offset
as big-endian. Behavior is
undefined when value
is anything other than a JavaScript number.
const buf = Buffer.allocUnsafe(4);
buf.writeFloatBE(0xcafebabe, 0);
console.log(buf);
// Prints: <Buffer 4f 4a fe bb>
buf.writeFloatLE(value[, offset])
#
value
<number> Number to be written tobuf
.offset
<integer> Number of bytes to skip before starting to write. Must satisfy0 <= offset <= buf.length - 4
. Default:0
.- Returns: <integer>
offset
plus the number of bytes written.
Writes value
to buf
at the specified offset
as little-endian. Behavior is
undefined when value
is anything other than a JavaScript number.
const buf = Buffer.allocUnsafe(4);
buf.writeFloatLE(0xcafebabe, 0);
console.log(buf);
// Prints: <Buffer bb fe 4a 4f>
buf.writeInt8(value[, offset])
#
value
<integer> Number to be written tobuf
.offset
<integer> Number of bytes to skip before starting to write. Must satisfy0 <= offset <= buf.length - 1
. Default:0
.- Returns: <integer>
offset
plus the number of bytes written.
Writes value
to buf
at the specified offset
. value
must be a valid
signed 8-bit integer. Behavior is undefined when value
is anything other than
a signed 8-bit integer.
value
is interpreted and written as a two's complement signed integer.
const buf = Buffer.allocUnsafe(2);
buf.writeInt8(2, 0);
buf.writeInt8(-2, 1);
console.log(buf);
// Prints: <Buffer 02 fe>
buf.writeInt16BE(value[, offset])
#
value
<integer> Number to be written tobuf
.offset
<integer> Number of bytes to skip before starting to write. Must satisfy0 <= offset <= buf.length - 2
. Default:0
.- Returns: <integer>
offset
plus the number of bytes written.
Writes value
to buf
at the specified offset
as big-endian. The value
must be a valid signed 16-bit integer. Behavior is undefined when value
is
anything other than a signed 16-bit integer.
The value
is interpreted and written as a two's complement signed integer.
const buf = Buffer.allocUnsafe(2);
buf.writeInt16BE(0x0102, 0);
console.log(buf);
// Prints: <Buffer 01 02>
buf.writeInt16LE(value[, offset])
#
value
<integer> Number to be written tobuf
.offset
<integer> Number of bytes to skip before starting to write. Must satisfy0 <= offset <= buf.length - 2
. Default:0
.- Returns: <integer>
offset
plus the number of bytes written.
Writes value
to buf
at the specified offset
as little-endian. The value
must be a valid signed 16-bit integer. Behavior is undefined when value
is
anything other than a signed 16-bit integer.
The value
is interpreted and written as a two's complement signed integer.
const buf = Buffer.allocUnsafe(2);
buf.writeInt16LE(0x0304, 0);
console.log(buf);
// Prints: <Buffer 04 03>
buf.writeInt32BE(value[, offset])
#
value
<integer> Number to be written tobuf
.offset
<integer> Number of bytes to skip before starting to write. Must satisfy0 <= offset <= buf.length - 4
. Default:0
.- Returns: <integer>
offset
plus the number of bytes written.
Writes value
to buf
at the specified offset
as big-endian. The value
must be a valid signed 32-bit integer. Behavior is undefined when value
is
anything other than a signed 32-bit integer.
The value
is interpreted and written as a two's complement signed integer.
const buf = Buffer.allocUnsafe(4);
buf.writeInt32BE(0x01020304, 0);
console.log(buf);
// Prints: <Buffer 01 02 03 04>
buf.writeInt32LE(value[, offset])
#
value
<integer> Number to be written tobuf
.offset
<integer> Number of bytes to skip before starting to write. Must satisfy0 <= offset <= buf.length - 4
. Default:0
.- Returns: <integer>
offset
plus the number of bytes written.
Writes value
to buf
at the specified offset
as little-endian. The value
must be a valid signed 32-bit integer. Behavior is undefined when value
is
anything other than a signed 32-bit integer.
The value
is interpreted and written as a two's complement signed integer.
const buf = Buffer.allocUnsafe(4);
buf.writeInt32LE(0x05060708, 0);
console.log(buf);
// Prints: <Buffer 08 07 06 05>
buf.writeIntBE(value, offset, byteLength)
#
value
<integer> Number to be written tobuf
.offset
<integer> Number of bytes to skip before starting to write. Must satisfy0 <= offset <= buf.length - byteLength
.byteLength
<integer> Number of bytes to write. Must satisfy0 < byteLength <= 6
.- Returns: <integer>
offset
plus the number of bytes written.
Writes byteLength
bytes of value
to buf
at the specified offset
as big-endian. Supports up to 48 bits of accuracy. Behavior is undefined when
value
is anything other than a signed integer.
const buf = Buffer.allocUnsafe(6);
buf.writeIntBE(0x1234567890ab, 0, 6);
console.log(buf);
// Prints: <Buffer 12 34 56 78 90 ab>
buf.writeIntLE(value, offset, byteLength)
#
value
<integer> Number to be written tobuf
.offset
<integer> Number of bytes to skip before starting to write. Must satisfy0 <= offset <= buf.length - byteLength
.byteLength
<integer> Number of bytes to write. Must satisfy0 < byteLength <= 6
.- Returns: <integer>
offset
plus the number of bytes written.
Writes byteLength
bytes of value
to buf
at the specified offset
as little-endian. Supports up to 48 bits of accuracy. Behavior is undefined
when value
is anything other than a signed integer.
const buf = Buffer.allocUnsafe(6);
buf.writeIntLE(0x1234567890ab, 0, 6);
console.log(buf);
// Prints: <Buffer ab 90 78 56 34 12>
buf.writeUInt8(value[, offset])
#
value
<integer> Number to be written tobuf
.offset
<integer> Number of bytes to skip before starting to write. Must satisfy0 <= offset <= buf.length - 1
. Default:0
.- Returns: <integer>
offset
plus the number of bytes written.
Writes value
to buf
at the specified offset
. value
must be a
valid unsigned 8-bit integer. Behavior is undefined when value
is anything
other than an unsigned 8-bit integer.
const buf = Buffer.allocUnsafe(4);
buf.writeUInt8(0x3, 0);
buf.writeUInt8(0x4, 1);
buf.writeUInt8(0x23, 2);
buf.writeUInt8(0x42, 3);
console.log(buf);
// Prints: <Buffer 03 04 23 42>
buf.writeUInt16BE(value[, offset])
#
value
<integer> Number to be written tobuf
.offset
<integer> Number of bytes to skip before starting to write. Must satisfy0 <= offset <= buf.length - 2
. Default:0
.- Returns: <integer>
offset
plus the number of bytes written.
Writes value
to buf
at the specified offset
as big-endian. The value
must be a valid unsigned 16-bit integer. Behavior is undefined when value
is anything other than an unsigned 16-bit integer.
const buf = Buffer.allocUnsafe(4);
buf.writeUInt16BE(0xdead, 0);
buf.writeUInt16BE(0xbeef, 2);
console.log(buf);
// Prints: <Buffer de ad be ef>
buf.writeUInt16LE(value[, offset])
#
value
<integer> Number to be written tobuf
.offset
<integer> Number of bytes to skip before starting to write. Must satisfy0 <= offset <= buf.length - 2
. Default:0
.- Returns: <integer>
offset
plus the number of bytes written.
Writes value
to buf
at the specified offset
as little-endian. The value
must be a valid unsigned 16-bit integer. Behavior is undefined when value
is
anything other than an unsigned 16-bit integer.
const buf = Buffer.allocUnsafe(4);
buf.writeUInt16LE(0xdead, 0);
buf.writeUInt16LE(0xbeef, 2);
console.log(buf);
// Prints: <Buffer ad de ef be>
buf.writeUInt32BE(value[, offset])
#
value
<integer> Number to be written tobuf
.offset
<integer> Number of bytes to skip before starting to write. Must satisfy0 <= offset <= buf.length - 4
. Default:0
.- Returns: <integer>
offset
plus the number of bytes written.
Writes value
to buf
at the specified offset
as big-endian. The value
must be a valid unsigned 32-bit integer. Behavior is undefined when value
is anything other than an unsigned 32-bit integer.
const buf = Buffer.allocUnsafe(4);
buf.writeUInt32BE(0xfeedface, 0);
console.log(buf);
// Prints: <Buffer fe ed fa ce>
buf.writeUInt32LE(value[, offset])
#
value
<integer> Number to be written tobuf
.offset
<integer> Number of bytes to skip before starting to write. Must satisfy0 <= offset <= buf.length - 4
. Default:0
.- Returns: <integer>
offset
plus the number of bytes written.
Writes value
to buf
at the specified offset
as little-endian. The value
must be a valid unsigned 32-bit integer. Behavior is undefined when value
is
anything other than an unsigned 32-bit integer.
const buf = Buffer.allocUnsafe(4);
buf.writeUInt32LE(0xfeedface, 0);
console.log(buf);
// Prints: <Buffer ce fa ed fe>
buf.writeUIntBE(value, offset, byteLength)
#
value
<integer> Number to be written tobuf
.offset
<integer> Number of bytes to skip before starting to write. Must satisfy0 <= offset <= buf.length - byteLength
.byteLength
<integer> Number of bytes to write. Must satisfy0 < byteLength <= 6
.- Returns: <integer>
offset
plus the number of bytes written.
Writes byteLength
bytes of value
to buf
at the specified offset
as big-endian. Supports up to 48 bits of accuracy. Behavior is undefined
when value
is anything other than an unsigned integer.
const buf = Buffer.allocUnsafe(6);
buf.writeUIntBE(0x1234567890ab, 0, 6);
console.log(buf);
// Prints: <Buffer 12 34 56 78 90 ab>
buf.writeUIntLE(value, offset, byteLength)
#
value
<integer> Number to be written tobuf
.offset
<integer> Number of bytes to skip before starting to write. Must satisfy0 <= offset <= buf.length - byteLength
.byteLength
<integer> Number of bytes to write. Must satisfy0 < byteLength <= 6
.- Returns: <integer>
offset
plus the number of bytes written.
Writes byteLength
bytes of value
to buf
at the specified offset
as little-endian. Supports up to 48 bits of accuracy. Behavior is undefined
when value
is anything other than an unsigned integer.
const buf = Buffer.allocUnsafe(6);
buf.writeUIntLE(0x1234567890ab, 0, 6);
console.log(buf);
// Prints: <Buffer ab 90 78 56 34 12>
new Buffer(array)
#
Buffer.from(array)
instead.array
<integer[]> An array of bytes to copy from.
See Buffer.from(array)
.
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.byteLength - byteOffset
.
See
Buffer.from(arrayBuffer[, byteOffset[, length]])
.
new Buffer(buffer)
#
Buffer.from(buffer)
instead.buffer
<Buffer> | <Uint8Array> An existingBuffer
orUint8Array
from which to copy data.
See Buffer.from(buffer)
.
new Buffer(size)
#
size
<integer> The desired length of the newBuffer
.
See Buffer.alloc()
and Buffer.allocUnsafe()
. This variant of the
constructor is equivalent to Buffer.alloc()
.
new Buffer(string[, encoding])
#
Buffer.from(string[, encoding])
instead.See Buffer.from(string[, encoding])
.
buffer
module APIs#
While, the Buffer
object is available as a global, there are additional
Buffer
-related APIs that are available only via the buffer
module
accessed using require('buffer')
.
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.
buffer.kMaxLength
#
- <integer> The largest size allowed for a single
Buffer
instance.
An alias for buffer.constants.MAX_LENGTH
.
buffer.transcode(source, fromEnc, toEnc)
#
source
<Buffer> | <Uint8Array> ABuffer
orUint8Array
instance.fromEnc
<string> The current encoding.toEnc
<string> To target encoding.- Returns: <Buffer>
Re-encodes the given Buffer
or Uint8Array
instance from one character
encoding to another. Returns a new Buffer
instance.
Throws if the fromEnc
or toEnc
specify invalid character encodings or if
conversion from fromEnc
to toEnc
is not permitted.
Encodings supported by buffer.transcode()
are: 'ascii'
, 'utf8'
,
'utf16le'
, 'ucs2'
, 'latin1'
, and 'binary'
.
The transcoding process will use substitution characters if a given byte sequence cannot be adequately represented in the target encoding. For instance:
const buffer = require('buffer');
const newBuf = buffer.transcode(Buffer.from('€'), 'utf8', 'ascii');
console.log(newBuf.toString('ascii'));
// Prints: '?'
Because the Euro (€
) sign is not representable in US-ASCII, it is replaced
with ?
in the transcoded Buffer
.
Class: SlowBuffer
#
Buffer.allocUnsafeSlow()
instead.See Buffer.allocUnsafeSlow()
. This was never a class in the sense that
the constructor always returned a Buffer
instance, rather than a SlowBuffer
instance.
new SlowBuffer(size)
#
Buffer.allocUnsafeSlow()
instead.size
<integer> The desired length of the newSlowBuffer
.
Buffer constants#
buffer.constants.MAX_LENGTH
#
- <integer> The largest size allowed for a single
Buffer
instance.
On 32-bit architectures, this value currently is 230 - 1 (~1GB). On 64-bit architectures, this value currently is 231 - 1 (~2GB).
This value is also available as buffer.kMaxLength
.
buffer.constants.MAX_STRING_LENGTH
#
- <integer> The largest length allowed for a single
string
instance.
Represents the largest length
that a string
primitive can have, counted
in UTF-16 code units.
This value may depend on the JS engine that is being used.
Buffer.from()
, Buffer.alloc()
, and Buffer.allocUnsafe()
#
In versions of Node.js prior to 6.0.0, 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. Prior to Node.js 8.0.0, the memory allocated for suchBuffer
instances is not initialized and can contain sensitive data. SuchBuffer
instances must be subsequently initialized by using eitherbuf.fill(0)
or by writing to the entireBuffer
before reading data from theBuffer
. 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
. Since Node.js 8.0.0,Buffer(num)
andnew Buffer(num)
return aBuffer
with initialized memory. - 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()
is different depending on the type of the
first argument, security and reliability issues can be inadvertently introduced
into applications when argument validation or Buffer
initialization is not
performed.
For example, if an attacker can cause an application to receive a number where
a string is expected, the application may call new Buffer(100)
instead of new Buffer("100")
, leading it to allocate a 100 byte buffer instead
of allocating a 3 byte buffer with content "100"
. This is commonly possible
using JSON API calls. Since JSON distinguishes between numeric and string types,
it allows injection of numbers where a naively written application that does not
validate its input sufficiently might expect to always receive a string.
Before Node.js 8.0.0, the 100 byte buffer might contain
arbitrary pre-existing in-memory data, so may be used to expose in-memory
secrets to a remote attacker. Since Node.js 8.0.0, exposure of memory cannot
occur because the data is zero-filled. However, other attacks are still
possible, such as causing very large buffers to be allocated by the server,
leading to performance degradation or crashing on memory exhaustion.
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
that contains 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
that contains a copy of the contents of the givenBuffer
.Buffer.from(string[, encoding])
returns a newBuffer
that contains a copy of the provided string.Buffer.alloc(size[, fill[, encoding]])
returns a new initializedBuffer
of the specified size. This method is slower thanBuffer.allocUnsafe(size)
but guarantees that newly createdBuffer
instances never contain old data that is potentially sensitive. ATypeError
will be thrown ifsize
is not a number.Buffer.allocUnsafe(size)
andBuffer.allocUnsafeSlow(size)
each return a new uninitializedBuffer
of the specifiedsize
. Because theBuffer
is uninitialized, the allocated segment of memory might contain old data that is potentially sensitive.
Buffer
instances returned by Buffer.allocUnsafe()
and
Buffer.from(array)
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
cause all newly-allocated Buffer
instances to be zero-filled upon creation by
default. Without the option, buffers created with Buffer.allocUnsafe()
,
Buffer.allocUnsafeSlow()
, and new SlowBuffer(size)
are not zero-filled.
Use of this flag can have a measurable negative impact on performance. Use the
--zero-fill-buffers
option only when necessary to enforce that newly allocated
Buffer
instances cannot contain old data that is potentially sensitive.
$ 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.