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Node.js v7.5.1-nightly2017020113a024d531 Documentation
Table of Contents
- Buffer
Buffer.from()
,Buffer.alloc()
, andBuffer.allocUnsafe()
- Buffers and Character Encodings
- Buffers and TypedArray
- Buffers and ES6 iteration
- Class: Buffer
- new Buffer(array)
- new Buffer(buffer)
- new Buffer(arrayBuffer[, byteOffset [, length]])
- new Buffer(size)
- new Buffer(string[, encoding])
- Class Method: Buffer.alloc(size[, fill[, encoding]])
- Class Method: Buffer.allocUnsafe(size)
- Class Method: Buffer.allocUnsafeSlow(size)
- Class Method: Buffer.byteLength(string[, encoding])
- Class Method: Buffer.compare(buf1, buf2)
- Class Method: Buffer.concat(list[, totalLength])
- Class Method: Buffer.from(array)
- Class Method: Buffer.from(arrayBuffer[, byteOffset[, length]])
- Class Method: Buffer.from(buffer)
- Class Method: Buffer.from(string[, encoding])
- Class Method: Buffer.isBuffer(obj)
- Class Method: Buffer.isEncoding(encoding)
- Class Property: Buffer.poolSize
- buf[index]
- buf.compare(target[, targetStart[, targetEnd[, sourceStart[, sourceEnd]]]])
- buf.copy(target[, targetStart[, sourceStart[, sourceEnd]]])
- buf.entries()
- buf.equals(otherBuffer)
- buf.fill(value[, offset[, end]][, encoding])
- buf.indexOf(value[, byteOffset][, encoding])
- buf.includes(value[, byteOffset][, encoding])
- buf.keys()
- buf.lastIndexOf(value[, byteOffset][, encoding])
- buf.length
- buf.readDoubleBE(offset[, noAssert])
- buf.readDoubleLE(offset[, noAssert])
- buf.readFloatBE(offset[, noAssert])
- buf.readFloatLE(offset[, noAssert])
- buf.readInt8(offset[, noAssert])
- buf.readInt16BE(offset[, noAssert])
- buf.readInt16LE(offset[, noAssert])
- buf.readInt32BE(offset[, noAssert])
- buf.readInt32LE(offset[, noAssert])
- buf.readIntBE(offset, byteLength[, noAssert])
- buf.readIntLE(offset, byteLength[, noAssert])
- buf.readUInt8(offset[, noAssert])
- buf.readUInt16BE(offset[, noAssert])
- buf.readUInt16LE(offset[, noAssert])
- buf.readUInt32BE(offset[, noAssert])
- buf.readUInt32LE(offset[, noAssert])
- buf.readUIntBE(offset, byteLength[, noAssert])
- buf.readUIntLE(offset, byteLength[, noAssert])
- buf.slice([start[, end]])
- buf.swap16()
- buf.swap32()
- buf.swap64()
- buf.toString([encoding[, start[, end]]])
- buf.toJSON()
- buf.values()
- buf.write(string[, offset[, length]][, encoding])
- buf.writeDoubleBE(value, offset[, noAssert])
- buf.writeDoubleLE(value, offset[, noAssert])
- buf.writeFloatBE(value, offset[, noAssert])
- buf.writeFloatLE(value, offset[, noAssert])
- buf.writeInt8(value, offset[, noAssert])
- buf.writeInt16BE(value, offset[, noAssert])
- buf.writeInt16LE(value, offset[, noAssert])
- buf.writeInt32BE(value, offset[, noAssert])
- buf.writeInt32LE(value, offset[, noAssert])
- buf.writeIntBE(value, offset, byteLength[, noAssert])
- buf.writeIntLE(value, offset, byteLength[, noAssert])
- buf.writeUInt8(value, offset[, noAssert])
- buf.writeUInt16BE(value, offset[, noAssert])
- buf.writeUInt16LE(value, offset[, noAssert])
- buf.writeUInt32BE(value, offset[, noAssert])
- buf.writeUInt32LE(value, offset[, noAssert])
- buf.writeUIntBE(value, offset, byteLength[, noAssert])
- buf.writeUIntLE(value, offset, byteLength[, noAssert])
- buffer.INSPECT_MAX_BYTES
- buffer.kMaxLength
- buffer.transcode(source, fromEnc, toEnc)
- Class: SlowBuffer
Buffer#
Stability: 2 - Stable
Prior to the introduction of TypedArray
in ECMAScript 2015 (ES6), the
JavaScript language had no mechanism for reading or manipulating streams
of binary data. The Buffer
class was introduced as part of the Node.js
API to make it possible to interact with octet streams in the context of things
like TCP streams and file system operations.
Now that TypedArray
has been added in ES6, the Buffer
class implements the
Uint8Array
API in a manner that is more optimized and suitable for Node.js'
use cases.
Instances of the Buffer
class are similar to arrays of integers but
correspond to fixed-sized, raw memory allocations outside the V8 heap.
The size of the Buffer
is established when it is created and cannot be
resized.
The Buffer
class is a global within Node.js, making it unlikely that one
would need to ever use require('buffer').Buffer
.
Examples:
// Creates a zero-filled Buffer of length 10.
const buf1 = Buffer.alloc(10);
// Creates a Buffer of length 10, filled with 0x1.
const buf2 = Buffer.alloc(10, 1);
// Creates an uninitialized buffer of length 10.
// This is faster than calling Buffer.alloc() but the returned
// Buffer instance might contain old data that needs to be
// overwritten using either fill() or write().
const buf3 = Buffer.allocUnsafe(10);
// Creates a Buffer containing [0x1, 0x2, 0x3].
const buf4 = Buffer.from([1, 2, 3]);
// Creates a Buffer containing ASCII bytes [0x74, 0x65, 0x73, 0x74].
const buf5 = Buffer.from('test');
// Creates a Buffer containing UTF-8 bytes [0x74, 0xc3, 0xa9, 0x73, 0x74].
const buf6 = Buffer.from('tést', 'utf8');
Buffer.from()
, Buffer.alloc()
, and Buffer.allocUnsafe()
#
In versions of Node.js prior to v6, Buffer
instances were created using the
Buffer
constructor function, which allocates the returned Buffer
differently based on what arguments are provided:
- Passing a number as the first argument to
Buffer()
(e.g.new Buffer(10)
), allocates a newBuffer
object of the specified size. The memory allocated for suchBuffer
instances is not initialized and can contain sensitive data. SuchBuffer
instances must be initialized manually by using eitherbuf.fill(0)
or by writing to theBuffer
completely. While this behavior is intentional to improve performance, development experience has demonstrated that a more explicit distinction is required between creating a fast-but-uninitializedBuffer
versus creating a slower-but-saferBuffer
. - Passing a string, array, or
Buffer
as the first argument copies the passed object's data into theBuffer
. - Passing an
ArrayBuffer
returns aBuffer
that shares allocated memory with the givenArrayBuffer
.
Because the behavior of new Buffer()
changes significantly based on the type
of value passed as the first argument, applications that do not properly
validate the input arguments passed to new Buffer()
, or that fail to
appropriately initialize newly allocated Buffer
content, can inadvertently
introduce security and reliability issues into their code.
To make the creation of Buffer
instances more reliable and less error prone,
the various forms of the new Buffer()
constructor have been deprecated
and replaced by separate Buffer.from()
, Buffer.alloc()
, and
Buffer.allocUnsafe()
methods.
Developers should migrate all existing uses of the new Buffer()
constructors
to one of these new APIs.
Buffer.from(array)
returns a newBuffer
containing a copy of the provided octets.Buffer.from(arrayBuffer[, byteOffset [, length]])
returns a newBuffer
that shares the same allocated memory as the givenArrayBuffer
.Buffer.from(buffer)
returns a newBuffer
containing a copy of the contents of the givenBuffer
.Buffer.from(string[, encoding])
returns a newBuffer
containing a copy of the provided string.Buffer.alloc(size[, fill[, encoding]])
returns a "filled"Buffer
instance of the specified size. This method can be significantly slower thanBuffer.allocUnsafe(size)
but ensures that newly createdBuffer
instances never contain old and potentially sensitive data.Buffer.allocUnsafe(size)
andBuffer.allocUnsafeSlow(size)
each return a newBuffer
of the specifiedsize
whose content must be initialized using eitherbuf.fill(0)
or written to completely.
Buffer
instances returned by Buffer.allocUnsafe()
may be allocated off
a shared internal memory pool if size
is less than or equal to half
Buffer.poolSize
. Instances returned by Buffer.allocUnsafeSlow()
never
use the shared internal memory pool.
The --zero-fill-buffers
command line option#
Node.js can be started using the --zero-fill-buffers
command line option to
force all newly allocated Buffer
instances created using either
new Buffer(size)
, Buffer.allocUnsafe()
, Buffer.allocUnsafeSlow()
or
new SlowBuffer(size)
to be automatically zero-filled upon creation. Use of
this flag changes the default behavior of these methods and can have a significant
impact on performance. Use of the --zero-fill-buffers
option is recommended
only when necessary to enforce that newly allocated Buffer
instances cannot
contain potentially sensitive data.
Example:
$ node --zero-fill-buffers
> Buffer.allocUnsafe(5);
<Buffer 00 00 00 00 00>
What makes Buffer.allocUnsafe()
and Buffer.allocUnsafeSlow()
"unsafe"?#
When calling Buffer.allocUnsafe()
and Buffer.allocUnsafeSlow()
, the
segment of allocated memory is uninitialized (it is not zeroed-out). While
this design makes the allocation of memory quite fast, the allocated segment of
memory might contain old data that is potentially sensitive. Using a Buffer
created by Buffer.allocUnsafe()
without completely overwriting the memory
can allow this old data to be leaked when the Buffer
memory is read.
While there are clear performance advantages to using Buffer.allocUnsafe()
,
extra care must be taken in order to avoid introducing security
vulnerabilities into an application.
Buffers and Character Encodings#
Buffer
instances are commonly used to represent sequences of encoded characters
such as UTF-8, UCS2, Base64 or even Hex-encoded data. It is possible to
convert back and forth between Buffer
instances and ordinary JavaScript strings
by using an explicit character encoding.
Example:
const buf = Buffer.from('hello world', 'ascii');
// Prints: 68656c6c6f20776f726c64
console.log(buf.toString('hex'));
// Prints: aGVsbG8gd29ybGQ=
console.log(buf.toString('base64'));
The character encodings currently supported by Node.js include:
'ascii'
- for 7-bit ASCII data only. This encoding is fast and will strip the high bit if set.'utf8'
- Multibyte encoded Unicode characters. Many web pages and other document formats use UTF-8.'utf16le'
- 2 or 4 bytes, little-endian encoded Unicode characters. Surrogate pairs (U+10000 to U+10FFFF) are supported.'ucs2'
- Alias of'utf16le'
.'base64'
- Base64 encoding. When creating aBuffer
from a string, this encoding will also correctly accept "URL and Filename Safe Alphabet" as specified in RFC4648, Section 5.'latin1'
- A way of encoding theBuffer
into a one-byte encoded string (as defined by the IANA in RFC1345, page 63, to be the Latin-1 supplement block and C0/C1 control codes).'binary'
- Alias for'latin1'
.'hex'
- Encode each byte as two hexadecimal characters.
Note: Today's browsers follow the WHATWG spec which aliases both 'latin1' and
ISO-8859-1 to win-1252. This means that while doing something like http.get()
,
if the returned charset is one of those listed in the WHATWG spec it's possible
that the server actually returned win-1252-encoded data, and using 'latin1'
encoding may incorrectly decode the characters.
Buffers and TypedArray#
Buffer
instances are also Uint8Array
instances. However, there are subtle
incompatibilities with the TypedArray specification in ECMAScript 2015.
For example, while ArrayBuffer#slice()
creates a copy of the slice, the
implementation of Buffer#slice()
creates a view over the
existing Buffer
without copying, making Buffer#slice()
far
more efficient.
It is also possible to create new TypedArray
instances from a Buffer
with
the following caveats:
The
Buffer
object's memory is copied to theTypedArray
, not shared.The
Buffer
object's memory is interpreted as an array of distinct elements, and not as a byte array of the target type. That is,new Uint32Array(Buffer.from([1, 2, 3, 4]))
creates a 4-elementUint32Array
with elements[1, 2, 3, 4]
, not aUint32Array
with a single element[0x1020304]
or[0x4030201]
.
It is possible to create a new Buffer
that shares the same allocated memory as
a TypedArray
instance by using the TypeArray object's .buffer
property.
Example:
const arr = new Uint16Array(2);
arr[0] = 5000;
arr[1] = 4000;
// Copies the contents of `arr`
const buf1 = Buffer.from(arr);
// Shares memory with `arr`
const buf2 = Buffer.from(arr.buffer);
// Prints: <Buffer 88 a0>
console.log(buf1);
// Prints: <Buffer 88 13 a0 0f>
console.log(buf2);
arr[1] = 6000;
// Prints: <Buffer 88 a0>
console.log(buf1);
// Prints: <Buffer 88 13 70 17>
console.log(buf2);
Note that when creating a Buffer
using a TypedArray
's .buffer
, it is
possible to use only a portion of the underlying ArrayBuffer
by passing in
byteOffset
and length
parameters.
Example:
const arr = new Uint16Array(20);
const buf = Buffer.from(arr.buffer, 0, 16);
// Prints: 16
console.log(buf.length);
The Buffer.from()
and TypedArray.from()
have different signatures and
implementations. Specifically, the TypedArray
variants accept a second
argument that is a mapping function that is invoked on every element of the
typed array:
TypedArray.from(source[, mapFn[, thisArg]])
The Buffer.from()
method, however, does not support the use of a mapping
function:
Buffer.from(array)
Buffer.from(buffer)
Buffer.from(arrayBuffer[, byteOffset [, length]])
Buffer.from(string[, encoding])
Buffers and ES6 iteration#
Buffer
instances can be iterated over using the ECMAScript 2015 (ES6) for..of
syntax.
Example:
const buf = Buffer.from([1, 2, 3]);
// Prints:
// 1
// 2
// 3
for (const b of buf) {
console.log(b);
}
Additionally, the buf.values()
, buf.keys()
, and
buf.entries()
methods can be used to create iterators.
Class: Buffer#
The Buffer
class is a global type for dealing with binary data directly.
It can be constructed in a variety of ways.
new Buffer(array)#
Stability: 0 - Deprecated: Use Buffer.from(array)
instead.
array
<Array> An array of bytes to copy from
Allocates a new Buffer
using an array
of octets.
Example:
// Creates a new Buffer containing the ASCII bytes of the string 'buffer'
const buf = new Buffer([0x62, 0x75, 0x66, 0x66, 0x65, 0x72]);
new Buffer(buffer)#
Stability: 0 - Deprecated: Use Buffer.from(buffer)
instead.
buffer
<Buffer> An existingBuffer
to copy data from
Copies the passed buffer
data onto a new Buffer
instance.
Example:
const buf1 = new Buffer('buffer');
const buf2 = new Buffer(buf1);
buf1[0] = 0x61;
// Prints: auffer
console.log(buf1.toString());
// Prints: buffer
console.log(buf2.toString());
new Buffer(arrayBuffer[, byteOffset [, length]])#
Stability: 0 - Deprecated: Use
Buffer.from(arrayBuffer[, byteOffset [, length]])
instead.
arrayBuffer
<ArrayBuffer> AnArrayBuffer
or the.buffer
property of aTypedArray
.byteOffset
<Integer> Index of first byte to expose. Default:0
length
<Integer> Number of bytes to expose. Default:arrayBuffer.length - byteOffset
This creates a view of the ArrayBuffer
without copying the underlying
memory. For example, when passed a reference to the .buffer
property of a
TypedArray
instance, the newly created Buffer
will share the same
allocated memory as the TypedArray
.
The optional byteOffset
and length
arguments specify a memory range within
the arrayBuffer
that will be shared by the Buffer
.
Example:
const arr = new Uint16Array(2);
arr[0] = 5000;
arr[1] = 4000;
// Shares memory with `arr`
const buf = new Buffer(arr.buffer);
// Prints: <Buffer 88 13 a0 0f>
console.log(buf);
// Changing the original Uint16Array changes the Buffer also
arr[1] = 6000;
// Prints: <Buffer 88 13 70 17>
console.log(buf);
new Buffer(size)#
Stability: 0 - Deprecated: UseBuffer.alloc()
instead (also seeBuffer.allocUnsafe()
).
size
<Integer> The desired length of the newBuffer
Allocates a new Buffer
of size
bytes. If the size
is larger than
buffer.kMaxLength
or smaller than 0, a RangeError
will be thrown.
A zero-length Buffer
will be created if size
is 0.
Unlike ArrayBuffers
, the underlying memory for Buffer
instances
created in this way is not initialized. The contents of a newly created Buffer
are unknown and could contain sensitive data. Use
Buffer.alloc(size)
instead to initialize a Buffer
to zeroes.
Example:
const buf = new Buffer(10);
// Prints: (contents may vary): <Buffer 48 21 4b 00 00 00 00 00 30 dd>
console.log(buf);
buf.fill(0);
// Prints: <Buffer 00 00 00 00 00 00 00 00 00 00>
console.log(buf);
new Buffer(string[, encoding])#
Stability: 0 - Deprecated:
Use Buffer.from(string[, encoding])
instead.
Creates a new Buffer
containing the given JavaScript string string
. If
provided, the encoding
parameter identifies the character encoding of string
.
Examples:
const buf1 = new Buffer('this is a tést');
// Prints: this is a tést
console.log(buf1.toString());
// Prints: this is a tC)st
console.log(buf1.toString('ascii'));
const buf2 = new Buffer('7468697320697320612074c3a97374', 'hex');
// Prints: this is a tést
console.log(buf2.toString());
Class Method: Buffer.alloc(size[, fill[, encoding]])#
size
<Integer> The desired length of the newBuffer
fill
<String> | <Buffer> | <Integer> A value to pre-fill the newBuffer
with. Default:0
encoding
<String> Iffill
is a string, this is its encoding. Default:'utf8'
Allocates a new Buffer
of size
bytes. If fill
is undefined
, the
Buffer
will be zero-filled.
Example:
const buf = Buffer.alloc(5);
// Prints: <Buffer 00 00 00 00 00>
console.log(buf);
Allocates a new Buffer
of size
bytes. If the size
is larger than
buffer.kMaxLength
or smaller than 0, a RangeError
will be thrown.
A zero-length Buffer
will be created if size
is 0.
If fill
is specified, the allocated Buffer
will be initialized by calling
buf.fill(fill)
.
Example:
const buf = Buffer.alloc(5, 'a');
// Prints: <Buffer 61 61 61 61 61>
console.log(buf);
If both fill
and encoding
are specified, the allocated Buffer
will be
initialized by calling buf.fill(fill, encoding)
.
Example:
const buf = Buffer.alloc(11, 'aGVsbG8gd29ybGQ=', 'base64');
// Prints: <Buffer 68 65 6c 6c 6f 20 77 6f 72 6c 64>
console.log(buf);
Calling Buffer.alloc()
can be significantly slower than the alternative
Buffer.allocUnsafe()
but ensures that the newly created Buffer
instance
contents will never contain sensitive data.
A TypeError
will be thrown if size
is not a number.
Class Method: Buffer.allocUnsafe(size)#
size
<Integer> The desired length of the newBuffer
Allocates a new Buffer
of size
bytes. If the size
is larger than
buffer.kMaxLength
or smaller than 0, a RangeError
will be thrown.
A zero-length Buffer
will be 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 Buffer.alloc()
instead to initialize
Buffer
instances to zeroes.
Example:
const buf = Buffer.allocUnsafe(10);
// Prints: (contents may vary): <Buffer a0 8b 28 3f 01 00 00 00 50 32>
console.log(buf);
buf.fill(0);
// Prints: <Buffer 00 00 00 00 00 00 00 00 00 00>
console.log(buf);
A TypeError
will be thrown if size
is not a number.
Note that the Buffer
module pre-allocates an internal Buffer
instance of
size Buffer.poolSize
that is used as a pool for the fast allocation of new
Buffer
instances created using Buffer.allocUnsafe()
and the deprecated
new Buffer(size)
constructor only when size
is less than or equal to
Buffer.poolSize >> 1
(floor of Buffer.poolSize
divided by two).
Use of this pre-allocated internal memory pool is a key difference between
calling Buffer.alloc(size, fill)
vs. Buffer.allocUnsafe(size).fill(fill)
.
Specifically, Buffer.alloc(size, fill)
will never use the internal Buffer
pool, while Buffer.allocUnsafe(size).fill(fill)
will use the internal
Buffer
pool if size
is less than or equal to half Buffer.poolSize
. The
difference is subtle but can be important when an application requires the
additional performance that Buffer.allocUnsafe()
provides.
Class Method: Buffer.allocUnsafeSlow(size)#
size
<Integer> The desired length of the newBuffer
Allocates a new Buffer
of size
bytes. If the size
is larger than
buffer.kMaxLength
or smaller than 0, a RangeError
will be thrown.
A zero-length Buffer
will be 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 to zeroes.
When using Buffer.allocUnsafe()
to allocate new Buffer
instances,
allocations under 4KB are, by default, sliced from a single pre-allocated
Buffer
. This allows applications to avoid the garbage collection overhead of
creating many individually allocated Buffer
instances. This approach improves
both performance and memory usage by eliminating the need to track and cleanup as
many Persistent
objects.
However, in the case where a developer may need to retain a small chunk of
memory from a pool for an indeterminate amount of time, it may be appropriate
to create an un-pooled Buffer
instance using Buffer.allocUnsafeSlow()
then
copy out the relevant bits.
Example:
// Need to keep around a few small chunks of memory
const store = [];
socket.on('readable', () => {
const data = socket.read();
// Allocate for retained data
const sb = Buffer.allocUnsafeSlow(10);
// Copy the data into the new allocation
data.copy(sb, 0, 0, 10);
store.push(sb);
});
Use of Buffer.allocUnsafeSlow()
should be used only as a last resort after
a developer has observed undue memory retention in their applications.
A TypeError
will be thrown if size
is not a number.
Class Method: Buffer.byteLength(string[, encoding])#
string
<String> | <Buffer> | <TypedArray> | <DataView> | <ArrayBuffer> A value to calculate the length ofencoding
<String> Ifstring
is a string, this is its encoding. Default:'utf8'
- Returns: <Integer> The number of bytes contained within
string
Returns the actual byte length of a string. This is not the same as
String.prototype.length
since that returns the number of characters in
a string.
Example:
const str = '\u00bd + \u00bc = \u00be';
// Prints: ½ + ¼ = ¾: 9 characters, 12 bytes
console.log(`${str}: ${str.length} characters, ` +
`${Buffer.byteLength(str, 'utf8')} bytes`);
When string
is a Buffer
/DataView
/TypedArray
/ArrayBuffer
, the
actual byte length is returned.
Class Method: Buffer.compare(buf1, buf2)#
Compares buf1
to buf2
typically for the purpose of sorting arrays of
Buffer
instances. This is equivalent to calling
buf1.compare(buf2)
.
Example:
const buf1 = Buffer.from('1234');
const buf2 = Buffer.from('0123');
const arr = [buf1, buf2];
// Prints: [ <Buffer 30 31 32 33>, <Buffer 31 32 33 34> ]
// (This result is equal to: [buf2, buf1])
console.log(arr.sort(Buffer.compare));
Class Method: Buffer.concat(list[, totalLength])#
list
<Array> List ofBuffer
instances to concattotalLength
<Integer> Total length of theBuffer
instances inlist
when concatenated- Returns: <Buffer>
Returns a new Buffer
which is the result of concatenating all the Buffer
instances in the list
together.
If the list has no items, or if the totalLength
is 0, then a new zero-length
Buffer
is returned.
If totalLength
is not provided, it is calculated from the Buffer
instances
in list
. This however causes an additional loop to be executed in order to
calculate the totalLength
, so it is faster to provide the length explicitly if
it is already known.
Example: Create a single Buffer
from a list of three Buffer
instances
const buf1 = Buffer.alloc(10);
const buf2 = Buffer.alloc(14);
const buf3 = Buffer.alloc(18);
const totalLength = buf1.length + buf2.length + buf3.length;
// Prints: 42
console.log(totalLength);
const bufA = Buffer.concat([buf1, buf2, buf3], totalLength);
// Prints: <Buffer 00 00 00 00 ...>
console.log(bufA);
// Prints: 42
console.log(bufA.length);
Class Method: Buffer.from(array)#
array
<Array>
Allocates a new Buffer
using an array
of octets.
Example:
// Creates a new Buffer containing ASCII bytes of the string 'buffer'
const buf = Buffer.from([0x62, 0x75, 0x66, 0x66, 0x65, 0x72]);
A TypeError
will be thrown if array
is not an Array
.
Class Method: Buffer.from(arrayBuffer[, byteOffset[, length]])#
arrayBuffer
<ArrayBuffer> AnArrayBuffer
or the.buffer
property of aTypedArray
.byteOffset
<Integer> Index of first byte to expose. Default:0
length
<Integer> Number of bytes to expose. Default:arrayBuffer.length - byteOffset
This creates a view of the ArrayBuffer
without copying the underlying
memory. For example, when passed a reference to the .buffer
property of a
TypedArray
instance, the newly created Buffer
will share the same
allocated memory as the TypedArray
.
Example:
const arr = new Uint16Array(2);
arr[0] = 5000;
arr[1] = 4000;
// Shares memory with `arr`
const buf = Buffer.from(arr.buffer);
// Prints: <Buffer 88 13 a0 0f>
console.log(buf);
// Changing the original Uint16Array changes the Buffer also
arr[1] = 6000;
// Prints: <Buffer 88 13 70 17>
console.log(buf);
The optional byteOffset
and length
arguments specify a memory range within
the arrayBuffer
that will be shared by the Buffer
.
Example:
const ab = new ArrayBuffer(10);
const buf = Buffer.from(ab, 0, 2);
// Prints: 2
console.log(buf.length);
A TypeError
will be thrown if arrayBuffer
is not an ArrayBuffer
.
Class Method: Buffer.from(buffer)#
buffer
<Buffer> An existingBuffer
to copy data from
Copies the passed buffer
data onto a new Buffer
instance.
Example:
const buf1 = Buffer.from('buffer');
const buf2 = Buffer.from(buf1);
buf1[0] = 0x61;
// Prints: auffer
console.log(buf1.toString());
// Prints: buffer
console.log(buf2.toString());
A TypeError
will be thrown if buffer
is not a Buffer
.
Class Method: Buffer.from(string[, encoding])#
Creates a new Buffer
containing the given JavaScript string string
. If
provided, the encoding
parameter identifies the character encoding of string
.
Examples:
const buf1 = Buffer.from('this is a tést');
// Prints: this is a tést
console.log(buf1.toString());
// Prints: this is a tC)st
console.log(buf1.toString('ascii'));
const buf2 = Buffer.from('7468697320697320612074c3a97374', 'hex');
// Prints: this is a tést
console.log(buf2.toString());
A TypeError
will be thrown if str
is not a string.
Class Method: Buffer.isBuffer(obj)#
Returns true
if obj
is a Buffer
, false
otherwise.
Class Method: Buffer.isEncoding(encoding)#
Returns true
if encoding
contains a supported character encoding, or false
otherwise.
Class Property: Buffer.poolSize#
- <Integer> Default:
8192
This is the number of bytes used to determine the size of pre-allocated, internal
Buffer
instances used for pooling. This value may be modified.
buf[index]#
The index operator [index]
can be used to get and set the octet at position
index
in buf
. The values refer to individual bytes, so the legal value
range is between 0x00
and 0xFF
(hex) or 0
and 255
(decimal).
Example: Copy an ASCII string into a Buffer
, one byte at a time
const str = 'Node.js';
const buf = Buffer.allocUnsafe(str.length);
for (let i = 0; i < str.length ; i++) {
buf[i] = str.charCodeAt(i);
}
// Prints: Node.js
console.log(buf.toString('ascii'));
buf.compare(target[, targetStart[, targetEnd[, sourceStart[, sourceEnd]]]])#
target
<Buffer> ABuffer
to compare totargetStart
<Integer> The offset withintarget
at which to begin comparison. Default:0
targetEnd
<Integer> The offset withtarget
at which to end comparison (not inclusive). Ignored whentargetStart
isundefined
. Default:target.length
sourceStart
<Integer> The offset withinbuf
at which to begin comparison. Ignored whentargetStart
isundefined
. Default:0
sourceEnd
<Integer> The offset withinbuf
at which to end comparison (not inclusive). Ignored whentargetStart
isundefined
. Default:buf.length
- Returns: <Integer>
Compares buf
with target
and returns a number indicating whether buf
comes before, after, or is the same as target
in sort order.
Comparison is based on the actual sequence of bytes in each Buffer
.
0
is returned iftarget
is the same asbuf
1
is returned iftarget
should come beforebuf
when sorted.-1
is returned iftarget
should come afterbuf
when sorted.
Examples:
const buf1 = Buffer.from('ABC');
const buf2 = Buffer.from('BCD');
const buf3 = Buffer.from('ABCD');
// Prints: 0
console.log(buf1.compare(buf1));
// Prints: -1
console.log(buf1.compare(buf2));
// Prints: -1
console.log(buf1.compare(buf3));
// Prints: 1
console.log(buf2.compare(buf1));
// Prints: 1
console.log(buf2.compare(buf3));
// Prints: [ <Buffer 41 42 43>, <Buffer 41 42 43 44>, <Buffer 42 43 44> ]
// (This result is equal to: [buf1, buf3, buf2])
console.log([buf1, buf2, buf3].sort(Buffer.compare));
The optional targetStart
, targetEnd
, sourceStart
, and sourceEnd
arguments can be used to limit the comparison to specific ranges within target
and buf
respectively.
Examples:
const buf1 = Buffer.from([1, 2, 3, 4, 5, 6, 7, 8, 9]);
const buf2 = Buffer.from([5, 6, 7, 8, 9, 1, 2, 3, 4]);
// Prints: 0
console.log(buf1.compare(buf2, 5, 9, 0, 4));
// Prints: -1
console.log(buf1.compare(buf2, 0, 6, 4));
// Prints: 1
console.log(buf1.compare(buf2, 5, 6, 5));
A RangeError
will be thrown if: targetStart < 0
, sourceStart < 0
,
targetEnd > target.byteLength
or sourceEnd > source.byteLength
.
buf.copy(target[, targetStart[, sourceStart[, sourceEnd]]])#
target
<Buffer> ABuffer
to copy into.targetStart
<Integer> The offset withintarget
at which to begin copying to. Default:0
sourceStart
<Integer> The offset withinbuf
at which to begin copying from. Ignored whentargetStart
isundefined
. Default:0
sourceEnd
<Integer> The offset withinbuf
at which to stop copying (not inclusive). Ignored whensourceStart
isundefined
. Default:buf.length
- Returns: <Integer> The number of bytes copied.
Copies data from a region of buf
to a region in target
even if the target
memory region overlaps with buf
.
Example: Create two Buffer
instances, buf1
and buf2
, and copy buf1
from
byte 16 through byte 19 into buf2
, starting at the 8th byte in buf2
const buf1 = Buffer.allocUnsafe(26);
const buf2 = Buffer.allocUnsafe(26).fill('!');
for (let i = 0 ; i < 26 ; i++) {
// 97 is the decimal ASCII value for 'a'
buf1[i] = i + 97;
}
buf1.copy(buf2, 8, 16, 20);
// Prints: !!!!!!!!qrst!!!!!!!!!!!!!
console.log(buf2.toString('ascii', 0, 25));
Example: Create a single Buffer
and copy data from one region to an
overlapping region within the same Buffer
const buf = Buffer.allocUnsafe(26);
for (let i = 0 ; i < 26 ; i++) {
// 97 is the decimal ASCII value for 'a'
buf[i] = i + 97;
}
buf.copy(buf, 0, 4, 10);
// Prints: efghijghijklmnopqrstuvwxyz
console.log(buf.toString());
buf.entries()#
- Returns: <Iterator>
Creates and returns an iterator of [index, byte]
pairs from the contents of
buf
.
Example: Log the entire contents of a Buffer
const buf = Buffer.from('buffer');
// Prints:
// [0, 98]
// [1, 117]
// [2, 102]
// [3, 102]
// [4, 101]
// [5, 114]
for (const pair of buf.entries()) {
console.log(pair);
}
buf.equals(otherBuffer)#
Returns true
if both buf
and otherBuffer
have exactly the same bytes,
false
otherwise.
Examples:
const buf1 = Buffer.from('ABC');
const buf2 = Buffer.from('414243', 'hex');
const buf3 = Buffer.from('ABCD');
// Prints: true
console.log(buf1.equals(buf2));
// Prints: false
console.log(buf1.equals(buf3));
buf.fill(value[, offset[, end]][, encoding])#
value
<String> | <Buffer> | <Integer> The value to fillbuf
withoffset
<Integer> Where to start fillingbuf
. Default:0
end
<Integer> Where to stop fillingbuf
(not inclusive). Default:buf.length
encoding
<String> Ifvalue
is a string, this is its encoding. Default:'utf8'
- Returns: <Buffer> A reference to
buf
Fills buf
with the specified value
. If the offset
and end
are not given,
the entire buf
will be filled. This is meant to be a small simplification to
allow the creation and filling of a Buffer
to be done on a single line.
Example: Fill a Buffer
with the ASCII character 'h'
const b = Buffer.allocUnsafe(50).fill('h');
// Prints: hhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh
console.log(b.toString());
value
is coerced to a uint32
value if it is not a String or Integer.
If the final write of a fill()
operation falls on a multi-byte character,
then only the first bytes of that character that fit into buf
are written.
Example: Fill a Buffer
with a two-byte character
// Prints: <Buffer c8 a2 c8>
console.log(Buffer.allocUnsafe(3).fill('\u0222'));
buf.indexOf(value[, byteOffset][, encoding])#
value
<String> | <Buffer> | <Integer> What to search forbyteOffset
<Integer> Where to begin searching inbuf
. Default:0
encoding
<String> Ifvalue
is a string, this is its encoding. Default:'utf8'
- Returns: <Integer> The index of the first occurrence of
value
inbuf
or-1
ifbuf
does not containvalue
If value
is:
- a string,
value
is interpreted according to the character encoding inencoding
. - a
Buffer
,value
will be used in its entirety. To compare a partialBuffer
usebuf.slice()
. - a number,
value
will be interpreted as an unsigned 8-bit integer value between0
and255
.
Examples:
const buf = Buffer.from('this is a buffer');
// Prints: 0
console.log(buf.indexOf('this'));
// Prints: 2
console.log(buf.indexOf('is'));
// Prints: 8
console.log(buf.indexOf(Buffer.from('a buffer')));
// Prints: 8
// (97 is the decimal ASCII value for 'a')
console.log(buf.indexOf(97));
// Prints: -1
console.log(buf.indexOf(Buffer.from('a buffer example')));
// Prints: 8
console.log(buf.indexOf(Buffer.from('a buffer example').slice(0, 8)));
const utf16Buffer = Buffer.from('\u039a\u0391\u03a3\u03a3\u0395', 'ucs2');
// Prints: 4
console.log(utf16Buffer.indexOf('\u03a3', 0, 'ucs2'));
// Prints: 6
console.log(utf16Buffer.indexOf('\u03a3', -4, 'ucs2'));
If value
is not a string, number, or Buffer
, this method will throw a
TypeError
. If value
is a number, it will be coerced to a valid byte value,
an integer between 0 and 255.
If byteOffset
is not a number, it will be coerced to a number. Any arguments
that coerce to NaN
or 0, like {}
, []
, null
or undefined
, will search
the whole buffer. This behavior matches String#indexOf()
.
const b = Buffer.from('abcdef');
// Passing a value that's a number, but not a valid byte
// Prints: 2, equivalent to searching for 99 or 'c'
console.log(b.indexOf(99.9));
console.log(b.indexOf(256 + 99));
// Passing a byteOffset that coerces to NaN or 0
// Prints: 1, searching the whole buffer
console.log(b.indexOf('b', undefined));
console.log(b.indexOf('b', {}));
console.log(b.indexOf('b', null));
console.log(b.indexOf('b', []));
buf.includes(value[, byteOffset][, encoding])#
value
<String> | <Buffer> | <Integer> What to search forbyteOffset
<Integer> Where to begin searching inbuf
. Default:0
encoding
<String> Ifvalue
is a string, this is its encoding. Default:'utf8'
- Returns: <Boolean>
true
ifvalue
was found inbuf
,false
otherwise
Equivalent to buf.indexOf() !== -1
.
Examples:
const buf = Buffer.from('this is a buffer');
// Prints: true
console.log(buf.includes('this'));
// Prints: true
console.log(buf.includes('is'));
// Prints: true
console.log(buf.includes(Buffer.from('a buffer')));
// Prints: true
// (97 is the decimal ASCII value for 'a')
console.log(buf.includes(97));
// Prints: false
console.log(buf.includes(Buffer.from('a buffer example')));
// Prints: true
console.log(buf.includes(Buffer.from('a buffer example').slice(0, 8)));
// Prints: false
console.log(buf.includes('this', 4));
buf.keys()#
- Returns: <Iterator>
Creates and returns an iterator of buf
keys (indices).
Example:
const buf = Buffer.from('buffer');
// Prints:
// 0
// 1
// 2
// 3
// 4
// 5
for (const key of buf.keys()) {
console.log(key);
}
buf.lastIndexOf(value[, byteOffset][, encoding])#
value
<String> | <Buffer> | <Integer> What to search forbyteOffset
<Integer> Where to begin searching inbuf
. Default:buf.length
- 1
encoding
<String> Ifvalue
is a string, this is its encoding. Default:'utf8'
- Returns: <Integer> The index of the last occurrence of
value
inbuf
or-1
ifbuf
does not containvalue
Identical to buf.indexOf()
, except buf
is searched from back to front
instead of front to back.
Examples:
const buf = Buffer.from('this buffer is a buffer');
// Prints: 0
console.log(buf.lastIndexOf('this'));
// Prints: 17
console.log(buf.lastIndexOf('buffer'));
// Prints: 17
console.log(buf.lastIndexOf(Buffer.from('buffer')));
// Prints: 15
// (97 is the decimal ASCII value for 'a')
console.log(buf.lastIndexOf(97));
// Prints: -1
console.log(buf.lastIndexOf(Buffer.from('yolo')));
// Prints: 5
console.log(buf.lastIndexOf('buffer', 5));
// Prints: -1
console.log(buf.lastIndexOf('buffer', 4));
const utf16Buffer = Buffer.from('\u039a\u0391\u03a3\u03a3\u0395', 'ucs2');
// Prints: 6
console.log(utf16Buffer.lastIndexOf('\u03a3', undefined, 'ucs2'));
// Prints: 4
console.log(utf16Buffer.lastIndexOf('\u03a3', -5, 'ucs2'));
If value
is not a string, number, or Buffer
, this method will throw a
TypeError
. If value
is a number, it will be coerced to a valid byte value,
an integer between 0 and 255.
If byteOffset
is not a number, it will be coerced to a number. Any arguments
that coerce to NaN
, like {}
or undefined
, will search the whole buffer.
This behavior matches String#lastIndexOf()
.
const b = Buffer.from('abcdef');
// Passing a value that's a number, but not a valid byte
// Prints: 2, equivalent to searching for 99 or 'c'
console.log(b.lastIndexOf(99.9));
console.log(b.lastIndexOf(256 + 99));
// Passing a byteOffset that coerces to NaN
// Prints: 1, searching the whole buffer
console.log(b.lastIndexOf('b', undefined));
console.log(b.lastIndexOf('b', {}));
// Passing a byteOffset that coerces to 0
// Prints: -1, equivalent to passing 0
console.log(b.lastIndexOf('b', null));
console.log(b.lastIndexOf('b', []));
buf.length#
Returns the amount of memory allocated for buf
in bytes. Note that this
does not necessarily reflect the amount of "usable" data within buf
.
Example: Create a Buffer
and write a shorter ASCII string to it
const buf = Buffer.alloc(1234);
// Prints: 1234
console.log(buf.length);
buf.write('some string', 0, 'ascii');
// Prints: 1234
console.log(buf.length);
While the length
property is not immutable, changing the value of length
can result in undefined and inconsistent behavior. Applications that wish to
modify the length of a Buffer
should therefore treat length
as read-only and
use buf.slice()
to create a new Buffer
.
Examples:
let buf = Buffer.allocUnsafe(10);
buf.write('abcdefghj', 0, 'ascii');
// Prints: 10
console.log(buf.length);
buf = buf.slice(0, 5);
// Prints: 5
console.log(buf.length);
buf.readDoubleBE(offset[, noAssert])#
buf.readDoubleLE(offset[, noAssert])#
offset
<Integer> Where to start reading. Must satisfy:0 <= offset <= buf.length - 8
noAssert
<Boolean> Skipoffset
validation? Default:false
- Returns: <Number>
Reads a 64-bit double from buf
at the specified offset
with specified
endian format (readDoubleBE()
returns big endian, readDoubleLE()
returns
little endian).
Setting noAssert
to true
allows offset
to be beyond the end of buf
, but
the result should be considered undefined behavior.
Examples:
const buf = Buffer.from([1, 2, 3, 4, 5, 6, 7, 8]);
// Prints: 8.20788039913184e-304
console.log(buf.readDoubleBE());
// Prints: 5.447603722011605e-270
console.log(buf.readDoubleLE());
// Throws an exception: RangeError: Index out of range
console.log(buf.readDoubleLE(1));
// Warning: reads passed end of buffer!
// This will result in a segmentation fault! Don't do this!
console.log(buf.readDoubleLE(1, true));
buf.readFloatBE(offset[, noAssert])#
buf.readFloatLE(offset[, noAssert])#
offset
<Integer> Where to start reading. Must satisfy:0 <= offset <= buf.length - 4
noAssert
<Boolean> Skipoffset
validation? Default:false
- Returns: <Number>
Reads a 32-bit float from buf
at the specified offset
with specified
endian format (readFloatBE()
returns big endian, readFloatLE()
returns
little endian).
Setting noAssert
to true
allows offset
to be beyond the end of buf
, but
the result should be considered undefined behavior.
Examples:
const buf = Buffer.from([1, 2, 3, 4]);
// Prints: 2.387939260590663e-38
console.log(buf.readFloatBE());
// Prints: 1.539989614439558e-36
console.log(buf.readFloatLE());
// Throws an exception: RangeError: Index out of range
console.log(buf.readFloatLE(1));
// Warning: reads passed end of buffer!
// This will result in a segmentation fault! Don't do this!
console.log(buf.readFloatLE(1, true));
buf.readInt8(offset[, noAssert])#
offset
<Integer> Where to start reading. Must satisfy:0 <= offset <= buf.length - 1
noAssert
<Boolean> Skipoffset
validation? Default:false
- Returns: <Integer>
Reads a signed 8-bit integer from buf
at the specified offset
.
Setting noAssert
to true
allows offset
to be beyond the end of buf
, but
the result should be considered undefined behavior.
Integers read from a Buffer
are interpreted as two's complement signed values.
Examples:
const buf = Buffer.from([-1, 5]);
// Prints: -1
console.log(buf.readInt8(0));
// Prints: 5
console.log(buf.readInt8(1));
// Throws an exception: RangeError: Index out of range
console.log(buf.readInt8(2));
buf.readInt16BE(offset[, noAssert])#
buf.readInt16LE(offset[, noAssert])#
offset
<Integer> Where to start reading. Must satisfy:0 <= offset <= buf.length - 2
noAssert
<Boolean> Skipoffset
validation? Default:false
- Returns: <Integer>
Reads a signed 16-bit integer from buf
at the specified offset
with
the specified endian format (readInt16BE()
returns big endian,
readInt16LE()
returns little endian).
Setting noAssert
to true
allows offset
to be beyond the end of buf
, but
the result should be considered undefined behavior.
Integers read from a Buffer
are interpreted as two's complement signed values.
Examples:
const buf = Buffer.from([0, 5]);
// Prints: 5
console.log(buf.readInt16BE());
// Prints: 1280
console.log(buf.readInt16LE());
// Throws an exception: RangeError: Index out of range
console.log(buf.readInt16LE(1));
buf.readInt32BE(offset[, noAssert])#
buf.readInt32LE(offset[, noAssert])#
offset
<Integer> Where to start reading. Must satisfy:0 <= offset <= buf.length - 4
noAssert
<Boolean> Skipoffset
validation? Default:false
- Returns: <Integer>
Reads a signed 32-bit integer from buf
at the specified offset
with
the specified endian format (readInt32BE()
returns big endian,
readInt32LE()
returns little endian).
Setting noAssert
to true
allows offset
to be beyond the end of buf
, but
the result should be considered undefined behavior.
Integers read from a Buffer
are interpreted as two's complement signed values.
Examples:
const buf = Buffer.from([0, 0, 0, 5]);
// Prints: 5
console.log(buf.readInt32BE());
// Prints: 83886080
console.log(buf.readInt32LE());
// Throws an exception: RangeError: Index out of range
console.log(buf.readInt32LE(1));
buf.readIntBE(offset, byteLength[, noAssert])#
buf.readIntLE(offset, byteLength[, noAssert])#
offset
<Integer> Where to start reading. Must satisfy:0 <= offset <= buf.length - byteLength
byteLength
<Integer> How many bytes to read. Must satisfy:0 < byteLength <= 6
noAssert
<Boolean> Skipoffset
andbyteLength
validation? Default:false
- Returns: <Integer>
Reads byteLength
number of bytes from buf
at the specified offset
and interprets the result as a two's complement signed value. Supports up to 48
bits of accuracy.
Setting noAssert
to true
allows offset
to be beyond the end of buf
, but
the result should be considered undefined behavior.
Examples:
const buf = Buffer.from([0x12, 0x34, 0x56, 0x78, 0x90, 0xab]);
// Prints: -546f87a9cbee
console.log(buf.readIntLE(0, 6).toString(16));
// Prints: 1234567890ab
console.log(buf.readIntBE(0, 6).toString(16));
// Throws an exception: RangeError: Index out of range
console.log(buf.readIntBE(1, 6).toString(16));
buf.readUInt8(offset[, noAssert])#
offset
<Integer> Where to start reading. Must satisfy:0 <= offset <= buf.length - 1
noAssert
<Boolean> Skipoffset
validation? Default:false
- Returns: <Integer>
Reads an unsigned 8-bit integer from buf
at the specified offset
.
Setting noAssert
to true
allows offset
to be beyond the end of buf
, but
the result should be considered undefined behavior.
Examples:
const buf = Buffer.from([1, -2]);
// Prints: 1
console.log(buf.readUInt8(0));
// Prints: 254
console.log(buf.readUInt8(1));
// Throws an exception: RangeError: Index out of range
console.log(buf.readUInt8(2));
buf.readUInt16BE(offset[, noAssert])#
buf.readUInt16LE(offset[, noAssert])#
offset
<Integer> Where to start reading. Must satisfy:0 <= offset <= buf.length - 2
noAssert
<Boolean> Skipoffset
validation? Default:false
- Returns: <Integer>
Reads an unsigned 16-bit integer from buf
at the specified offset
with
specified endian format (readUInt16BE()
returns big endian, readUInt16LE()
returns little endian).
Setting noAssert
to true
allows offset
to be beyond the end of buf
, but
the result should be considered undefined behavior.
Examples:
const buf = Buffer.from([0x12, 0x34, 0x56]);
// Prints: 1234
console.log(buf.readUInt16BE(0).toString(16));
// Prints: 3412
console.log(buf.readUInt16LE(0).toString(16));
// Prints: 3456
console.log(buf.readUInt16BE(1).toString(16));
// Prints: 5634
console.log(buf.readUInt16LE(1).toString(16));
// Throws an exception: RangeError: Index out of range
console.log(buf.readUInt16LE(2).toString(16));
buf.readUInt32BE(offset[, noAssert])#
buf.readUInt32LE(offset[, noAssert])#
offset
<Integer> Where to start reading. Must satisfy:0 <= offset <= buf.length - 4
noAssert
<Boolean> Skipoffset
validation? Default:false
- Returns: <Integer>
Reads an unsigned 32-bit integer from buf
at the specified offset
with
specified endian format (readUInt32BE()
returns big endian,
readUInt32LE()
returns little endian).
Setting noAssert
to true
allows offset
to be beyond the end of buf
, but
the result should be considered undefined behavior.
Examples:
const buf = Buffer.from([0x12, 0x34, 0x56, 0x78]);
// Prints: 12345678
console.log(buf.readUInt32BE(0).toString(16));
// Prints: 78563412
console.log(buf.readUInt32LE(0).toString(16));
// Throws an exception: RangeError: Index out of range
console.log(buf.readUInt32LE(1).toString(16));
buf.readUIntBE(offset, byteLength[, noAssert])#
buf.readUIntLE(offset, byteLength[, noAssert])#
offset
<Integer> Where to start reading. Must satisfy:0 <= offset <= buf.length - byteLength
byteLength
<Integer> How many bytes to read. Must satisfy:0 < byteLength <= 6
noAssert
<Boolean> Skipoffset
andbyteLength
validation? Default:false
- Returns: <Integer>
Reads byteLength
number of bytes from buf
at the specified offset
and interprets the result as an unsigned integer. Supports up to 48
bits of accuracy.
Setting noAssert
to true
allows offset
to be beyond the end of buf
, but
the result should be considered undefined behavior.
Examples:
const buf = Buffer.from([0x12, 0x34, 0x56, 0x78, 0x90, 0xab]);
// Prints: 1234567890ab
console.log(buf.readUIntBE(0, 6).toString(16));
// Prints: ab9078563412
console.log(buf.readUIntLE(0, 6).toString(16));
// Throws an exception: RangeError: Index out of range
console.log(buf.readUIntBE(1, 6).toString(16));
buf.slice([start[, end]])#
start
<Integer> Where the newBuffer
will start. Default:0
end
<Integer> Where the newBuffer
will end (not inclusive). Default:buf.length
- Returns: <Buffer>
Returns a new Buffer
that references the same memory as the original, but
offset and cropped by the start
and end
indices.
Note that modifying the new Buffer
slice will modify the memory in the
original Buffer
because the allocated memory of the two objects overlap.
Example: Create a Buffer
with the ASCII alphabet, take a slice, and then modify
one byte from the original Buffer
const buf1 = Buffer.allocUnsafe(26);
for (let i = 0 ; i < 26 ; i++) {
// 97 is the decimal ASCII value for 'a'
buf1[i] = i + 97;
}
const buf2 = buf1.slice(0, 3);
// Prints: abc
console.log(buf2.toString('ascii', 0, buf2.length));
buf1[0] = 33;
// Prints: !bc
console.log(buf2.toString('ascii', 0, buf2.length));
Specifying negative indexes causes the slice to be generated relative to the
end of buf
rather than the beginning.
Examples:
const buf = Buffer.from('buffer');
// Prints: buffe
// (Equivalent to buf.slice(0, 5))
console.log(buf.slice(-6, -1).toString());
// Prints: buff
// (Equivalent to buf.slice(0, 4))
console.log(buf.slice(-6, -2).toString());
// Prints: uff
// (Equivalent to buf.slice(1, 4))
console.log(buf.slice(-5, -2).toString());
buf.swap16()#
- Returns: <Buffer> A reference to
buf
Interprets buf
as an array of unsigned 16-bit integers and swaps the byte-order
in-place. Throws a RangeError
if buf.length
is not a multiple of 2.
Examples:
const buf1 = Buffer.from([0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8]);
// Prints: <Buffer 01 02 03 04 05 06 07 08>
console.log(buf1);
buf1.swap16();
// Prints: <Buffer 02 01 04 03 06 05 08 07>
console.log(buf1);
const buf2 = Buffer.from([0x1, 0x2, 0x3]);
// Throws an exception: RangeError: Buffer size must be a multiple of 16-bits
buf2.swap16();
buf.swap32()#
- Returns: <Buffer> A reference to
buf
Interprets buf
as an array of unsigned 32-bit integers and swaps the byte-order
in-place. Throws a RangeError
if buf.length
is not a multiple of 4.
Examples:
const buf1 = Buffer.from([0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8]);
// Prints: <Buffer 01 02 03 04 05 06 07 08>
console.log(buf1);
buf1.swap32();
// Prints: <Buffer 04 03 02 01 08 07 06 05>
console.log(buf1);
const buf2 = Buffer.from([0x1, 0x2, 0x3]);
// Throws an exception: RangeError: Buffer size must be a multiple of 32-bits
buf2.swap32();
buf.swap64()#
- Returns: <Buffer> A reference to
buf
Interprets buf
as an array of 64-bit numbers and swaps the byte-order in-place.
Throws a RangeError
if buf.length
is not a multiple of 8.
Examples:
const buf1 = Buffer.from([0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8]);
// Prints: <Buffer 01 02 03 04 05 06 07 08>
console.log(buf1);
buf1.swap64();
// Prints: <Buffer 08 07 06 05 04 03 02 01>
console.log(buf1);
const buf2 = Buffer.from([0x1, 0x2, 0x3]);
// Throws an exception: RangeError: Buffer size must be a multiple of 64-bits
buf2.swap64();
Note that JavaScript cannot encode 64-bit integers. This method is intended for working with 64-bit floats.
buf.toString([encoding[, start[, end]]])#
encoding
<String> The character encoding to decode to. Default:'utf8'
start
<Integer> The byte offset to start decoding at. Default:0
end
<Integer> The byte offset to stop decoding at (not inclusive). Default:buf.length
- Returns: <String>
Decodes buf
to a string according to the specified character encoding in
encoding
. start
and end
may be passed to decode only a subset of buf
.
Examples:
const buf1 = Buffer.allocUnsafe(26);
for (let i = 0 ; i < 26 ; i++) {
// 97 is the decimal ASCII value for 'a'
buf1[i] = i + 97;
}
// Prints: abcdefghijklmnopqrstuvwxyz
console.log(buf1.toString('ascii'));
// Prints: abcde
console.log(buf1.toString('ascii', 0, 5));
const buf2 = Buffer.from('tést');
// Prints: 74c3a97374
console.log(buf2.toString('hex'));
// Prints: té
console.log(buf2.toString('utf8', 0, 3));
// Prints: té
console.log(buf2.toString(undefined, 0, 3));
buf.toJSON()#
- Returns: <Object>
Returns a JSON representation of buf
. JSON.stringify()
implicitly calls
this function when stringifying a Buffer
instance.
Example:
const buf = Buffer.from([0x1, 0x2, 0x3, 0x4, 0x5]);
const json = JSON.stringify(buf);
// Prints: {"type":"Buffer","data":[1,2,3,4,5]}
console.log(json);
const copy = JSON.parse(json, (key, value) => {
return value && value.type === 'Buffer'
? Buffer.from(value.data)
: value;
});
// Prints: <Buffer 01 02 03 04 05>
console.log(copy);
buf.values()#
- Returns: <Iterator>
Creates and returns an iterator for buf
values (bytes). This function is
called automatically when a Buffer
is used in a for..of
statement.
Examples:
const buf = Buffer.from('buffer');
// Prints:
// 98
// 117
// 102
// 102
// 101
// 114
for (const value of buf.values()) {
console.log(value);
}
// Prints:
// 98
// 117
// 102
// 102
// 101
// 114
for (const value of buf) {
console.log(value);
}
buf.write(string[, offset[, length]][, encoding])#
string
<String> String to be written tobuf
offset
<Integer> Where to start writingstring
. Default:0
length
<Integer> How many bytes to write. Default:buf.length - offset
encoding
<String> The character encoding ofstring
. Default:'utf8'
- Returns: <Integer> Number of bytes written
Writes string
to buf
at offset
according to the character encoding in encoding
.
The length
parameter is the number of bytes to write. If buf
did not contain
enough space to fit the entire string, only a partial amount of string
will
be written. However, partially encoded characters will not be written.
Example:
const buf = Buffer.allocUnsafe(256);
const len = buf.write('\u00bd + \u00bc = \u00be', 0);
// Prints: 12 bytes: ½ + ¼ = ¾
console.log(`${len} bytes: ${buf.toString('utf8', 0, len)}`);
buf.writeDoubleBE(value, offset[, noAssert])#
buf.writeDoubleLE(value, offset[, noAssert])#
value
<Number> Number to be written tobuf
offset
<Integer> Where to start writing. Must satisfy:0 <= offset <= buf.length - 8
noAssert
<Boolean> Skipvalue
andoffset
validation? Default:false
- Returns: <Integer>
offset
plus the number of bytes written
Writes value
to buf
at the specified offset
with specified endian
format (writeDoubleBE()
writes big endian, writeDoubleLE()
writes little
endian). value
should be a valid 64-bit double. Behavior is undefined when
value
is anything other than a 64-bit double.
Setting noAssert
to true
allows the encoded form of value
to extend beyond
the end of buf
, but the result should be considered undefined behavior.
Examples:
const buf = Buffer.allocUnsafe(8);
buf.writeDoubleBE(0xdeadbeefcafebabe, 0);
// Prints: <Buffer 43 eb d5 b7 dd f9 5f d7>
console.log(buf);
buf.writeDoubleLE(0xdeadbeefcafebabe, 0);
// Prints: <Buffer d7 5f f9 dd b7 d5 eb 43>
console.log(buf);
buf.writeFloatBE(value, offset[, noAssert])#
buf.writeFloatLE(value, offset[, noAssert])#
value
<Number> Number to be written tobuf
offset
<Integer> Where to start writing. Must satisfy:0 <= offset <= buf.length - 4
noAssert
<Boolean> Skipvalue
andoffset
validation? Default:false
- Returns: <Integer>
offset
plus the number of bytes written
Writes value
to buf
at the specified offset
with specified endian
format (writeFloatBE()
writes big endian, writeFloatLE()
writes little
endian). value
should be a valid 32-bit float. Behavior is undefined when
value
is anything other than a 32-bit float.
Setting noAssert
to true
allows the encoded form of value
to extend beyond
the end of buf
, but the result should be considered undefined behavior.
Examples:
const buf = Buffer.allocUnsafe(4);
buf.writeFloatBE(0xcafebabe, 0);
// Prints: <Buffer 4f 4a fe bb>
console.log(buf);
buf.writeFloatLE(0xcafebabe, 0);
// Prints: <Buffer bb fe 4a 4f>
console.log(buf);
buf.writeInt8(value, offset[, noAssert])#
value
<Integer> Number to be written tobuf
offset
<Integer> Where to start writing. Must satisfy:0 <= offset <= buf.length - 1
noAssert
<Boolean> Skipvalue
andoffset
validation? Default:false
- Returns: <Integer>
offset
plus the number of bytes written
Writes value
to buf
at the specified offset
. value
should be a valid
signed 8-bit integer. Behavior is undefined when value
is anything other than
a signed 8-bit integer.
Setting noAssert
to true
allows the encoded form of value
to extend beyond
the end of buf
, but the result should be considered undefined behavior.
value
is interpreted and written as a two's complement signed integer.
Examples:
const buf = Buffer.allocUnsafe(2);
buf.writeInt8(2, 0);
buf.writeInt8(-2, 1);
// Prints: <Buffer 02 fe>
console.log(buf);
buf.writeInt16BE(value, offset[, noAssert])#
buf.writeInt16LE(value, offset[, noAssert])#
value
<Integer> Number to be written tobuf
offset
<Integer> Where to start writing. Must satisfy:0 <= offset <= buf.length - 2
noAssert
<Boolean> Skipvalue
andoffset
validation? Default:false
- Returns: <Integer>
offset
plus the number of bytes written
Writes value
to buf
at the specified offset
with specified endian
format (writeInt16BE()
writes big endian, writeInt16LE()
writes little
endian). value
should be a valid signed 16-bit integer. Behavior is undefined
when value
is anything other than a signed 16-bit integer.
Setting noAssert
to true
allows the encoded form of value
to extend beyond
the end of buf
, but the result should be considered undefined behavior.
value
is interpreted and written as a two's complement signed integer.
Examples:
const buf = Buffer.allocUnsafe(4);
buf.writeInt16BE(0x0102, 0);
buf.writeInt16LE(0x0304, 2);
// Prints: <Buffer 01 02 04 03>
console.log(buf);
buf.writeInt32BE(value, offset[, noAssert])#
buf.writeInt32LE(value, offset[, noAssert])#
value
<Integer> Number to be written tobuf
offset
<Integer> Where to start writing. Must satisfy:0 <= offset <= buf.length - 4
noAssert
<Boolean> Skipvalue
andoffset
validation? Default:false
- Returns: <Integer>
offset
plus the number of bytes written
Writes value
to buf
at the specified offset
with specified endian
format (writeInt32BE()
writes big endian, writeInt32LE()
writes little
endian). value
should be a valid signed 32-bit integer. Behavior is undefined
when value
is anything other than a signed 32-bit integer.
Setting noAssert
to true
allows the encoded form of value
to extend beyond
the end of buf
, but the result should be considered undefined behavior.
value
is interpreted and written as a two's complement signed integer.
Examples:
const buf = Buffer.allocUnsafe(8);
buf.writeInt32BE(0x01020304, 0);
buf.writeInt32LE(0x05060708, 4);
// Prints: <Buffer 01 02 03 04 08 07 06 05>
console.log(buf);
buf.writeIntBE(value, offset, byteLength[, noAssert])#
buf.writeIntLE(value, offset, byteLength[, noAssert])#
value
<Integer> Number to be written tobuf
offset
<Integer> Where to start writing. Must satisfy:0 <= offset <= buf.length - byteLength
byteLength
<Integer> How many bytes to write. Must satisfy:0 < byteLength <= 6
noAssert
<Boolean> Skipvalue
,offset
, andbyteLength
validation? Default:false
- Returns: <Integer>
offset
plus the number of bytes written
Writes byteLength
bytes of value
to buf
at the specified offset
.
Supports up to 48 bits of accuracy. Behavior is undefined when value
is
anything other than a signed integer.
Setting noAssert
to true
allows the encoded form of value
to extend beyond
the end of buf
, but the result should be considered undefined behavior.
Examples:
const buf = Buffer.allocUnsafe(6);
buf.writeUIntBE(0x1234567890ab, 0, 6);
// Prints: <Buffer 12 34 56 78 90 ab>
console.log(buf);
buf.writeUIntLE(0x1234567890ab, 0, 6);
// Prints: <Buffer ab 90 78 56 34 12>
console.log(buf);
buf.writeUInt8(value, offset[, noAssert])#
value
<Integer> Number to be written tobuf
offset
<Integer> Where to start writing. Must satisfy:0 <= offset <= buf.length - 1
noAssert
<Boolean> Skipvalue
andoffset
validation? Default:false
- Returns: <Integer>
offset
plus the number of bytes written
Writes value
to buf
at the specified offset
. value
should be a
valid unsigned 8-bit integer. Behavior is undefined when value
is anything
other than an unsigned 8-bit integer.
Setting noAssert
to true
allows the encoded form of value
to extend beyond
the end of buf
, but the result should be considered undefined behavior.
Examples:
const buf = Buffer.allocUnsafe(4);
buf.writeUInt8(0x3, 0);
buf.writeUInt8(0x4, 1);
buf.writeUInt8(0x23, 2);
buf.writeUInt8(0x42, 3);
// Prints: <Buffer 03 04 23 42>
console.log(buf);
buf.writeUInt16BE(value, offset[, noAssert])#
buf.writeUInt16LE(value, offset[, noAssert])#
value
<Integer> Number to be written tobuf
offset
<Integer> Where to start writing. Must satisfy:0 <= offset <= buf.length - 2
noAssert
<Boolean> Skipvalue
andoffset
validation? Default:false
- Returns: <Integer>
offset
plus the number of bytes written
Writes value
to buf
at the specified offset
with specified endian
format (writeUInt16BE()
writes big endian, writeUInt16LE()
writes little
endian). value
should be a valid unsigned 16-bit integer. Behavior is
undefined when value
is anything other than an unsigned 16-bit integer.
Setting noAssert
to true
allows the encoded form of value
to extend beyond
the end of buf
, but the result should be considered undefined behavior.
Examples:
const buf = Buffer.allocUnsafe(4);
buf.writeUInt16BE(0xdead, 0);
buf.writeUInt16BE(0xbeef, 2);
// Prints: <Buffer de ad be ef>
console.log(buf);
buf.writeUInt16LE(0xdead, 0);
buf.writeUInt16LE(0xbeef, 2);
// Prints: <Buffer ad de ef be>
console.log(buf);
buf.writeUInt32BE(value, offset[, noAssert])#
buf.writeUInt32LE(value, offset[, noAssert])#
value
<Integer> Number to be written tobuf
offset
<Integer> Where to start writing. Must satisfy:0 <= offset <= buf.length - 4
noAssert
<Boolean> Skipvalue
andoffset
validation? Default:false
- Returns: <Integer>
offset
plus the number of bytes written
Writes value
to buf
at the specified offset
with specified endian
format (writeUInt32BE()
writes big endian, writeUInt32LE()
writes little
endian). value
should be a valid unsigned 32-bit integer. Behavior is
undefined when value
is anything other than an unsigned 32-bit integer.
Setting noAssert
to true
allows the encoded form of value
to extend beyond
the end of buf
, but the result should be considered undefined behavior.
Examples:
const buf = Buffer.allocUnsafe(4);
buf.writeUInt32BE(0xfeedface, 0);
// Prints: <Buffer fe ed fa ce>
console.log(buf);
buf.writeUInt32LE(0xfeedface, 0);
// Prints: <Buffer ce fa ed fe>
console.log(buf);
buf.writeUIntBE(value, offset, byteLength[, noAssert])#
buf.writeUIntLE(value, offset, byteLength[, noAssert])#
value
<Integer> Number to be written tobuf
offset
<Integer> Where to start writing. Must satisfy:0 <= offset <= buf.length - byteLength
byteLength
<Integer> How many bytes to write. Must satisfy:0 < byteLength <= 6
noAssert
<Boolean> Skipvalue
,offset
, andbyteLength
validation? Default:false
- Returns: <Integer>
offset
plus the number of bytes written
Writes byteLength
bytes of value
to buf
at the specified offset
.
Supports up to 48 bits of accuracy. Behavior is undefined when value
is
anything other than an unsigned integer.
Setting noAssert
to true
allows the encoded form of value
to extend beyond
the end of buf
, but the result should be considered undefined behavior.
Examples:
const buf = Buffer.allocUnsafe(6);
buf.writeUIntBE(0x1234567890ab, 0, 6);
// Prints: <Buffer 12 34 56 78 90 ab>
console.log(buf);
buf.writeUIntLE(0x1234567890ab, 0, 6);
// Prints: <Buffer ab 90 78 56 34 12>
console.log(buf);
buffer.INSPECT_MAX_BYTES#
- <Integer> Default:
50
Returns the maximum number of bytes that will be returned when
buf.inspect()
is called. This can be overridden by user modules. See
util.inspect()
for more details on buf.inspect()
behavior.
Note that this is a property on the buffer
module returned by
require('buffer')
, not on the Buffer
global or a Buffer
instance.
buffer.kMaxLength#
- <Integer> The largest size allowed for a single
Buffer
instance
On 32-bit architectures, this value is (2^30)-1
(~1GB).
On 64-bit architectures, this value is (2^31)-1
(~2GB).
Note that this is a property on the buffer
module returned by
require('buffer')
, not on the Buffer
global or a Buffer
instance.
buffer.transcode(source, fromEnc, toEnc)#
source
<Buffer> ABuffer
instancefromEnc
<String> The current encodingtoEnc
<String> To target encoding
Re-encodes the given Buffer
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.
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
.
Note that this is a property on the buffer
module returned by
require('buffer')
, not on the Buffer
global or a Buffer
instance.
Class: SlowBuffer#
Stability: 0 - Deprecated: Use Buffer.allocUnsafeSlow()
instead.
Returns an un-pooled Buffer
.
In order to avoid the garbage collection overhead of creating many individually
allocated Buffer
instances, by default allocations under 4KB are sliced from a
single larger allocated object. This approach improves both performance and memory
usage since v8 does not need to track and cleanup as many Persistent
objects.
In the case where a developer may need to retain a small chunk of memory from a
pool for an indeterminate amount of time, it may be appropriate to create an
un-pooled Buffer
instance using SlowBuffer
then copy out the relevant bits.
Example:
// Need to keep around a few small chunks of memory
const store = [];
socket.on('readable', () => {
const data = socket.read();
// Allocate for retained data
const sb = SlowBuffer(10);
// Copy the data into the new allocation
data.copy(sb, 0, 0, 10);
store.push(sb);
});
Use of SlowBuffer
should be used only as a last resort after a developer
has observed undue memory retention in their applications.
new SlowBuffer(size)#
Stability: 0 - Deprecated: Use Buffer.allocUnsafeSlow()
instead.
size
<Integer> The desired length of the newSlowBuffer
Allocates a new Buffer
of size
bytes. If the size
is larger than
buffer.kMaxLength
or smaller than 0, a RangeError
will be thrown.
A zero-length Buffer
will be created if size
is 0.
The underlying memory for SlowBuffer
instances is not initialized. The
contents of a newly created SlowBuffer
are unknown and could contain
sensitive data. Use buf.fill(0)
to initialize a SlowBuffer
to zeroes.
Example:
const SlowBuffer = require('buffer').SlowBuffer;
const buf = new SlowBuffer(5);
// Prints: (contents may vary): <Buffer 78 e0 82 02 01>
console.log(buf);
buf.fill(0);
// Prints: <Buffer 00 00 00 00 00>
console.log(buf);