Node.js v9.2.1 Documentation

Table of Contents

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 UTF-8 bytes [0x74, 0xc3, 0xa9, 0x73, 0x74].
const buf5 = Buffer.from('tést');

// Creates a Buffer containing Latin-1 bytes [0x74, 0xe9, 0x73, 0x74].
const buf6 = Buffer.from('tést', 'latin1');

Buffer.from(), Buffer.alloc(), and Buffer.allocUnsafe()#

In versions of Node.js prior to v6, Buffer instances were created using the Buffer constructor function, which allocates the returned Buffer differently based on what arguments are provided:

  • Passing a number as the first argument to Buffer() (e.g. new Buffer(10)), allocates a new Buffer object of the specified size. Prior to Node.js 8.0.0, the memory allocated for such Buffer instances is not initialized and can contain sensitive data. Such Buffer instances must be subsequently initialized by using either buf.fill(0) or by writing to the Buffer 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-uninitialized Buffer versus creating a slower-but-safer Buffer. Starting in Node.js 8.0.0, Buffer(num) and new Buffer(num) will return a Buffer with initialized memory.
  • Passing a string, array, or Buffer as the first argument copies the passed object's data into the Buffer.
  • Passing an ArrayBuffer returns a Buffer that shares allocated memory with the given ArrayBuffer.

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 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#

Added in: v5.10.0

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#

History
VersionChanges
v6.4.0

Introduced latin1 as an alias for binary.

v5.0.0

Removed the deprecated raw and raws 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 a Buffer 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 the Buffer 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 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 TypedArray#

History
VersionChanges
v3.0.0

The Buffers class now inherits from Uint8Array.

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:

  1. The Buffer object's memory is copied to the TypedArray, not shared.

  2. 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-element Uint32Array with elements [1, 2, 3, 4], not a Uint32Array 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:

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)#

History
VersionChanges
v7.2.1

Calling this constructor no longer emits a deprecation warning.

v7.0.0

Calling this constructor emits a deprecation warning now.

v6.0.0

Deprecated since: v6.0.0

Stability: 0 - Deprecated: Use Buffer.from(array) instead.

Allocates a new Buffer using an array of octets.

Example:

// Creates a new Buffer containing the UTF-8 bytes of the string 'buffer'
const buf = new Buffer([0x62, 0x75, 0x66, 0x66, 0x65, 0x72]);

new Buffer(arrayBuffer[, byteOffset [, length]])#

History
VersionChanges
v7.2.1

Calling this constructor no longer emits a deprecation warning.

v7.0.0

Calling this constructor emits a deprecation warning now.

v6.0.0

The byteOffset and length parameters are supported now.

v6.0.0

Deprecated since: v6.0.0

v3.0.0

Added in: v3.0.0

Stability: 0 - Deprecated: Use Buffer.from(arrayBuffer[, byteOffset [, length]]) instead.

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(buffer)#

History
VersionChanges
v7.2.1

Calling this constructor no longer emits a deprecation warning.

v7.0.0

Calling this constructor emits a deprecation warning now.

v6.0.0

Deprecated since: v6.0.0

Stability: 0 - Deprecated: Use Buffer.from(buffer) instead.
  • buffer <Buffer> An existing Buffer 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(size)#

History
VersionChanges
v8.0.0

new Buffer(size) will return zero-filled memory by default.

v7.2.1

Calling this constructor no longer emits a deprecation warning.

v7.0.0

Calling this constructor emits a deprecation warning now.

v6.0.0

Deprecated since: v6.0.0

Stability: 0 - Deprecated: Use Buffer.alloc() instead (also see Buffer.allocUnsafe()).
  • size <integer> The desired length of the new Buffer.

Allocates a new Buffer of size bytes. If the size is larger than buffer.constants.MAX_LENGTH or smaller than 0, a RangeError will be thrown. A zero-length Buffer will be created if size is 0.

Prior to Node.js 8.0.0, the underlying memory for Buffer instances created in this way is not initialized. The contents of a newly created Buffer are unknown and may contain sensitive data. Use Buffer.alloc(size) instead to initialize a Buffer to zeroes.

Example:

const buf = new Buffer(10);

// Prints: <Buffer 00 00 00 00 00 00 00 00 00 00>
console.log(buf);

new Buffer(string[, encoding])#

History
VersionChanges
v7.2.1

Calling this constructor no longer emits a deprecation warning.

v7.0.0

Calling this constructor emits a deprecation warning now.

v6.0.0

Deprecated since: v6.0.0

Stability: 0 - Deprecated: Use Buffer.from(string[, encoding]) instead.
  • string <string> String to encode.
  • encoding <string> The encoding of string. Default: 'utf8'

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]])#

History
VersionChanges
v9.2.1

Specifying an invalid string for fill now results in a zero-filled buffer.

v5.10.0

Added in: v5.10.0

  • size <integer> The desired length of the new Buffer.
  • fill <string> | <Buffer> | <integer> A value to pre-fill the new Buffer with. Default: 0
  • encoding <string> If fill 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.constants.MAX_LENGTH 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)#

History
VersionChanges
v7.0.0

Passing a negative size will now throw an error.

v5.10.0

Added in: v5.10.0

  • size <integer> The desired length of the new Buffer.

Allocates a new Buffer of size bytes. If the size is larger than buffer.constants.MAX_LENGTH 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)#

Added in: v5.12.0
  • size <integer> The desired length of the new Buffer.

Allocates a new Buffer of size bytes. If the size is larger than buffer.constants.MAX_LENGTH 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])#

History
VersionChanges
v7.0.0

Passing invalid input will now throw an error.

v5.10.0

The string parameter can now be any TypedArray, DataView or ArrayBuffer.

v0.1.90

Added in: v0.1.90

Returns the actual byte length of a string. This is not the same as String.prototype.length since that returns the number of characters in a string.

Note: For 'base64' and 'hex', this function assumes valid input. For strings that contain non-Base64/Hex-encoded data (e.g. whitespace), the return value might be greater than the length of a Buffer created from the string.

Example:

const str = '\u00bd + \u00bc = \u00be';

// Prints: ½ + ¼ = ¾: 9 characters, 12 bytes
console.log(`${str}: ${str.length} characters, ` +
            `${Buffer.byteLength(str, 'utf8')} bytes`);

When string is a Buffer/DataView/TypedArray/ArrayBuffer, the actual byte length is returned.

Class Method: Buffer.compare(buf1, buf2)#

History
VersionChanges
v8.0.0

The arguments can now be Uint8Arrays.

v0.11.13

Added in: v0.11.13

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])#

History
VersionChanges
v8.0.0

The elements of list can now be Uint8Arrays.

v0.7.11

Added in: v0.7.11

Returns a new Buffer which is the result of concatenating all the Buffer instances in the list together.

If the list has no items, or if the totalLength is 0, then a new zero-length Buffer is returned.

If totalLength is not provided, it is calculated from the Buffer instances in list. This however causes an additional loop to be executed in order to calculate the totalLength, so it is faster to provide the length explicitly if it is already known.

If totalLength is provided, it is coerced to an unsigned integer. If the combined length of the Buffers in list exceeds totalLength, the result is truncated to totalLength.

Example: Create a single Buffer from a list of three Buffer instances

const buf1 = Buffer.alloc(10);
const buf2 = Buffer.alloc(14);
const buf3 = Buffer.alloc(18);
const totalLength = buf1.length + buf2.length + buf3.length;

// Prints: 42
console.log(totalLength);

const bufA = Buffer.concat([buf1, buf2, buf3], totalLength);

// Prints: <Buffer 00 00 00 00 ...>
console.log(bufA);

// Prints: 42
console.log(bufA.length);

Class Method: Buffer.from(array)#

Added in: v5.10.0

Allocates a new Buffer using an array of octets.

Example:

// Creates a new Buffer containing UTF-8 bytes of the string 'buffer'
const buf = Buffer.from([0x62, 0x75, 0x66, 0x66, 0x65, 0x72]);

A TypeError will be thrown if array is not an Array.

Class Method: Buffer.from(arrayBuffer[, byteOffset[, length]])#

Added in: v5.10.0

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)#

Added in: v5.10.0
  • buffer <Buffer> An existing Buffer 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])#

Added in: v5.10.0
  • string <string> A string to encode.
  • encoding <string> The encoding of string. Default: 'utf8'

Creates a new Buffer containing the given JavaScript string string. If provided, the encoding parameter identifies the character encoding of string.

Examples:

const buf1 = Buffer.from('this is a tést');

// Prints: this is a tést
console.log(buf1.toString());

// Prints: this is a tC)st
console.log(buf1.toString('ascii'));


const buf2 = Buffer.from('7468697320697320612074c3a97374', 'hex');

// Prints: this is a tést
console.log(buf2.toString());

A TypeError will be thrown if string is not a string.

Class Method: Buffer.from(object[, offsetOrEncoding[, length]])#

Added in: v8.2.0
  • object <Object> An object supporting Symbol.toPrimitive or valueOf()
  • offsetOrEncoding <number> | <string> A byte-offset or encoding, depending on the value returned either by object.valueOf() or object[Symbol.toPrimitive]().
  • length <number> A length, depending on the value returned either by object.valueOf() or object[Symbol.toPrimitive]().

For objects whose valueOf() function returns a value not strictly equal to object, returns Buffer.from(object.valueOf(), offsetOrEncoding, length).

For example:

const buf = Buffer.from(new String('this is a test'));
// <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](), offsetOrEncoding, length).

For example:

class Foo {
  [Symbol.toPrimitive]() {
    return 'this is a test';
  }
}

const buf = Buffer.from(new Foo(), 'utf8');
// <Buffer 74 68 69 73 20 69 73 20 61 20 74 65 73 74>

Class Method: Buffer.isBuffer(obj)#

Added in: v0.1.101

Returns true if obj is a Buffer, false otherwise.

Class Method: Buffer.isEncoding(encoding)#

Added in: v0.9.1

Returns true if encoding contains a supported character encoding, or false otherwise.

Class Property: Buffer.poolSize#

Added in: v0.11.3

This is the number of bytes used to determine the size of pre-allocated, internal Buffer instances used for pooling. This value may be modified.

buf[index]#

The index operator [index] can be used to get and set the octet at position index in buf. The values refer to individual bytes, so the legal value range is between 0x00 and 0xFF (hex) or 0 and 255 (decimal).

This operator is inherited from Uint8Array, so its behavior on out-of-bounds access is the same as UInt8Array - that is, getting returns undefined and setting does nothing.

Example: Copy an ASCII string into a Buffer, one byte at a time

const str = 'Node.js';
const buf = Buffer.allocUnsafe(str.length);

for (let i = 0; i < str.length; i++) {
  buf[i] = str.charCodeAt(i);
}

// Prints: Node.js
console.log(buf.toString('ascii'));

buf.buffer#

The buffer property references the underlying ArrayBuffer object based on which this Buffer object is created.

const arrayBuffer = new ArrayBuffer(16);
const buffer = Buffer.from(arrayBuffer);

console.log(buffer.buffer === arrayBuffer);
// Prints: true

buf.compare(target[, targetStart[, targetEnd[, sourceStart[, sourceEnd]]]])#

History
VersionChanges
v8.0.0

The target parameter can now be a Uint8Array.

v5.11.0

Additional parameters for specifying offsets are supported now.

v0.11.13

Added in: v0.11.13

  • target <Buffer> | <Uint8Array> A Buffer or Uint8Array to compare to.
  • targetStart <integer> The offset within target at which to begin comparison. Default: 0
  • targetEnd <integer> The offset with target at which to end comparison (not inclusive). Ignored when targetStart is undefined. Default: target.length
  • sourceStart <integer> The offset within buf at which to begin comparison. Ignored when targetStart is undefined. Default: 0
  • sourceEnd <integer> The offset within buf at which to end comparison (not inclusive). Ignored when targetStart is undefined. 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 if target is the same as buf
  • 1 is returned if target should come before buf when sorted.
  • -1 is returned if target should come after buf 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]]])#

Added in: v0.1.90
  • target <Buffer> | <Uint8Array> A Buffer or Uint8Array to copy into.
  • targetStart <integer> The offset within target at which to begin copying to. Default: 0
  • sourceStart <integer> The offset within buf at which to begin copying from. Ignored when targetStart is undefined. Default: 0
  • sourceEnd <integer> The offset within buf at which to stop copying (not inclusive). Ignored when sourceStart is undefined. 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()#

Added in: v1.1.0

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)#

History
VersionChanges
v8.0.0

The arguments can now be Uint8Arrays.

v0.11.13

Added in: v0.11.13

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])#

History
VersionChanges
v5.7.0

The encoding parameter is supported now.

v0.5.0

Added in: v0.5.0

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'));

If value contains invalid characters, it is truncated; if no valid fill data remains, no filling is performed:

const buf = Buffer.allocUnsafe(5);
// Prints: <Buffer 61 61 61 61 61>
console.log(buf.fill('a'));
// Prints: <Buffer aa aa aa aa aa>
console.log(buf.fill('aazz', 'hex'));
// Prints: <Buffer aa aa aa aa aa>
console.log(buf.fill('zz', 'hex'));

buf.includes(value[, byteOffset][, encoding])#

Added in: v5.3.0
  • value <string> | <Buffer> | <integer> What to search for.
  • byteOffset <integer> Where to begin searching in buf. Default: 0
  • encoding <string> If value is a string, this is its encoding. Default: 'utf8'
  • Returns: <boolean> true if value was found in buf, false otherwise.

Equivalent to buf.indexOf() !== -1.

Examples:

const buf = Buffer.from('this is a buffer');

// Prints: true
console.log(buf.includes('this'));

// Prints: true
console.log(buf.includes('is'));

// Prints: true
console.log(buf.includes(Buffer.from('a buffer')));

// Prints: true
// (97 is the decimal ASCII value for 'a')
console.log(buf.includes(97));

// Prints: false
console.log(buf.includes(Buffer.from('a buffer example')));

// Prints: true
console.log(buf.includes(Buffer.from('a buffer example').slice(0, 8)));

// Prints: false
console.log(buf.includes('this', 4));

buf.indexOf(value[, byteOffset][, encoding])#

History
VersionChanges
v8.0.0

The value can now be a Uint8Array.

v5.7.0, v4.4.0

When encoding is being passed, the byteOffset parameter is no longer required.

v1.5.0

Added in: v1.5.0

  • value <string> | <Buffer> | <Uint8Array> | <integer> What to search for.
  • byteOffset <integer> Where to begin searching in buf. Default: 0
  • encoding <string> If value is a string, this is its encoding. Default: 'utf8'
  • Returns: <integer> The index of the first occurrence of value in buf or -1 if buf does not contain value.

If value is:

  • a string, value is interpreted according to the character encoding in encoding.
  • a Buffer or Uint8Array, value will be used in its entirety. To compare a partial Buffer, use buf.slice().
  • a number, value will be interpreted as an unsigned 8-bit integer value between 0 and 255.

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', []));

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()#

Added in: v1.1.0

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])#

History
VersionChanges
v8.0.0

The value can now be a Uint8Array.

v6.0.0

Added in: v6.0.0

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', []));

If value is an empty string or empty Buffer, byteOffset will be returned.

buf.length#

Added in: v0.1.90

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.parent#

Deprecated since: v8.0.0
Stability: 0 - Deprecated: Use buf.buffer instead.

The buf.parent property is a deprecated alias for buf.buffer.

buf.readDoubleBE(offset[, noAssert])#

buf.readDoubleLE(offset[, noAssert])#

Added in: v0.11.15
  • offset <integer> Number of bytes to skip before starting to read. Must satisfy: 0 <= offset <= buf.length - 8.
  • noAssert <boolean> Skip offset 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])#

Added in: v0.11.15
  • offset <integer> Number of bytes to skip before starting to read. Must satisfy: 0 <= offset <= buf.length - 4.
  • noAssert <boolean> Skip offset 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])#

Added in: v0.5.0
  • offset <integer> Number of bytes to skip before starting to read. Must satisfy: 0 <= offset <= buf.length - 1.
  • noAssert <boolean> Skip offset 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])#

Added in: v0.5.5
  • offset <integer> Number of bytes to skip before starting to read. Must satisfy: 0 <= offset <= buf.length - 2.
  • noAssert <boolean> Skip offset 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])#

Added in: v0.5.5
  • offset <integer> Number of bytes to skip before starting to read. Must satisfy: 0 <= offset <= buf.length - 4.
  • noAssert <boolean> Skip offset 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])#

Added in: v0.11.15
  • offset <integer> Number of bytes to skip before starting to read. Must satisfy: 0 <= offset <= buf.length - byteLength.
  • byteLength <integer> Number of bytes to read. Must satisfy: 0 < byteLength <= 6.
  • noAssert <boolean> Skip offset and byteLength 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])#

Added in: v0.5.0
  • offset <integer> Number of bytes to skip before starting to read. Must satisfy: 0 <= offset <= buf.length - 1.
  • noAssert <boolean> Skip offset 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])#

Added in: v0.5.5
  • offset <integer> Number of bytes to skip before starting to read. Must satisfy: 0 <= offset <= buf.length - 2.
  • noAssert <boolean> Skip offset 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])#

Added in: v0.5.5
  • offset <integer> Number of bytes to skip before starting to read. Must satisfy: 0 <= offset <= buf.length - 4.
  • noAssert <boolean> Skip offset 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])#

Added in: v0.11.15
  • offset <integer> Number of bytes to skip before starting to read. Must satisfy: 0 <= offset <= buf.length - byteLength.
  • byteLength <integer> Number of bytes to read. Must satisfy: 0 < byteLength <= 6.
  • noAssert <boolean> Skip offset and byteLength 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]])#

History
VersionChanges
v7.1.0, v6.9.2

Coercing the offsets to integers now handles values outside the 32-bit integer range properly.

v7.0.0

All offsets are now coerced to integers before doing any calculations with them.

v0.3.0

Added in: v0.3.0

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.

Note: 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()#

Added in: v5.10.0

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()#

Added in: v5.10.0

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()#

Added in: v6.3.0

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.toJSON()#

Added in: v0.9.2

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.toString([encoding[, start[, end]]])#

Added in: v0.1.90
  • 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.

The maximum length of a string instance (in UTF-16 code units) is available as buffer.constants.MAX_STRING_LENGTH.

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.values()#

Added in: v1.1.0

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])#

Added in: v0.1.90
  • string <string> String to be written to buf.
  • offset <integer> Number of bytes to skip before starting to write string. Default: 0
  • length <integer> Number of bytes to write. Default: buf.length - offset
  • encoding <string> The character encoding of string. 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])#

Added in: v0.11.15
  • value <number> Number to be written to buf.
  • offset <integer> Number of bytes to skip before starting to write. Must satisfy: 0 <= offset <= buf.length - 8.
  • noAssert <boolean> Skip value and offset 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])#

Added in: v0.11.15
  • value <number> Number to be written to buf.
  • offset <integer> Number of bytes to skip before starting to write. Must satisfy: 0 <= offset <= buf.length - 4.
  • noAssert <boolean> Skip value and offset 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])#

Added in: v0.5.0
  • value <integer> Number to be written to buf.
  • offset <integer> Number of bytes to skip before starting to write. Must satisfy: 0 <= offset <= buf.length - 1.
  • noAssert <boolean> Skip value and offset 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])#

Added in: v0.5.5
  • value <integer> Number to be written to buf.
  • offset <integer> Number of bytes to skip before starting to write. Must satisfy: 0 <= offset <= buf.length - 2.
  • noAssert <boolean> Skip value and offset 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])#

Added in: v0.5.5
  • value <integer> Number to be written to buf.
  • offset <integer> Number of bytes to skip before starting to write. Must satisfy: 0 <= offset <= buf.length - 4.
  • noAssert <boolean> Skip value and offset 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])#

Added in: v0.11.15
  • value <integer> Number to be written to buf.
  • offset <integer> Number of bytes to skip before starting to write. Must satisfy: 0 <= offset <= buf.length - byteLength.
  • byteLength <integer> Number of bytes to write. Must satisfy: 0 < byteLength <= 6.
  • noAssert <boolean> Skip value, offset, and byteLength 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.writeIntBE(0x1234567890ab, 0, 6);

// Prints: <Buffer 12 34 56 78 90 ab>
console.log(buf);

buf.writeIntLE(0x1234567890ab, 0, 6);

// Prints: <Buffer ab 90 78 56 34 12>
console.log(buf);

buf.writeUInt8(value, offset[, noAssert])#

Added in: v0.5.0
  • value <integer> Number to be written to buf.
  • offset <integer> Number of bytes to skip before starting to write. Must satisfy: 0 <= offset <= buf.length - 1.
  • noAssert <boolean> Skip value and offset 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])#

Added in: v0.5.5
  • value <integer> Number to be written to buf.
  • offset <integer> Number of bytes to skip before starting to write. Must satisfy: 0 <= offset <= buf.length - 2.
  • noAssert <boolean> Skip value and offset 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])#

Added in: v0.5.5
  • value <integer> Number to be written to buf.
  • offset <integer> Number of bytes to skip before starting to write. Must satisfy: 0 <= offset <= buf.length - 4.
  • noAssert <boolean> Skip value and offset 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])#

Added in: v0.5.5
  • value <integer> Number to be written to buf.
  • offset <integer> Number of bytes to skip before starting to write. Must satisfy: 0 <= offset <= buf.length - byteLength.
  • byteLength <integer> Number of bytes to write. Must satisfy: 0 < byteLength <= 6.
  • noAssert <boolean> Skip value, offset, and byteLength 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#

Added in: v0.5.4

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#

Added in: v3.0.0
  • <integer> The largest size allowed for a single Buffer instance.

An alias for buffer.constants.MAX_LENGTH

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)#

History
VersionChanges
v8.0.0

The source parameter can now be a Uint8Array.

v7.1.0

Added in: v7.1.0

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.

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#

Deprecated since: v6.0.0
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)#

Deprecated since: v6.0.0
Stability: 0 - Deprecated: Use Buffer.allocUnsafeSlow() instead.
  • size <integer> The desired length of the new SlowBuffer.

Allocates a new Buffer of size bytes. If the size is larger than buffer.constants.MAX_LENGTH 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 may contain sensitive data. Use buf.fill(0) to initialize a SlowBuffer to zeroes.

Example:

const { SlowBuffer } = require('buffer');

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);

Buffer Constants#

Added in: 8.2.0

Note that buffer.constants is a property on the buffer module returned by require('buffer'), not on the Buffer global or a Buffer instance.

buffer.constants.MAX_LENGTH#

Added in: 8.2.0
  • <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).

This value is also available as buffer.kMaxLength.

buffer.constants.MAX_STRING_LENGTH#

Added in: 8.2.0
  • <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.