Module

std/node/buffer.ts

Deno standard library
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class Buffer
extends Uint8Array
import { Buffer } from "https://deno.land/std@0.145.0/node/buffer.ts";

Buffer objects are used to represent a fixed-length sequence of bytes. Many Node.js APIs support Buffers.

The Buffer class is a subclass of JavaScript's Uint8Array class and extends it with methods that cover additional use cases. Node.js APIs accept plain Uint8Array s wherever Buffers are supported as well.

While the Buffer class is available within the global scope, it is still recommended to explicitly reference it via an import or require statement.

import { Buffer } from 'buffer';

// Creates a zero-filled Buffer of length 10.
const buf1 = Buffer.alloc(10);

// Creates a Buffer of length 10,
// filled with bytes which all have the value `1`.
const buf2 = Buffer.alloc(10, 1);

// Creates an uninitialized buffer of length 10.
// This is faster than calling Buffer.alloc() but the returned
// Buffer instance might contain old data that needs to be
// overwritten using fill(), write(), or other functions that fill the Buffer's
// contents.
const buf3 = Buffer.allocUnsafe(10);

// Creates a Buffer containing the bytes [1, 2, 3].
const buf4 = Buffer.from([1, 2, 3]);

// Creates a Buffer containing the bytes [1, 1, 1, 1] – the entries
// are all truncated using `(value & 255)` to fit into the range 0–255.
const buf5 = Buffer.from([257, 257.5, -255, '1']);

// Creates a Buffer containing the UTF-8-encoded bytes for the string 'tést':
// [0x74, 0xc3, 0xa9, 0x73, 0x74] (in hexadecimal notation)
// [116, 195, 169, 115, 116] (in decimal notation)
const buf6 = Buffer.from('tést');

// Creates a Buffer containing the Latin-1 bytes [0x74, 0xe9, 0x73, 0x74].
const buf7 = Buffer.from('tést', 'latin1');

Constructors

new
Buffer(str: string, encoding?: Encoding)

Allocates a new buffer containing the given {str}.

new
Buffer(size: number)

Allocates a new buffer of {size} octets.

new
Buffer(array: Uint8Array)

Allocates a new buffer containing the given {array} of octets.

new
Buffer(arrayBuffer: ArrayBuffer | SharedArrayBuffer)

Produces a Buffer backed by the same allocated memory as the given {ArrayBuffer}/{SharedArrayBuffer}.

new
Buffer(array: ReadonlyArray<unknown>)

Allocates a new buffer containing the given {array} of octets.

new
Buffer(buffer: Buffer)

Copies the passed {buffer} data onto a new {Buffer} instance.

Methods

compare(
target: Uint8Array,
targetStart?: number,
targetEnd?: number,
sourceStart?: number,
sourceEnd?: number,
): number

Compares buf with target and returns a number indicating whether bufcomes 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.
import { Buffer } from 'buffer';

const buf1 = Buffer.from('ABC');
const buf2 = Buffer.from('BCD');
const buf3 = Buffer.from('ABCD');

console.log(buf1.compare(buf1));
// Prints: 0
console.log(buf1.compare(buf2));
// Prints: -1
console.log(buf1.compare(buf3));
// Prints: -1
console.log(buf2.compare(buf1));
// Prints: 1
console.log(buf2.compare(buf3));
// Prints: 1
console.log([buf1, buf2, buf3].sort(Buffer.compare));
// Prints: [ <Buffer 41 42 43>, <Buffer 41 42 43 44>, <Buffer 42 43 44> ]
// (This result is equal to: [buf1, buf3, buf2].)

The optional targetStart, targetEnd, sourceStart, and sourceEndarguments can be used to limit the comparison to specific ranges within targetand buf respectively.

import { Buffer } from 'buffer';

const buf1 = Buffer.from([1, 2, 3, 4, 5, 6, 7, 8, 9]);
const buf2 = Buffer.from([5, 6, 7, 8, 9, 1, 2, 3, 4]);

console.log(buf1.compare(buf2, 5, 9, 0, 4));
// Prints: 0
console.log(buf1.compare(buf2, 0, 6, 4));
// Prints: -1
console.log(buf1.compare(buf2, 5, 6, 5));
// Prints: 1

ERR_OUT_OF_RANGE is thrown if targetStart < 0, sourceStart < 0,targetEnd > target.byteLength, or sourceEnd > source.byteLength.

copy(
target: Uint8Array,
targetStart?: number,
sourceStart?: number,
sourceEnd?: number,
): number

Copies data from a region of buf to a region in target, even if the targetmemory region overlaps with buf.

TypedArray.prototype.set() performs the same operation, and is available for all TypedArrays, including Node.js Buffers, although it takes different function arguments.

import { Buffer } from 'buffer';

// Create two `Buffer` instances.
const buf1 = Buffer.allocUnsafe(26);
const buf2 = Buffer.allocUnsafe(26).fill('!');

for (let i = 0; i < 26; i++) {
  // 97 is the decimal ASCII value for 'a'.
  buf1[i] = i + 97;
}

// Copy `buf1` bytes 16 through 19 into `buf2` starting at byte 8 of `buf2`.
buf1.copy(buf2, 8, 16, 20);
// This is equivalent to:
// buf2.set(buf1.subarray(16, 20), 8);

console.log(buf2.toString('ascii', 0, 25));
// Prints: !!!!!!!!qrst!!!!!!!!!!!!!
import { Buffer } from 'buffer';

// Create a `Buffer` and copy data from one region to an overlapping region
// within the same `Buffer`.

const buf = Buffer.allocUnsafe(26);

for (let i = 0; i < 26; i++) {
  // 97 is the decimal ASCII value for 'a'.
  buf[i] = i + 97;
}

buf.copy(buf, 0, 4, 10);

console.log(buf.toString());
// Prints: efghijghijklmnopqrstuvwxyz
entries(): IterableIterator<[number, number]>

Creates and returns an iterator of [index, byte] pairs from the contents of buf.

import { Buffer } from 'buffer';

// Log the entire contents of a `Buffer`.

const buf = Buffer.from('buffer');

for (const pair of buf.entries()) {
  console.log(pair);
}
// Prints:
//   [0, 98]
//   [1, 117]
//   [2, 102]
//   [3, 102]
//   [4, 101]
//   [5, 114]
equals(otherBuffer: Uint8Array): boolean

Returns true if both buf and otherBuffer have exactly the same bytes,false otherwise. Equivalent to buf.compare(otherBuffer) === 0.

import { Buffer } from 'buffer';

const buf1 = Buffer.from('ABC');
const buf2 = Buffer.from('414243', 'hex');
const buf3 = Buffer.from('ABCD');

console.log(buf1.equals(buf2));
// Prints: true
console.log(buf1.equals(buf3));
// Prints: false
fill(
value: string | Uint8Array | number,
offset?: number,
end?: number,
encoding?: Encoding,
): this

Fills buf with the specified value. If the offset and end are not given, the entire buf will be filled:

import { Buffer } from 'buffer';

// Fill a `Buffer` with the ASCII character 'h'.

const b = Buffer.allocUnsafe(50).fill('h');

console.log(b.toString());
// Prints: hhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh

value is coerced to a uint32 value if it is not a string, Buffer, or integer. If the resulting integer is greater than 255 (decimal), buf will be filled with value &#x26; 255.

If the final write of a fill() operation falls on a multi-byte character, then only the bytes of that character that fit into buf are written:

import { Buffer } from 'buffer';

// Fill a `Buffer` with character that takes up two bytes in UTF-8.

console.log(Buffer.allocUnsafe(5).fill('\u0222'));
// Prints: <Buffer c8 a2 c8 a2 c8>

If value contains invalid characters, it is truncated; if no valid fill data remains, an exception is thrown:

import { Buffer } from 'buffer';

const buf = Buffer.allocUnsafe(5);

console.log(buf.fill('a'));
// Prints: <Buffer 61 61 61 61 61>
console.log(buf.fill('aazz', 'hex'));
// Prints: <Buffer aa aa aa aa aa>
console.log(buf.fill('zz', 'hex'));
// Throws an exception.
includes(
value: string | number | Buffer,
byteOffset?: number,
encoding?: Encoding,
): boolean

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

import { Buffer } from 'buffer';

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

console.log(buf.includes('this'));
// Prints: true
console.log(buf.includes('is'));
// Prints: true
console.log(buf.includes(Buffer.from('a buffer')));
// Prints: true
console.log(buf.includes(97));
// Prints: true (97 is the decimal ASCII value for 'a')
console.log(buf.includes(Buffer.from('a buffer example')));
// Prints: false
console.log(buf.includes(Buffer.from('a buffer example').slice(0, 8)));
// Prints: true
console.log(buf.includes('this', 4));
// Prints: false
indexOf(
value: string | number | Uint8Array,
byteOffset?: number,
encoding?: Encoding,
): number

If value is:

  • a string, value is interpreted according to the character encoding inencoding.
  • 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.
import { Buffer } from 'buffer';

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

console.log(buf.indexOf('this'));
// Prints: 0
console.log(buf.indexOf('is'));
// Prints: 2
console.log(buf.indexOf(Buffer.from('a buffer')));
// Prints: 8
console.log(buf.indexOf(97));
// Prints: 8 (97 is the decimal ASCII value for 'a')
console.log(buf.indexOf(Buffer.from('a buffer example')));
// Prints: -1
console.log(buf.indexOf(Buffer.from('a buffer example').slice(0, 8)));
// Prints: 8

const utf16Buffer = Buffer.from('\u039a\u0391\u03a3\u03a3\u0395', 'utf16le');

console.log(utf16Buffer.indexOf('\u03a3', 0, 'utf16le'));
// Prints: 4
console.log(utf16Buffer.indexOf('\u03a3', -4, 'utf16le'));
// Prints: 6

If value is not a string, number, or Buffer, this method will throw aTypeError. If value is a number, it will be coerced to a valid byte value, an integer between 0 and 255.

If byteOffset is not a number, it will be coerced to a number. If the result of coercion is NaN or 0, then the entire buffer will be searched. This behavior matches String.prototype.indexOf().

import { Buffer } from 'buffer';

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 andbyteOffset is at least buf.length, buf.length will be returned.

keys(): IterableIterator<number>

Creates and returns an iterator of buf keys (indices).

import { Buffer } from 'buffer';

const buf = Buffer.from('buffer');

for (const key of buf.keys()) {
  console.log(key);
}
// Prints:
//   0
//   1
//   2
//   3
//   4
//   5
lastIndexOf(
value: string | number | Uint8Array,
byteOffset?: number,
encoding?: Encoding,
): number

Identical to buf.indexOf(), except the last occurrence of value is found rather than the first occurrence.

import { Buffer } from 'buffer';

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

console.log(buf.lastIndexOf('this'));
// Prints: 0
console.log(buf.lastIndexOf('buffer'));
// Prints: 17
console.log(buf.lastIndexOf(Buffer.from('buffer')));
// Prints: 17
console.log(buf.lastIndexOf(97));
// Prints: 15 (97 is the decimal ASCII value for 'a')
console.log(buf.lastIndexOf(Buffer.from('yolo')));
// Prints: -1
console.log(buf.lastIndexOf('buffer', 5));
// Prints: 5
console.log(buf.lastIndexOf('buffer', 4));
// Prints: -1

const utf16Buffer = Buffer.from('\u039a\u0391\u03a3\u03a3\u0395', 'utf16le');

console.log(utf16Buffer.lastIndexOf('\u03a3', undefined, 'utf16le'));
// Prints: 6
console.log(utf16Buffer.lastIndexOf('\u03a3', -5, 'utf16le'));
// Prints: 4

If value is not a string, number, or Buffer, this method will throw aTypeError. 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.prototype.lastIndexOf().

import { Buffer } from 'buffer';

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.

readBigInt64BE(offset?: number): bigint

Reads a signed, big-endian 64-bit integer from buf at the specified offset.

Integers read from a Buffer are interpreted as two's complement signed values.

readBigInt64LE(offset?: number): bigint

Reads a signed, little-endian 64-bit integer from buf at the specifiedoffset.

Integers read from a Buffer are interpreted as two's complement signed values.

readBigUInt64BE(offset?: number): bigint

Reads an unsigned, big-endian 64-bit integer from buf at the specifiedoffset.

This function is also available under the readBigUint64BE alias.

import { Buffer } from 'buffer';

const buf = Buffer.from([0x00, 0x00, 0x00, 0x00, 0xff, 0xff, 0xff, 0xff]);

console.log(buf.readBigUInt64BE(0));
// Prints: 4294967295n
readBigUInt64LE(offset?: number): bigint

Reads an unsigned, little-endian 64-bit integer from buf at the specifiedoffset.

This function is also available under the readBigUint64LE alias.

import { Buffer } from 'buffer';

const buf = Buffer.from([0x00, 0x00, 0x00, 0x00, 0xff, 0xff, 0xff, 0xff]);

console.log(buf.readBigUInt64LE(0));
// Prints: 18446744069414584320n
readDoubleBE(offset?: number): number

Reads a 64-bit, big-endian double from buf at the specified offset.

import { Buffer } from 'buffer';

const buf = Buffer.from([1, 2, 3, 4, 5, 6, 7, 8]);

console.log(buf.readDoubleBE(0));
// Prints: 8.20788039913184e-304
readDoubleLE(offset?: number): number

Reads a 64-bit, little-endian double from buf at the specified offset.

import { Buffer } from 'buffer';

const buf = Buffer.from([1, 2, 3, 4, 5, 6, 7, 8]);

console.log(buf.readDoubleLE(0));
// Prints: 5.447603722011605e-270
console.log(buf.readDoubleLE(1));
// Throws ERR_OUT_OF_RANGE.
readFloatBE(offset?: number): number

Reads a 32-bit, big-endian float from buf at the specified offset.

import { Buffer } from 'buffer';

const buf = Buffer.from([1, 2, 3, 4]);

console.log(buf.readFloatBE(0));
// Prints: 2.387939260590663e-38
readFloatLE(offset?: number): number

Reads a 32-bit, little-endian float from buf at the specified offset.

import { Buffer } from 'buffer';

const buf = Buffer.from([1, 2, 3, 4]);

console.log(buf.readFloatLE(0));
// Prints: 1.539989614439558e-36
console.log(buf.readFloatLE(1));
// Throws ERR_OUT_OF_RANGE.
readInt16BE(offset?: number): number

Reads a signed, big-endian 16-bit integer from buf at the specified offset.

Integers read from a Buffer are interpreted as two's complement signed values.

import { Buffer } from 'buffer';

const buf = Buffer.from([0, 5]);

console.log(buf.readInt16BE(0));
// Prints: 5
readInt16LE(offset?: number): number

Reads a signed, little-endian 16-bit integer from buf at the specifiedoffset.

Integers read from a Buffer are interpreted as two's complement signed values.

import { Buffer } from 'buffer';

const buf = Buffer.from([0, 5]);

console.log(buf.readInt16LE(0));
// Prints: 1280
console.log(buf.readInt16LE(1));
// Throws ERR_OUT_OF_RANGE.
readInt32BE(offset?: number): number

Reads a signed, big-endian 32-bit integer from buf at the specified offset.

Integers read from a Buffer are interpreted as two's complement signed values.

import { Buffer } from 'buffer';

const buf = Buffer.from([0, 0, 0, 5]);

console.log(buf.readInt32BE(0));
// Prints: 5
readInt32LE(offset?: number): number

Reads a signed, little-endian 32-bit integer from buf at the specifiedoffset.

Integers read from a Buffer are interpreted as two's complement signed values.

import { Buffer } from 'buffer';

const buf = Buffer.from([0, 0, 0, 5]);

console.log(buf.readInt32LE(0));
// Prints: 83886080
console.log(buf.readInt32LE(1));
// Throws ERR_OUT_OF_RANGE.
readInt8(offset?: number): number

Reads a signed 8-bit integer from buf at the specified offset.

Integers read from a Buffer are interpreted as two's complement signed values.

import { Buffer } from 'buffer';

const buf = Buffer.from([-1, 5]);

console.log(buf.readInt8(0));
// Prints: -1
console.log(buf.readInt8(1));
// Prints: 5
console.log(buf.readInt8(2));
// Throws ERR_OUT_OF_RANGE.
readIntBE(offset: number, byteLength: number): number

Reads byteLength number of bytes from buf at the specified offsetand interprets the result as a big-endian, two's complement signed value supporting up to 48 bits of accuracy.

import { Buffer } from 'buffer';

const buf = Buffer.from([0x12, 0x34, 0x56, 0x78, 0x90, 0xab]);

console.log(buf.readIntBE(0, 6).toString(16));
// Prints: 1234567890ab
console.log(buf.readIntBE(1, 6).toString(16));
// Throws ERR_OUT_OF_RANGE.
console.log(buf.readIntBE(1, 0).toString(16));
// Throws ERR_OUT_OF_RANGE.
readIntLE(offset: number, byteLength: number): number

Reads byteLength number of bytes from buf at the specified offsetand interprets the result as a little-endian, two's complement signed value supporting up to 48 bits of accuracy.

import { Buffer } from 'buffer';

const buf = Buffer.from([0x12, 0x34, 0x56, 0x78, 0x90, 0xab]);

console.log(buf.readIntLE(0, 6).toString(16));
// Prints: -546f87a9cbee
readUInt16BE(offset?: number): number

Reads an unsigned, big-endian 16-bit integer from buf at the specifiedoffset.

This function is also available under the readUint16BE alias.

import { Buffer } from 'buffer';

const buf = Buffer.from([0x12, 0x34, 0x56]);

console.log(buf.readUInt16BE(0).toString(16));
// Prints: 1234
console.log(buf.readUInt16BE(1).toString(16));
// Prints: 3456
readUInt16LE(offset?: number): number

Reads an unsigned, little-endian 16-bit integer from buf at the specifiedoffset.

This function is also available under the readUint16LE alias.

import { Buffer } from 'buffer';

const buf = Buffer.from([0x12, 0x34, 0x56]);

console.log(buf.readUInt16LE(0).toString(16));
// Prints: 3412
console.log(buf.readUInt16LE(1).toString(16));
// Prints: 5634
console.log(buf.readUInt16LE(2).toString(16));
// Throws ERR_OUT_OF_RANGE.
readUInt32BE(offset?: number): number

Reads an unsigned, big-endian 32-bit integer from buf at the specifiedoffset.

This function is also available under the readUint32BE alias.

import { Buffer } from 'buffer';

const buf = Buffer.from([0x12, 0x34, 0x56, 0x78]);

console.log(buf.readUInt32BE(0).toString(16));
// Prints: 12345678
readUInt32LE(offset?: number): number

Reads an unsigned, little-endian 32-bit integer from buf at the specifiedoffset.

This function is also available under the readUint32LE alias.

import { Buffer } from 'buffer';

const buf = Buffer.from([0x12, 0x34, 0x56, 0x78]);

console.log(buf.readUInt32LE(0).toString(16));
// Prints: 78563412
console.log(buf.readUInt32LE(1).toString(16));
// Throws ERR_OUT_OF_RANGE.
readUInt8(offset?: number): number

Reads an unsigned 8-bit integer from buf at the specified offset.

This function is also available under the readUint8 alias.

import { Buffer } from 'buffer';

const buf = Buffer.from([1, -2]);

console.log(buf.readUInt8(0));
// Prints: 1
console.log(buf.readUInt8(1));
// Prints: 254
console.log(buf.readUInt8(2));
// Throws ERR_OUT_OF_RANGE.
readUIntBE(offset: number, byteLength: number): number

Reads byteLength number of bytes from buf at the specified offsetand interprets the result as an unsigned big-endian integer supporting up to 48 bits of accuracy.

This function is also available under the readUintBE alias.

import { Buffer } from 'buffer';

const buf = Buffer.from([0x12, 0x34, 0x56, 0x78, 0x90, 0xab]);

console.log(buf.readUIntBE(0, 6).toString(16));
// Prints: 1234567890ab
console.log(buf.readUIntBE(1, 6).toString(16));
// Throws ERR_OUT_OF_RANGE.
readUIntLE(offset: number, byteLength: number): number

Reads byteLength number of bytes from buf at the specified offsetand interprets the result as an unsigned, little-endian integer supporting up to 48 bits of accuracy.

This function is also available under the readUintLE alias.

import { Buffer } from 'buffer';

const buf = Buffer.from([0x12, 0x34, 0x56, 0x78, 0x90, 0xab]);

console.log(buf.readUIntLE(0, 6).toString(16));
// Prints: ab9078563412
reverse(): this
slice(start?: number, end?: number): Buffer

Returns a new Buffer that references the same memory as the original, but offset and cropped by the start and end indices.

This is the same behavior as buf.subarray().

This method is not compatible with the Uint8Array.prototype.slice(), which is a superclass of Buffer. To copy the slice, useUint8Array.prototype.slice().

import { Buffer } from 'buffer';

const buf = Buffer.from('buffer');

const copiedBuf = Uint8Array.prototype.slice.call(buf);
copiedBuf[0]++;
console.log(copiedBuf.toString());
// Prints: cuffer

console.log(buf.toString());
// Prints: buffer
subarray(start?: number, end?: number): Buffer

Returns a new Buffer that references the same memory as the original, but offset and cropped by the start and end indices.

Specifying end greater than buf.length will return the same result as that of end equal to buf.length.

This method is inherited from TypedArray.prototype.subarray().

Modifying the new Buffer slice will modify the memory in the original Bufferbecause the allocated memory of the two objects overlap.

import { Buffer } from 'buffer';

// Create a `Buffer` with the ASCII alphabet, take a slice, and modify one byte
// from the original `Buffer`.

const buf1 = Buffer.allocUnsafe(26);

for (let i = 0; i < 26; i++) {
  // 97 is the decimal ASCII value for 'a'.
  buf1[i] = i + 97;
}

const buf2 = buf1.subarray(0, 3);

console.log(buf2.toString('ascii', 0, buf2.length));
// Prints: abc

buf1[0] = 33;

console.log(buf2.toString('ascii', 0, buf2.length));
// Prints: !bc

Specifying negative indexes causes the slice to be generated relative to the end of buf rather than the beginning.

import { Buffer } from 'buffer';

const buf = Buffer.from('buffer');

console.log(buf.subarray(-6, -1).toString());
// Prints: buffe
// (Equivalent to buf.subarray(0, 5).)

console.log(buf.subarray(-6, -2).toString());
// Prints: buff
// (Equivalent to buf.subarray(0, 4).)

console.log(buf.subarray(-5, -2).toString());
// Prints: uff
// (Equivalent to buf.subarray(1, 4).)
swap16(): Buffer

Interprets buf as an array of unsigned 16-bit integers and swaps the byte order in-place. Throws ERR_INVALID_BUFFER_SIZE if buf.length is not a multiple of 2.

import { Buffer } from 'buffer';

const buf1 = Buffer.from([0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8]);

console.log(buf1);
// Prints: <Buffer 01 02 03 04 05 06 07 08>

buf1.swap16();

console.log(buf1);
// Prints: <Buffer 02 01 04 03 06 05 08 07>

const buf2 = Buffer.from([0x1, 0x2, 0x3]);

buf2.swap16();
// Throws ERR_INVALID_BUFFER_SIZE.

One convenient use of buf.swap16() is to perform a fast in-place conversion between UTF-16 little-endian and UTF-16 big-endian:

import { Buffer } from 'buffer';

const buf = Buffer.from('This is little-endian UTF-16', 'utf16le');
buf.swap16(); // Convert to big-endian UTF-16 text.
swap32(): Buffer

Interprets buf as an array of unsigned 32-bit integers and swaps the byte order in-place. Throws ERR_INVALID_BUFFER_SIZE if buf.length is not a multiple of 4.

import { Buffer } from 'buffer';

const buf1 = Buffer.from([0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8]);

console.log(buf1);
// Prints: <Buffer 01 02 03 04 05 06 07 08>

buf1.swap32();

console.log(buf1);
// Prints: <Buffer 04 03 02 01 08 07 06 05>

const buf2 = Buffer.from([0x1, 0x2, 0x3]);

buf2.swap32();
// Throws ERR_INVALID_BUFFER_SIZE.
swap64(): Buffer

Interprets buf as an array of 64-bit numbers and swaps byte order in-place. Throws ERR_INVALID_BUFFER_SIZE if buf.length is not a multiple of 8.

import { Buffer } from 'buffer';

const buf1 = Buffer.from([0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8]);

console.log(buf1);
// Prints: <Buffer 01 02 03 04 05 06 07 08>

buf1.swap64();

console.log(buf1);
// Prints: <Buffer 08 07 06 05 04 03 02 01>

const buf2 = Buffer.from([0x1, 0x2, 0x3]);

buf2.swap64();
// Throws ERR_INVALID_BUFFER_SIZE.
toJSON(): { type: "Buffer"; data: number[]; }

Returns a JSON representation of buf. JSON.stringify() implicitly calls this function when stringifying a Buffer instance.

Buffer.from() accepts objects in the format returned from this method. In particular, Buffer.from(buf.toJSON()) works like Buffer.from(buf).

import { Buffer } from 'buffer';

const buf = Buffer.from([0x1, 0x2, 0x3, 0x4, 0x5]);
const json = JSON.stringify(buf);

console.log(json);
// Prints: {"type":"Buffer","data":[1,2,3,4,5]}

const copy = JSON.parse(json, (key, value) => {
  return value &#x26;&#x26; value.type === 'Buffer' ?
    Buffer.from(value) :
    value;
});

console.log(copy);
// Prints: <Buffer 01 02 03 04 05>
toString(
encoding?: Encoding,
start?: number,
end?: number,
): string

Decodes buf to a string according to the specified character encoding inencoding. start and end may be passed to decode only a subset of buf.

If encoding is 'utf8' and a byte sequence in the input is not valid UTF-8, then each invalid byte is replaced with the replacement character U+FFFD.

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

import { Buffer } from '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;
}

console.log(buf1.toString('utf8'));
// Prints: abcdefghijklmnopqrstuvwxyz
console.log(buf1.toString('utf8', 0, 5));
// Prints: abcde

const buf2 = Buffer.from('tést');

console.log(buf2.toString('hex'));
// Prints: 74c3a97374
console.log(buf2.toString('utf8', 0, 3));
// Prints: té
console.log(buf2.toString(undefined, 0, 3));
// Prints: té
values(): IterableIterator<number>

Creates and returns an iterator for buf values (bytes). This function is called automatically when a Buffer is used in a for..of statement.

import { Buffer } from 'buffer';

const buf = Buffer.from('buffer');

for (const value of buf.values()) {
  console.log(value);
}
// Prints:
//   98
//   117
//   102
//   102
//   101
//   114

for (const value of buf) {
  console.log(value);
}
// Prints:
//   98
//   117
//   102
//   102
//   101
//   114
write(string: string, encoding?: Encoding): number

Writes string to buf at offset according to the character encoding inencoding. The length parameter is the number of bytes to write. If buf did not contain enough space to fit the entire string, only part of string will be written. However, partially encoded characters will not be written.

import { Buffer } from 'buffer';

const buf = Buffer.alloc(256);

const len = buf.write('\u00bd + \u00bc = \u00be', 0);

console.log(`${len} bytes: ${buf.toString('utf8', 0, len)}`);
// Prints: 12 bytes: ½ + ¼ = ¾

const buffer = Buffer.alloc(10);

const length = buffer.write('abcd', 8);

console.log(`${length} bytes: ${buffer.toString('utf8', 8, 10)}`);
// Prints: 2 bytes : ab
write(
string: string,
offset: number,
encoding?: Encoding,
): number
write(
string: string,
offset: number,
length: number,
encoding?: Encoding,
): number
writeBigInt64BE(value: bigint, offset?: number): number

Writes value to buf at the specified offset as big-endian.

value is interpreted and written as a two's complement signed integer.

import { Buffer } from 'buffer';

const buf = Buffer.allocUnsafe(8);

buf.writeBigInt64BE(0x0102030405060708n, 0);

console.log(buf);
// Prints: <Buffer 01 02 03 04 05 06 07 08>
writeBigInt64LE(value: bigint, offset?: number): number

Writes value to buf at the specified offset as little-endian.

value is interpreted and written as a two's complement signed integer.

import { Buffer } from 'buffer';

const buf = Buffer.allocUnsafe(8);

buf.writeBigInt64LE(0x0102030405060708n, 0);

console.log(buf);
// Prints: <Buffer 08 07 06 05 04 03 02 01>
writeBigUInt64BE(value: bigint, offset?: number): number

Writes value to buf at the specified offset as big-endian.

This function is also available under the writeBigUint64BE alias.

import { Buffer } from 'buffer';

const buf = Buffer.allocUnsafe(8);

buf.writeBigUInt64BE(0xdecafafecacefaden, 0);

console.log(buf);
// Prints: <Buffer de ca fa fe ca ce fa de>
writeBigUInt64LE(value: bigint, offset?: number): number

Writes value to buf at the specified offset as little-endian

import { Buffer } from 'buffer';

const buf = Buffer.allocUnsafe(8);

buf.writeBigUInt64LE(0xdecafafecacefaden, 0);

console.log(buf);
// Prints: <Buffer de fa ce ca fe fa ca de>

This function is also available under the writeBigUint64LE alias.

writeDoubleBE(value: number, offset?: number): number

Writes value to buf at the specified offset as big-endian. The valuemust be a JavaScript number. Behavior is undefined when value is anything other than a JavaScript number.

import { Buffer } from 'buffer';

const buf = Buffer.allocUnsafe(8);

buf.writeDoubleBE(123.456, 0);

console.log(buf);
// Prints: <Buffer 40 5e dd 2f 1a 9f be 77>
writeDoubleLE(value: number, offset?: number): number

Writes value to buf at the specified offset as little-endian. The valuemust be a JavaScript number. Behavior is undefined when value is anything other than a JavaScript number.

import { Buffer } from 'buffer';

const buf = Buffer.allocUnsafe(8);

buf.writeDoubleLE(123.456, 0);

console.log(buf);
// Prints: <Buffer 77 be 9f 1a 2f dd 5e 40>
writeFloatBE(value: number, offset?: number): number

Writes value to buf at the specified offset as big-endian. Behavior is undefined when value is anything other than a JavaScript number.

import { Buffer } from 'buffer';

const buf = Buffer.allocUnsafe(4);

buf.writeFloatBE(0xcafebabe, 0);

console.log(buf);
// Prints: <Buffer 4f 4a fe bb>
writeFloatLE(value: number, offset?: number): number

Writes value to buf at the specified offset as little-endian. Behavior is undefined when value is anything other than a JavaScript number.

import { Buffer } from 'buffer';

const buf = Buffer.allocUnsafe(4);

buf.writeFloatLE(0xcafebabe, 0);

console.log(buf);
// Prints: <Buffer bb fe 4a 4f>
writeInt16BE(value: number, offset?: number): number

Writes value to buf at the specified offset as big-endian. The valuemust be a valid signed 16-bit integer. Behavior is undefined when value is anything other than a signed 16-bit integer.

The value is interpreted and written as a two's complement signed integer.

import { Buffer } from 'buffer';

const buf = Buffer.allocUnsafe(2);

buf.writeInt16BE(0x0102, 0);

console.log(buf);
// Prints: <Buffer 01 02>
writeInt16LE(value: number, offset?: number): number

Writes value to buf at the specified offset as little-endian. The valuemust be a valid signed 16-bit integer. Behavior is undefined when value is anything other than a signed 16-bit integer.

The value is interpreted and written as a two's complement signed integer.

import { Buffer } from 'buffer';

const buf = Buffer.allocUnsafe(2);

buf.writeInt16LE(0x0304, 0);

console.log(buf);
// Prints: <Buffer 04 03>
writeInt32BE(value: number, offset?: number): number

Writes value to buf at the specified offset as big-endian. The valuemust be a valid signed 32-bit integer. Behavior is undefined when value is anything other than a signed 32-bit integer.

The value is interpreted and written as a two's complement signed integer.

import { Buffer } from 'buffer';

const buf = Buffer.allocUnsafe(4);

buf.writeInt32BE(0x01020304, 0);

console.log(buf);
// Prints: <Buffer 01 02 03 04>
writeInt32LE(value: number, offset?: number): number

Writes value to buf at the specified offset as little-endian. The valuemust be a valid signed 32-bit integer. Behavior is undefined when value is anything other than a signed 32-bit integer.

The value is interpreted and written as a two's complement signed integer.

import { Buffer } from 'buffer';

const buf = Buffer.allocUnsafe(4);

buf.writeInt32LE(0x05060708, 0);

console.log(buf);
// Prints: <Buffer 08 07 06 05>
writeInt8(value: number, offset?: number): number

Writes value to buf at the specified offset. value must be a valid signed 8-bit integer. Behavior is undefined when value is anything other than a signed 8-bit integer.

value is interpreted and written as a two's complement signed integer.

import { Buffer } from 'buffer';

const buf = Buffer.allocUnsafe(2);

buf.writeInt8(2, 0);
buf.writeInt8(-2, 1);

console.log(buf);
// Prints: <Buffer 02 fe>
writeIntBE(
value: number,
offset: number,
byteLength: number,
): number

Writes byteLength bytes of value to buf at the specified offsetas big-endian. Supports up to 48 bits of accuracy. Behavior is undefined whenvalue is anything other than a signed integer.

import { Buffer } from 'buffer';

const buf = Buffer.allocUnsafe(6);

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

console.log(buf);
// Prints: <Buffer 12 34 56 78 90 ab>
writeIntLE(
value: number,
offset: number,
byteLength: number,
): number

Writes byteLength bytes of value to buf at the specified offsetas little-endian. Supports up to 48 bits of accuracy. Behavior is undefined when value is anything other than a signed integer.

import { Buffer } from 'buffer';

const buf = Buffer.allocUnsafe(6);

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

console.log(buf);
// Prints: <Buffer ab 90 78 56 34 12>
writeUInt16BE(value: number, offset?: number): number

Writes value to buf at the specified offset as big-endian. The valuemust be a valid unsigned 16-bit integer. Behavior is undefined when valueis anything other than an unsigned 16-bit integer.

This function is also available under the writeUint16BE alias.

import { Buffer } from 'buffer';

const buf = Buffer.allocUnsafe(4);

buf.writeUInt16BE(0xdead, 0);
buf.writeUInt16BE(0xbeef, 2);

console.log(buf);
// Prints: <Buffer de ad be ef>
writeUInt16LE(value: number, offset?: number): number

Writes value to buf at the specified offset as little-endian. The valuemust be a valid unsigned 16-bit integer. Behavior is undefined when value is anything other than an unsigned 16-bit integer.

This function is also available under the writeUint16LE alias.

import { Buffer } from 'buffer';

const buf = Buffer.allocUnsafe(4);

buf.writeUInt16LE(0xdead, 0);
buf.writeUInt16LE(0xbeef, 2);

console.log(buf);
// Prints: <Buffer ad de ef be>
writeUInt32BE(value: number, offset?: number): number

Writes value to buf at the specified offset as big-endian. The valuemust be a valid unsigned 32-bit integer. Behavior is undefined when valueis anything other than an unsigned 32-bit integer.

This function is also available under the writeUint32BE alias.

import { Buffer } from 'buffer';

const buf = Buffer.allocUnsafe(4);

buf.writeUInt32BE(0xfeedface, 0);

console.log(buf);
// Prints: <Buffer fe ed fa ce>
writeUInt32LE(value: number, offset?: number): number

Writes value to buf at the specified offset as little-endian. The valuemust be a valid unsigned 32-bit integer. Behavior is undefined when value is anything other than an unsigned 32-bit integer.

This function is also available under the writeUint32LE alias.

import { Buffer } from 'buffer';

const buf = Buffer.allocUnsafe(4);

buf.writeUInt32LE(0xfeedface, 0);

console.log(buf);
// Prints: <Buffer ce fa ed fe>
writeUInt8(value: number, offset?: number): number

Writes value to buf at the specified offset. value must be a valid unsigned 8-bit integer. Behavior is undefined when value is anything other than an unsigned 8-bit integer.

This function is also available under the writeUint8 alias.

import { Buffer } from 'buffer';

const buf = Buffer.allocUnsafe(4);

buf.writeUInt8(0x3, 0);
buf.writeUInt8(0x4, 1);
buf.writeUInt8(0x23, 2);
buf.writeUInt8(0x42, 3);

console.log(buf);
// Prints: <Buffer 03 04 23 42>
writeUIntBE(
value: number,
offset: number,
byteLength: number,
): number

Writes byteLength bytes of value to buf at the specified offsetas big-endian. Supports up to 48 bits of accuracy. Behavior is undefined when value is anything other than an unsigned integer.

This function is also available under the writeUintBE alias.

import { Buffer } from 'buffer';

const buf = Buffer.allocUnsafe(6);

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

console.log(buf);
// Prints: <Buffer 12 34 56 78 90 ab>
writeUIntLE(
value: number,
offset: number,
byteLength: number,
): number

Writes byteLength bytes of value to buf at the specified offsetas little-endian. Supports up to 48 bits of accuracy. Behavior is undefined when value is anything other than an unsigned integer.

This function is also available under the writeUintLE alias.

import { Buffer } from 'buffer';

const buf = Buffer.allocUnsafe(6);

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

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

Static Methods

alloc(
size: number,
fill?: string | Uint8Array | number,
encoding?: Encoding,
): Buffer

Allocates a new Buffer of size bytes. If fill is undefined, theBuffer will be zero-filled.

import { Buffer } from 'buffer';

const buf = Buffer.alloc(5);

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

If size is larger than {@link constants.MAX_LENGTH} or smaller than 0, ERR_INVALID_ARG_VALUE is thrown.

If fill is specified, the allocated Buffer will be initialized by calling buf.fill(fill).

import { Buffer } from 'buffer';

const buf = Buffer.alloc(5, 'a');

console.log(buf);
// Prints: <Buffer 61 61 61 61 61>

If both fill and encoding are specified, the allocated Buffer will be initialized by calling buf.fill(fill, encoding).

import { Buffer } from 'buffer';

const buf = Buffer.alloc(11, 'aGVsbG8gd29ybGQ=', 'base64');

console.log(buf);
// Prints: <Buffer 68 65 6c 6c 6f 20 77 6f 72 6c 64>

Calling Buffer.alloc() can be measurably slower than the alternative Buffer.allocUnsafe() but ensures that the newly created Buffer instance contents will never contain sensitive data from previous allocations, including data that might not have been allocated for Buffers.

A TypeError will be thrown if size is not a number.

allocUnsafe(size: number): Buffer

Allocates a new Buffer of size bytes. If size is larger than {@link constants.MAX_LENGTH} or smaller than 0, ERR_INVALID_ARG_VALUE is thrown.

The underlying memory for Buffer instances created in this way is not initialized. The contents of the newly created Buffer are unknown and_may contain sensitive data_. Use Buffer.alloc() instead to initializeBuffer instances with zeroes.

import { Buffer } from 'buffer';

const buf = Buffer.allocUnsafe(10);

console.log(buf);
// Prints (contents may vary): <Buffer a0 8b 28 3f 01 00 00 00 50 32>

buf.fill(0);

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

A TypeError will be thrown if size is not a number.

The Buffer module pre-allocates an internal Buffer instance of size Buffer.poolSize that is used as a pool for the fast allocation of newBuffer instances created using Buffer.allocUnsafe(),Buffer.from(array), Buffer.concat(), and the deprecatednew 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 Bufferpool, while Buffer.allocUnsafe(size).fill(fill)_will_ use the internalBuffer 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.

allocUnsafeSlow(size: number): Buffer

Allocates a new Buffer of size bytes. If size is larger than {@link constants.MAX_LENGTH} or smaller than 0, ERR_INVALID_ARG_VALUE is thrown. A zero-length Buffer is created if size is 0.

The underlying memory for Buffer instances created in this way is not initialized. The contents of the newly created Buffer are unknown and_may contain sensitive data_. Use buf.fill(0) to initialize such Buffer instances with zeroes.

When using Buffer.allocUnsafe() to allocate new Buffer instances, allocations under 4 KB are sliced from a single pre-allocated Buffer. This allows applications to avoid the garbage collection overhead of creating many individually allocated Buffer instances. This approach improves both performance and memory usage by eliminating the need to track and clean up as many individual ArrayBuffer objects.

However, in the case where a developer may need to retain a small chunk of memory from a pool for an indeterminate amount of time, it may be appropriate to create an un-pooled Buffer instance using Buffer.allocUnsafeSlow() and then copying out the relevant bits.

import { Buffer } from 'buffer';

// Need to keep around a few small chunks of memory.
const store = [];

socket.on('readable', () => {
  let data;
  while (null !== (data = readable.read())) {
    // Allocate for retained data.
    const sb = Buffer.allocUnsafeSlow(10);

    // Copy the data into the new allocation.
    data.copy(sb, 0, 0, 10);

    store.push(sb);
  }
});

A TypeError will be thrown if size is not a number.

byteLength(string:
| string
| ArrayBufferView
| ArrayBuffer
| SharedArrayBuffer
, encoding?: Encoding
): number

Returns the byte length of a string when encoded using encoding. This is not the same as String.prototype.length, which does not account for the encoding that is used to convert the string into bytes.

For 'base64', 'base64url', 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.

import { Buffer } from 'buffer';

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

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

When string is a Buffer/DataView/[TypedArray](https://developer.mozilla.org/en-US/docs/Web/JavaScript/- Reference/Global_Objects/TypedArray)/ArrayBuffer/[SharedArrayBuffer](https://develop- er.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/SharedArrayBuffer), the byte length as reported by .byteLengthis returned.

compare(buf1: Uint8Array, buf2: Uint8Array): number

Compares buf1 to buf2, typically for the purpose of sorting arrays ofBuffer instances. This is equivalent to calling buf1.compare(buf2).

import { Buffer } from 'buffer';

const buf1 = Buffer.from('1234');
const buf2 = Buffer.from('0123');
const arr = [buf1, buf2];

console.log(arr.sort(Buffer.compare));
// Prints: [ <Buffer 30 31 32 33>, <Buffer 31 32 33 34> ]
// (This result is equal to: [buf2, buf1].)
concat(list: ReadonlyArray<Uint8Array>, totalLength?: number): Buffer

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

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

If totalLength is not provided, it is calculated from the Buffer instances in list by adding their lengths.

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

import { Buffer } from 'buffer';

// Create a single `Buffer` from a list of three `Buffer` instances.

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

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

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

console.log(bufA);
// Prints: <Buffer 00 00 00 00 ...>
console.log(bufA.length);
// Prints: 42

Buffer.concat() may also use the internal Buffer pool like Buffer.allocUnsafe() does.

from(
arrayBuffer: WithImplicitCoercion<ArrayBuffer | SharedArrayBuffer>,
byteOffset?: number,
length?: number,
): Buffer

Allocates a new Buffer using an array of bytes in the range 0255. Array entries outside that range will be truncated to fit into it.

import { Buffer } from 'buffer';

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

A TypeError will be thrown if array is not an Array or another type appropriate for Buffer.from() variants.

Buffer.from(array) and Buffer.from(string) may also use the internalBuffer pool like Buffer.allocUnsafe() does.

from(data: Uint8Array | ReadonlyArray<number>): Buffer

Creates a new Buffer using the passed {data}

from(data: WithImplicitCoercion<Uint8Array | ReadonlyArray<number> | string>): Buffer
from(str: WithImplicitCoercion<string> | { [[Symbol.toPrimitive]](hint: "string"): string; }, encoding?: Encoding): Buffer

Creates a new Buffer containing the given JavaScript string {str}. If provided, the {encoding} parameter identifies the character encoding. If not provided, {encoding} defaults to 'utf8'.

isBuffer(obj: unknown): obj is Buffer

Returns true if obj is a Buffer, false otherwise.

import { Buffer } from 'buffer';

Buffer.isBuffer(Buffer.alloc(10)); // true
Buffer.isBuffer(Buffer.from('foo')); // true
Buffer.isBuffer('a string'); // false
Buffer.isBuffer([]); // false
Buffer.isBuffer(new Uint8Array(1024)); // false
isEncoding(encoding: string): boolean

Returns true if encoding is the name of a supported character encoding, or false otherwise.

import { Buffer } from 'buffer';

console.log(Buffer.isEncoding('utf8'));
// Prints: true

console.log(Buffer.isEncoding('hex'));
// Prints: true

console.log(Buffer.isEncoding('utf/8'));
// Prints: false

console.log(Buffer.isEncoding(''));
// Prints: false
of(...items: number[]): Buffer

Creates a new Buffer using the passed {data}