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Showing content from https://nodejs.org/dist/latest/docs/api/buffer.html below:

Buffer | Node.js v24.6.0 Documentation

Buffer#

Source Code: lib/buffer.js

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 'node:buffer';


const buf1 = Buffer.alloc(10);



const buf2 = Buffer.alloc(10, 1);






const buf3 = Buffer.allocUnsafe(10);


const buf4 = Buffer.from([1, 2, 3]);



const buf5 = Buffer.from([257, 257.5, -255, '1']);




const buf6 = Buffer.from('tést');


const buf7 = Buffer.from('tést', 'latin1');const { Buffer } = require('node:buffer');


const buf1 = Buffer.alloc(10);



const buf2 = Buffer.alloc(10, 1);






const buf3 = Buffer.allocUnsafe(10);


const buf4 = Buffer.from([1, 2, 3]);



const buf5 = Buffer.from([257, 257.5, -255, '1']);




const buf6 = Buffer.from('tést');


const buf7 = Buffer.from('tést', 'latin1');
Buffers and character encodings#

When converting between Buffers and strings, a character encoding may be specified. If no character encoding is specified, UTF-8 will be used as the default.

import { Buffer } from 'node:buffer';

const buf = Buffer.from('hello world', 'utf8');

console.log(buf.toString('hex'));

console.log(buf.toString('base64'));


console.log(Buffer.from('fhqwhgads', 'utf8'));

console.log(Buffer.from('fhqwhgads', 'utf16le'));
const { Buffer } = require('node:buffer');

const buf = Buffer.from('hello world', 'utf8');

console.log(buf.toString('hex'));

console.log(buf.toString('base64'));


console.log(Buffer.from('fhqwhgads', 'utf8'));

console.log(Buffer.from('fhqwhgads', 'utf16le'));

Node.js buffers accept all case variations of encoding strings that they receive. For example, UTF-8 can be specified as 'utf8', 'UTF8', or 'uTf8'.

The character encodings currently supported by Node.js are the following:

Converting a Buffer into a string using one of the above is referred to as decoding, and converting a string into a Buffer is referred to as encoding.

Node.js also supports the following binary-to-text encodings. For binary-to-text encodings, the naming convention is reversed: Converting a Buffer into a string is typically referred to as encoding, and converting a string into a Buffer as decoding.

The following legacy character encodings are also supported:

import { Buffer } from 'node:buffer';

Buffer.from('1ag123', 'hex');



Buffer.from('1a7', 'hex');


Buffer.from('1634', 'hex');
const { Buffer } = require('node:buffer');

Buffer.from('1ag123', 'hex');



Buffer.from('1a7', 'hex');


Buffer.from('1634', 'hex');

Modern Web browsers follow the WHATWG Encoding Standard which aliases both 'latin1' and 'ISO-8859-1' to 'win-1252'. This means that while doing something like http.get(), if the returned charset is one of those listed in the WHATWG specification it is possible that the server actually returned 'win-1252'-encoded data, and using 'latin1' encoding may incorrectly decode the characters.

Buffers and TypedArrays#

Buffer instances are also JavaScript <Uint8Array> and <TypedArray> instances. All <TypedArray> methods are available on Buffers. There are, however, subtle incompatibilities between the Buffer API and the <TypedArray> API.

In particular:

There are two ways to create new <TypedArray> instances from a Buffer:

import { Buffer } from 'node:buffer';

const buf = Buffer.from([1, 2, 3, 4]);
const uint32array = new Uint32Array(buf);

console.log(uint32array);

const { Buffer } = require('node:buffer');

const buf = Buffer.from([1, 2, 3, 4]);
const uint32array = new Uint32Array(buf);

console.log(uint32array);


import { Buffer } from 'node:buffer';

const buf = Buffer.from('hello', 'utf16le');
const uint16array = new Uint16Array(
  buf.buffer,
  buf.byteOffset,
  buf.length / Uint16Array.BYTES_PER_ELEMENT);

console.log(uint16array);

const { Buffer } = require('node:buffer');

const buf = Buffer.from('hello', 'utf16le');
const uint16array = new Uint16Array(
  buf.buffer,
  buf.byteOffset,
  buf.length / Uint16Array.BYTES_PER_ELEMENT);

console.log(uint16array);

It is possible to create a new Buffer that shares the same allocated memory as a <TypedArray> instance by using the TypedArray object's .buffer property in the same way. Buffer.from() behaves like new Uint8Array() in this context.

import { Buffer } from 'node:buffer';

const arr = new Uint16Array(2);

arr[0] = 5000;
arr[1] = 4000;


const buf1 = Buffer.from(arr);


const buf2 = Buffer.from(arr.buffer);

console.log(buf1);

console.log(buf2);


arr[1] = 6000;

console.log(buf1);

console.log(buf2);
const { Buffer } = require('node:buffer');

const arr = new Uint16Array(2);

arr[0] = 5000;
arr[1] = 4000;


const buf1 = Buffer.from(arr);


const buf2 = Buffer.from(arr.buffer);

console.log(buf1);

console.log(buf2);


arr[1] = 6000;

console.log(buf1);

console.log(buf2);

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.

import { Buffer } from 'node:buffer';

const arr = new Uint16Array(20);
const buf = Buffer.from(arr.buffer, 0, 16);

console.log(buf.length);
const { Buffer } = require('node:buffer');

const arr = new Uint16Array(20);
const buf = Buffer.from(arr.buffer, 0, 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:

The Buffer.from() method, however, does not support the use of a mapping function:

Buffers and iteration#

Buffer instances can be iterated over using for..of syntax:

import { Buffer } from 'node:buffer';

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

for (const b of buf) {
  console.log(b);
}



const { Buffer } = require('node:buffer');

const buf = Buffer.from([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: Blob#

A <Blob> encapsulates immutable, raw data that can be safely shared across multiple worker threads.

new buffer.Blob([sources[, options]])#

Creates a new Blob object containing a concatenation of the given sources.

<ArrayBuffer>, <TypedArray>, <DataView>, and <Buffer> sources are copied into the 'Blob' and can therefore be safely modified after the 'Blob' is created.

String sources are encoded as UTF-8 byte sequences and copied into the Blob. Unmatched surrogate pairs within each string part will be replaced by Unicode U+FFFD replacement characters.

blob.arrayBuffer()#

Added in: v15.7.0, v14.18.0

Returns a promise that fulfills with an <ArrayBuffer> containing a copy of the Blob data.

blob.bytes()#

Added in: v22.3.0, v20.16.0

The blob.bytes() method returns the byte of the Blob object as a Promise<Uint8Array>.

const blob = new Blob(['hello']);
blob.bytes().then((bytes) => {
  console.log(bytes); 
});
blob.size#

Added in: v15.7.0, v14.18.0

The total size of the Blob in bytes.

blob.slice([start[, end[, type]]])#

Added in: v15.7.0, v14.18.0

Creates and returns a new Blob containing a subset of this Blob objects data. The original Blob is not altered.

blob.stream()#

Added in: v16.7.0

Returns a new ReadableStream that allows the content of the Blob to be read.

blob.text()#

Added in: v15.7.0, v14.18.0

Returns a promise that fulfills with the contents of the Blob decoded as a UTF-8 string.

blob.type#

Added in: v15.7.0, v14.18.0

The content-type of the Blob.

Blob objects and MessageChannel#

Once a <Blob> object is created, it can be sent via MessagePort to multiple destinations without transferring or immediately copying the data. The data contained by the Blob is copied only when the arrayBuffer() or text() methods are called.

import { Blob } from 'node:buffer';
import { setTimeout as delay } from 'node:timers/promises';

const blob = new Blob(['hello there']);

const mc1 = new MessageChannel();
const mc2 = new MessageChannel();

mc1.port1.onmessage = async ({ data }) => {
  console.log(await data.arrayBuffer());
  mc1.port1.close();
};

mc2.port1.onmessage = async ({ data }) => {
  await delay(1000);
  console.log(await data.arrayBuffer());
  mc2.port1.close();
};

mc1.port2.postMessage(blob);
mc2.port2.postMessage(blob);


blob.text().then(console.log);const { Blob } = require('node:buffer');
const { setTimeout: delay } = require('node:timers/promises');

const blob = new Blob(['hello there']);

const mc1 = new MessageChannel();
const mc2 = new MessageChannel();

mc1.port1.onmessage = async ({ data }) => {
  console.log(await data.arrayBuffer());
  mc1.port1.close();
};

mc2.port1.onmessage = async ({ data }) => {
  await delay(1000);
  console.log(await data.arrayBuffer());
  mc2.port1.close();
};

mc1.port2.postMessage(blob);
mc2.port2.postMessage(blob);


blob.text().then(console.log);
Class: Buffer#

The Buffer class is a global type for dealing with binary data directly. It can be constructed in a variety of ways.

Static method: Buffer.alloc(size[, fill[, encoding]])#

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

import { Buffer } from 'node:buffer';

const buf = Buffer.alloc(5);

console.log(buf);
const { Buffer } = require('node:buffer');

const buf = Buffer.alloc(5);

console.log(buf);

If size is larger than buffer.constants.MAX_LENGTH or smaller than 0, ERR_OUT_OF_RANGE is thrown.

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

import { Buffer } from 'node:buffer';

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

console.log(buf);
const { Buffer } = require('node:buffer');

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

console.log(buf);

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

import { Buffer } from 'node:buffer';

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

console.log(buf);
const { Buffer } = require('node:buffer');

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

console.log(buf);

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.

Static method: Buffer.allocUnsafe(size)#

Allocates a new Buffer of size bytes. If size is larger than buffer.constants.MAX_LENGTH or smaller than 0, ERR_OUT_OF_RANGE is thrown.

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

import { Buffer } from 'node:buffer';

const buf = Buffer.allocUnsafe(10);

console.log(buf);


buf.fill(0);

console.log(buf);
const { Buffer } = require('node:buffer');

const buf = Buffer.allocUnsafe(10);

console.log(buf);


buf.fill(0);

console.log(buf);

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

The Buffer module pre-allocates an internal Buffer instance of size Buffer.poolSize that is used as a pool for the fast allocation of new Buffer instances created using Buffer.allocUnsafe(), Buffer.from(array), Buffer.from(string), and Buffer.concat() only when size is less than Buffer.poolSize >>> 1 (floor of Buffer.poolSize divided by two).

Use of this pre-allocated internal memory pool is a key difference between calling Buffer.alloc(size, fill) vs. Buffer.allocUnsafe(size).fill(fill). Specifically, Buffer.alloc(size, fill) will never use the internal Buffer pool, while Buffer.allocUnsafe(size).fill(fill) will use the internal Buffer pool if size is less than or equal to half Buffer.poolSize. The difference is subtle but can be important when an application requires the additional performance that Buffer.allocUnsafe() provides.

Static method: Buffer.allocUnsafeSlow(size)#

Allocates a new Buffer of size bytes. If size is larger than buffer.constants.MAX_LENGTH or smaller than 0, ERR_OUT_OF_RANGE 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 less than Buffer.poolSize >>> 1 (4KiB when default poolSize is used) 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 'node:buffer';


const store = [];

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

    
    data.copy(sb, 0, 0, 10);

    store.push(sb);
  }
});const { Buffer } = require('node:buffer');


const store = [];

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

    
    data.copy(sb, 0, 0, 10);

    store.push(sb);
  }
});

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

Static method: Buffer.byteLength(string[, encoding])#

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 'node:buffer';

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

console.log(`${str}: ${str.length} characters, ` +
            `${Buffer.byteLength(str, 'utf8')} bytes`);
const { Buffer } = require('node:buffer');

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

console.log(`${str}: ${str.length} characters, ` +
            `${Buffer.byteLength(str, 'utf8')} bytes`);

When string is a <Buffer> | <DataView> | <TypedArray> | <ArrayBuffer> | <SharedArrayBuffer>, the byte length as reported by .byteLength is returned.

Static method: Buffer.compare(buf1, buf2)#

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

import { Buffer } from 'node:buffer';

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

console.log(arr.sort(Buffer.compare));

const { Buffer } = require('node:buffer');

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

console.log(arr.sort(Buffer.compare));
Static method: Buffer.concat(list[, totalLength])#

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

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

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

If totalLength is provided, it is coerced to an unsigned integer. If the combined length of the Buffers in list exceeds totalLength, the result is truncated to totalLength. If the combined length of the Buffers in list is less than totalLength, the remaining space is filled with zeros.

import { Buffer } from 'node:buffer';



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);


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

console.log(bufA);

console.log(bufA.length);
const { Buffer } = require('node:buffer');



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);


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

console.log(bufA);

console.log(bufA.length);

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

Static method: Buffer.copyBytesFrom(view[, offset[, length]])#

Added in: v19.8.0, v18.16.0

Copies the underlying memory of view into a new Buffer.

const u16 = new Uint16Array([0, 0xffff]);
const buf = Buffer.copyBytesFrom(u16, 1, 1);
u16[1] = 0;
console.log(buf.length); 
console.log(buf[0]); 
console.log(buf[1]);
Static method: Buffer.from(array)#

Added in: v5.10.0

Allocates a new Buffer using an array of bytes in the range 0 – 255. Array entries outside that range will be truncated to fit into it.

import { Buffer } from 'node:buffer';


const buf = Buffer.from([0x62, 0x75, 0x66, 0x66, 0x65, 0x72]);const { Buffer } = require('node:buffer');


const buf = Buffer.from([0x62, 0x75, 0x66, 0x66, 0x65, 0x72]);

If array is an Array-like object (that is, one with a length property of type number), it is treated as if it is an array, unless it is a Buffer or a Uint8Array. This means all other TypedArray variants get treated as an Array. To create a Buffer from the bytes backing a TypedArray, use Buffer.copyBytesFrom().

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

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

Static method: Buffer.from(arrayBuffer[, byteOffset[, length]])#

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>'s underlying ArrayBuffer.

import { Buffer } from 'node:buffer';

const arr = new Uint16Array(2);

arr[0] = 5000;
arr[1] = 4000;


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

console.log(buf);



arr[1] = 6000;

console.log(buf);
const { Buffer } = require('node:buffer');

const arr = new Uint16Array(2);

arr[0] = 5000;
arr[1] = 4000;


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

console.log(buf);



arr[1] = 6000;

console.log(buf);

The optional byteOffset and length arguments specify a memory range within the arrayBuffer that will be shared by the Buffer.

import { Buffer } from 'node:buffer';

const ab = new ArrayBuffer(10);
const buf = Buffer.from(ab, 0, 2);

console.log(buf.length);
const { Buffer } = require('node:buffer');

const ab = new ArrayBuffer(10);
const buf = Buffer.from(ab, 0, 2);

console.log(buf.length);

A TypeError will be thrown if arrayBuffer is not an <ArrayBuffer> or a <SharedArrayBuffer> or another type appropriate for Buffer.from() variants.

It is important to remember that a backing ArrayBuffer can cover a range of memory that extends beyond the bounds of a TypedArray view. A new Buffer created using the buffer property of a TypedArray may extend beyond the range of the TypedArray:

import { Buffer } from 'node:buffer';

const arrA = Uint8Array.from([0x63, 0x64, 0x65, 0x66]); 
const arrB = new Uint8Array(arrA.buffer, 1, 2); 
console.log(arrA.buffer === arrB.buffer); 

const buf = Buffer.from(arrB.buffer);
console.log(buf);
const { Buffer } = require('node:buffer');

const arrA = Uint8Array.from([0x63, 0x64, 0x65, 0x66]); 
const arrB = new Uint8Array(arrA.buffer, 1, 2); 
console.log(arrA.buffer === arrB.buffer); 

const buf = Buffer.from(arrB.buffer);
console.log(buf);
Static method: Buffer.from(buffer)#

Added in: v5.10.0

Copies the passed buffer data onto a new Buffer instance.

import { Buffer } from 'node:buffer';

const buf1 = Buffer.from('buffer');
const buf2 = Buffer.from(buf1);

buf1[0] = 0x61;

console.log(buf1.toString());

console.log(buf2.toString());
const { Buffer } = require('node:buffer');

const buf1 = Buffer.from('buffer');
const buf2 = Buffer.from(buf1);

buf1[0] = 0x61;

console.log(buf1.toString());

console.log(buf2.toString());

A TypeError will be thrown if buffer is not a Buffer or another type appropriate for Buffer.from() variants.

Static method: Buffer.from(object[, offsetOrEncoding[, length]])#

Added in: v8.2.0

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

import { Buffer } from 'node:buffer';

const buf = Buffer.from(new String('this is a test'));
const { Buffer } = require('node:buffer');

const buf = Buffer.from(new String('this is a test'));

For objects that support Symbol.toPrimitive, returns Buffer.from(object[Symbol.toPrimitive]('string'), offsetOrEncoding).

import { Buffer } from 'node:buffer';

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

const buf = Buffer.from(new Foo(), 'utf8');
const { Buffer } = require('node:buffer');

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

const buf = Buffer.from(new Foo(), 'utf8');

A TypeError will be thrown if object does not have the mentioned methods or is not of another type appropriate for Buffer.from() variants.

Static method: Buffer.from(string[, encoding])#

Added in: v5.10.0

Creates a new Buffer containing string. The encoding parameter identifies the character encoding to be used when converting string into bytes.

import { Buffer } from 'node:buffer';

const buf1 = Buffer.from('this is a tést');
const buf2 = Buffer.from('7468697320697320612074c3a97374', 'hex');

console.log(buf1.toString());

console.log(buf2.toString());

console.log(buf1.toString('latin1'));
const { Buffer } = require('node:buffer');

const buf1 = Buffer.from('this is a tést');
const buf2 = Buffer.from('7468697320697320612074c3a97374', 'hex');

console.log(buf1.toString());

console.log(buf2.toString());

console.log(buf1.toString('latin1'));

A TypeError will be thrown if string is not a string or another type appropriate for Buffer.from() variants.

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

Static method: Buffer.isBuffer(obj)#

Added in: v0.1.101

Returns true if obj is a Buffer, false otherwise.

import { Buffer } from 'node:buffer';

Buffer.isBuffer(Buffer.alloc(10)); 
Buffer.isBuffer(Buffer.from('foo')); 
Buffer.isBuffer('a string'); 
Buffer.isBuffer([]); 
Buffer.isBuffer(new Uint8Array(1024)); const { Buffer } = require('node:buffer');

Buffer.isBuffer(Buffer.alloc(10)); 
Buffer.isBuffer(Buffer.from('foo')); 
Buffer.isBuffer('a string'); 
Buffer.isBuffer([]); 
Buffer.isBuffer(new Uint8Array(1024));
Static method: Buffer.isEncoding(encoding)#

Added in: v0.9.1

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

import { Buffer } from 'node:buffer';

console.log(Buffer.isEncoding('utf8'));


console.log(Buffer.isEncoding('hex'));


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


console.log(Buffer.isEncoding(''));
const { Buffer } = require('node:buffer');

console.log(Buffer.isEncoding('utf8'));


console.log(Buffer.isEncoding('hex'));


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


console.log(Buffer.isEncoding(''));
Class property: Buffer.poolSize#

Added in: v0.11.3

This is the size (in bytes) 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. In other words, buf[index] returns undefined when index is negative or greater or equal to buf.length, and buf[index] = value does not modify the buffer if index is negative or >= buf.length.

import { Buffer } from 'node:buffer';





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

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

console.log(buf.toString('utf8'));
const { Buffer } = require('node:buffer');





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

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

console.log(buf.toString('utf8'));
buf.buffer#

This ArrayBuffer is not guaranteed to correspond exactly to the original Buffer. See the notes on buf.byteOffset for details.

import { Buffer } from 'node:buffer';

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

console.log(buffer.buffer === arrayBuffer);
const { Buffer } = require('node:buffer');

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

console.log(buffer.buffer === arrayBuffer);
buf.byteOffset#

When setting byteOffset in Buffer.from(ArrayBuffer, byteOffset, length), or sometimes when allocating a Buffer smaller than Buffer.poolSize, the buffer does not start from a zero offset on the underlying ArrayBuffer.

This can cause problems when accessing the underlying ArrayBuffer directly using buf.buffer, as other parts of the ArrayBuffer may be unrelated to the Buffer object itself.

A common issue when creating a TypedArray object that shares its memory with a Buffer is that in this case one needs to specify the byteOffset correctly:

import { Buffer } from 'node:buffer';


const nodeBuffer = Buffer.from([0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);




new Int8Array(nodeBuffer.buffer, nodeBuffer.byteOffset, nodeBuffer.length);const { Buffer } = require('node:buffer');


const nodeBuffer = Buffer.from([0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);




new Int8Array(nodeBuffer.buffer, nodeBuffer.byteOffset, nodeBuffer.length);
buf.compare(target[, targetStart[, targetEnd[, sourceStart[, sourceEnd]]]])#

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.

import { Buffer } from 'node:buffer';

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

console.log(buf1.compare(buf1));

console.log(buf1.compare(buf2));

console.log(buf1.compare(buf3));

console.log(buf2.compare(buf1));

console.log(buf2.compare(buf3));

console.log([buf1, buf2, buf3].sort(Buffer.compare));

const { Buffer } = require('node:buffer');

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

console.log(buf1.compare(buf1));

console.log(buf1.compare(buf2));

console.log(buf1.compare(buf3));

console.log(buf2.compare(buf1));

console.log(buf2.compare(buf3));

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.

import { Buffer } from 'node: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));

console.log(buf1.compare(buf2, 0, 6, 4));

console.log(buf1.compare(buf2, 5, 6, 5));
const { Buffer } = require('node: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));

console.log(buf1.compare(buf2, 0, 6, 4));

console.log(buf1.compare(buf2, 5, 6, 5));

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

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

Added in: v0.1.90

Copies data from a region of buf to a region in target, even if the target memory 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 'node:buffer';


const buf1 = Buffer.allocUnsafe(26);
const buf2 = Buffer.allocUnsafe(26).fill('!');

for (let i = 0; i < 26; i++) {
  
  buf1[i] = i + 97;
}


buf1.copy(buf2, 8, 16, 20);



console.log(buf2.toString('ascii', 0, 25));
const { Buffer } = require('node:buffer');


const buf1 = Buffer.allocUnsafe(26);
const buf2 = Buffer.allocUnsafe(26).fill('!');

for (let i = 0; i < 26; i++) {
  
  buf1[i] = i + 97;
}


buf1.copy(buf2, 8, 16, 20);



console.log(buf2.toString('ascii', 0, 25));

import { Buffer } from 'node:buffer';




const buf = Buffer.allocUnsafe(26);

for (let i = 0; i < 26; i++) {
  
  buf[i] = i + 97;
}

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

console.log(buf.toString());
const { Buffer } = require('node:buffer');




const buf = Buffer.allocUnsafe(26);

for (let i = 0; i < 26; i++) {
  
  buf[i] = i + 97;
}

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

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.

import { Buffer } from 'node:buffer';



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

for (const pair of buf.entries()) {
  console.log(pair);
}






const { Buffer } = require('node:buffer');



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

for (const pair of buf.entries()) {
  console.log(pair);
}
buf.equals(otherBuffer)#

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

import { Buffer } from 'node:buffer';

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

console.log(buf1.equals(buf2));

console.log(buf1.equals(buf3));
const { Buffer } = require('node:buffer');

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

console.log(buf1.equals(buf2));

console.log(buf1.equals(buf3));
buf.fill(value[, offset[, end]][, encoding])#

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

import { Buffer } from 'node:buffer';



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

console.log(b.toString());



const c = Buffer.allocUnsafe(5).fill('');

console.log(c.fill(''));
const { Buffer } = require('node:buffer');



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

console.log(b.toString());



const c = Buffer.allocUnsafe(5).fill('');

console.log(c.fill(''));

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

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

import { Buffer } from 'node:buffer';



console.log(Buffer.allocUnsafe(5).fill('\u0222'));
const { Buffer } = require('node:buffer');



console.log(Buffer.allocUnsafe(5).fill('\u0222'));

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

import { Buffer } from 'node:buffer';

const buf = Buffer.allocUnsafe(5);

console.log(buf.fill('a'));

console.log(buf.fill('aazz', 'hex'));

console.log(buf.fill('zz', 'hex'));
const { Buffer } = require('node:buffer');

const buf = Buffer.allocUnsafe(5);

console.log(buf.fill('a'));

console.log(buf.fill('aazz', 'hex'));

console.log(buf.fill('zz', 'hex'));
buf.includes(value[, byteOffset][, encoding])#

Added in: v5.3.0

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

import { Buffer } from 'node:buffer';

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

console.log(buf.includes('this'));

console.log(buf.includes('is'));

console.log(buf.includes(Buffer.from('a buffer')));

console.log(buf.includes(97));

console.log(buf.includes(Buffer.from('a buffer example')));

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

console.log(buf.includes('this', 4));
const { Buffer } = require('node:buffer');

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

console.log(buf.includes('this'));

console.log(buf.includes('is'));

console.log(buf.includes(Buffer.from('a buffer')));

console.log(buf.includes(97));

console.log(buf.includes(Buffer.from('a buffer example')));

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

console.log(buf.includes('this', 4));
buf.indexOf(value[, byteOffset][, encoding])#

If value is:

import { Buffer } from 'node:buffer';

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

console.log(buf.indexOf('this'));

console.log(buf.indexOf('is'));

console.log(buf.indexOf(Buffer.from('a buffer')));

console.log(buf.indexOf(97));

console.log(buf.indexOf(Buffer.from('a buffer example')));

console.log(buf.indexOf(Buffer.from('a buffer example').slice(0, 8)));


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

console.log(utf16Buffer.indexOf('\u03a3', 0, 'utf16le'));

console.log(utf16Buffer.indexOf('\u03a3', -4, 'utf16le'));
const { Buffer } = require('node:buffer');

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

console.log(buf.indexOf('this'));

console.log(buf.indexOf('is'));

console.log(buf.indexOf(Buffer.from('a buffer')));

console.log(buf.indexOf(97));

console.log(buf.indexOf(Buffer.from('a buffer example')));

console.log(buf.indexOf(Buffer.from('a buffer example').slice(0, 8)));


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

console.log(utf16Buffer.indexOf('\u03a3', 0, 'utf16le'));

console.log(utf16Buffer.indexOf('\u03a3', -4, 'utf16le'));

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

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

import { Buffer } from 'node:buffer';

const b = Buffer.from('abcdef');



console.log(b.indexOf(99.9));
console.log(b.indexOf(256 + 99));



console.log(b.indexOf('b', undefined));
console.log(b.indexOf('b', {}));
console.log(b.indexOf('b', null));
console.log(b.indexOf('b', []));const { Buffer } = require('node:buffer');

const b = Buffer.from('abcdef');



console.log(b.indexOf(99.9));
console.log(b.indexOf(256 + 99));



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 (indexes).

import { Buffer } from 'node:buffer';

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

for (const key of buf.keys()) {
  console.log(key);
}






const { Buffer } = require('node:buffer');

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

for (const key of buf.keys()) {
  console.log(key);
}
buf.lastIndexOf(value[, byteOffset][, encoding])#

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

import { Buffer } from 'node:buffer';

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

console.log(buf.lastIndexOf('this'));

console.log(buf.lastIndexOf('buffer'));

console.log(buf.lastIndexOf(Buffer.from('buffer')));

console.log(buf.lastIndexOf(97));

console.log(buf.lastIndexOf(Buffer.from('yolo')));

console.log(buf.lastIndexOf('buffer', 5));

console.log(buf.lastIndexOf('buffer', 4));


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

console.log(utf16Buffer.lastIndexOf('\u03a3', undefined, 'utf16le'));

console.log(utf16Buffer.lastIndexOf('\u03a3', -5, 'utf16le'));
const { Buffer } = require('node:buffer');

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

console.log(buf.lastIndexOf('this'));

console.log(buf.lastIndexOf('buffer'));

console.log(buf.lastIndexOf(Buffer.from('buffer')));

console.log(buf.lastIndexOf(97));

console.log(buf.lastIndexOf(Buffer.from('yolo')));

console.log(buf.lastIndexOf('buffer', 5));

console.log(buf.lastIndexOf('buffer', 4));


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

console.log(utf16Buffer.lastIndexOf('\u03a3', undefined, 'utf16le'));

console.log(utf16Buffer.lastIndexOf('\u03a3', -5, 'utf16le'));

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.prototype.lastIndexOf().

import { Buffer } from 'node:buffer';

const b = Buffer.from('abcdef');



console.log(b.lastIndexOf(99.9));
console.log(b.lastIndexOf(256 + 99));



console.log(b.lastIndexOf('b', undefined));
console.log(b.lastIndexOf('b', {}));



console.log(b.lastIndexOf('b', null));
console.log(b.lastIndexOf('b', []));const { Buffer } = require('node:buffer');

const b = Buffer.from('abcdef');



console.log(b.lastIndexOf(99.9));
console.log(b.lastIndexOf(256 + 99));



console.log(b.lastIndexOf('b', undefined));
console.log(b.lastIndexOf('b', {}));



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 number of bytes in buf.

import { Buffer } from 'node:buffer';



const buf = Buffer.alloc(1234);

console.log(buf.length);


buf.write('some string', 0, 'utf8');

console.log(buf.length);
const { Buffer } = require('node:buffer');



const buf = Buffer.alloc(1234);

console.log(buf.length);


buf.write('some string', 0, 'utf8');

console.log(buf.length);
buf.parent#

Deprecated since: v8.0.0

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

buf.readBigInt64BE([offset])#

Added in: v12.0.0, v10.20.0

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

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

buf.readBigInt64LE([offset])#

Added in: v12.0.0, v10.20.0

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

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

buf.readBigUInt64BE([offset])#

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

This function is also available under the readBigUint64BE alias.

import { Buffer } from 'node:buffer';

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

console.log(buf.readBigUInt64BE(0));
const { Buffer } = require('node:buffer');

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

console.log(buf.readBigUInt64BE(0));
buf.readBigUInt64LE([offset])#

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

This function is also available under the readBigUint64LE alias.

import { Buffer } from 'node:buffer';

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

console.log(buf.readBigUInt64LE(0));
const { Buffer } = require('node:buffer');

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

console.log(buf.readBigUInt64LE(0));
buf.readDoubleBE([offset])#

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

import { Buffer } from 'node:buffer';

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

console.log(buf.readDoubleBE(0));
const { Buffer } = require('node:buffer');

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

console.log(buf.readDoubleBE(0));
buf.readDoubleLE([offset])#

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

import { Buffer } from 'node:buffer';

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

console.log(buf.readDoubleLE(0));

console.log(buf.readDoubleLE(1));
const { Buffer } = require('node:buffer');

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

console.log(buf.readDoubleLE(0));

console.log(buf.readDoubleLE(1));
buf.readFloatBE([offset])#

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

import { Buffer } from 'node:buffer';

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

console.log(buf.readFloatBE(0));
const { Buffer } = require('node:buffer');

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

console.log(buf.readFloatBE(0));
buf.readFloatLE([offset])#

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

import { Buffer } from 'node:buffer';

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

console.log(buf.readFloatLE(0));

console.log(buf.readFloatLE(1));
const { Buffer } = require('node:buffer');

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

console.log(buf.readFloatLE(0));

console.log(buf.readFloatLE(1));
buf.readInt8([offset])#

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 'node:buffer';

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

console.log(buf.readInt8(0));

console.log(buf.readInt8(1));

console.log(buf.readInt8(2));
const { Buffer } = require('node:buffer');

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

console.log(buf.readInt8(0));

console.log(buf.readInt8(1));

console.log(buf.readInt8(2));
buf.readInt16BE([offset])#

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 'node:buffer';

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

console.log(buf.readInt16BE(0));
const { Buffer } = require('node:buffer');

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

console.log(buf.readInt16BE(0));
buf.readInt16LE([offset])#

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

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

import { Buffer } from 'node:buffer';

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

console.log(buf.readInt16LE(0));

console.log(buf.readInt16LE(1));
const { Buffer } = require('node:buffer');

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

console.log(buf.readInt16LE(0));

console.log(buf.readInt16LE(1));
buf.readInt32BE([offset])#

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 'node:buffer';

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

console.log(buf.readInt32BE(0));
const { Buffer } = require('node:buffer');

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

console.log(buf.readInt32BE(0));
buf.readInt32LE([offset])#

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

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

import { Buffer } from 'node:buffer';

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

console.log(buf.readInt32LE(0));

console.log(buf.readInt32LE(1));
const { Buffer } = require('node:buffer');

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

console.log(buf.readInt32LE(0));

console.log(buf.readInt32LE(1));
buf.readIntBE(offset, byteLength)#

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

import { Buffer } from 'node:buffer';

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

console.log(buf.readIntBE(0, 6).toString(16));

console.log(buf.readIntBE(1, 6).toString(16));

console.log(buf.readIntBE(1, 0).toString(16));
const { Buffer } = require('node:buffer');

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

console.log(buf.readIntBE(0, 6).toString(16));

console.log(buf.readIntBE(1, 6).toString(16));

console.log(buf.readIntBE(1, 0).toString(16));
buf.readIntLE(offset, byteLength)#

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

import { Buffer } from 'node:buffer';

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

console.log(buf.readIntLE(0, 6).toString(16));
const { Buffer } = require('node:buffer');

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

console.log(buf.readIntLE(0, 6).toString(16));
buf.readUInt8([offset])#

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

This function is also available under the readUint8 alias.

import { Buffer } from 'node:buffer';

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

console.log(buf.readUInt8(0));

console.log(buf.readUInt8(1));

console.log(buf.readUInt8(2));
const { Buffer } = require('node:buffer');

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

console.log(buf.readUInt8(0));

console.log(buf.readUInt8(1));

console.log(buf.readUInt8(2));
buf.readUInt16BE([offset])#

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

This function is also available under the readUint16BE alias.

import { Buffer } from 'node:buffer';

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

console.log(buf.readUInt16BE(0).toString(16));

console.log(buf.readUInt16BE(1).toString(16));
const { Buffer } = require('node:buffer');

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

console.log(buf.readUInt16BE(0).toString(16));

console.log(buf.readUInt16BE(1).toString(16));
buf.readUInt16LE([offset])#

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

This function is also available under the readUint16LE alias.

import { Buffer } from 'node:buffer';

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

console.log(buf.readUInt16LE(0).toString(16));

console.log(buf.readUInt16LE(1).toString(16));

console.log(buf.readUInt16LE(2).toString(16));
const { Buffer } = require('node:buffer');

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

console.log(buf.readUInt16LE(0).toString(16));

console.log(buf.readUInt16LE(1).toString(16));

console.log(buf.readUInt16LE(2).toString(16));
buf.readUInt32BE([offset])#

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

This function is also available under the readUint32BE alias.

import { Buffer } from 'node:buffer';

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

console.log(buf.readUInt32BE(0).toString(16));
const { Buffer } = require('node:buffer');

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

console.log(buf.readUInt32BE(0).toString(16));
buf.readUInt32LE([offset])#

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

This function is also available under the readUint32LE alias.

import { Buffer } from 'node:buffer';

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

console.log(buf.readUInt32LE(0).toString(16));

console.log(buf.readUInt32LE(1).toString(16));
const { Buffer } = require('node:buffer');

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

console.log(buf.readUInt32LE(0).toString(16));

console.log(buf.readUInt32LE(1).toString(16));
buf.readUIntBE(offset, byteLength)#

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

This function is also available under the readUintBE alias.

import { Buffer } from 'node:buffer';

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

console.log(buf.readUIntBE(0, 6).toString(16));

console.log(buf.readUIntBE(1, 6).toString(16));
const { Buffer } = require('node:buffer');

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

console.log(buf.readUIntBE(0, 6).toString(16));

console.log(buf.readUIntBE(1, 6).toString(16));
buf.readUIntLE(offset, byteLength)#

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

This function is also available under the readUintLE alias.

import { Buffer } from 'node:buffer';

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

console.log(buf.readUIntLE(0, 6).toString(16));
const { Buffer } = require('node:buffer');

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

console.log(buf.readUIntLE(0, 6).toString(16));
buf.subarray([start[, end]])#

Added in: v3.0.0

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

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 Buffer because the allocated memory of the two objects overlap.

import { Buffer } from 'node:buffer';




const buf1 = Buffer.allocUnsafe(26);

for (let i = 0; i < 26; i++) {
  
  buf1[i] = i + 97;
}

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

console.log(buf2.toString('ascii', 0, buf2.length));


buf1[0] = 33;

console.log(buf2.toString('ascii', 0, buf2.length));
const { Buffer } = require('node:buffer');




const buf1 = Buffer.allocUnsafe(26);

for (let i = 0; i < 26; i++) {
  
  buf1[i] = i + 97;
}

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

console.log(buf2.toString('ascii', 0, buf2.length));


buf1[0] = 33;

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.

import { Buffer } from 'node:buffer';

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

console.log(buf.subarray(-6, -1).toString());



console.log(buf.subarray(-6, -2).toString());



console.log(buf.subarray(-5, -2).toString());

const { Buffer } = require('node:buffer');

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

console.log(buf.subarray(-6, -1).toString());



console.log(buf.subarray(-6, -2).toString());



console.log(buf.subarray(-5, -2).toString());
buf.slice([start[, end]])#

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

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

import { Buffer } from 'node:buffer';

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

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


console.log(buf.toString());



const notReallyCopiedBuf = buf.slice();
notReallyCopiedBuf[0]++;
console.log(notReallyCopiedBuf.toString());

console.log(buf.toString());
const { Buffer } = require('node:buffer');

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

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


console.log(buf.toString());



const notReallyCopiedBuf = buf.slice();
notReallyCopiedBuf[0]++;
console.log(notReallyCopiedBuf.toString());

console.log(buf.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 ERR_INVALID_BUFFER_SIZE if buf.length is not a multiple of 2.

import { Buffer } from 'node:buffer';

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

console.log(buf1);


buf1.swap16();

console.log(buf1);


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

buf2.swap16();
const { Buffer } = require('node:buffer');

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

console.log(buf1);


buf1.swap16();

console.log(buf1);


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

buf2.swap16();

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 'node:buffer';

const buf = Buffer.from('This is little-endian UTF-16', 'utf16le');
buf.swap16(); const { Buffer } = require('node:buffer');

const buf = Buffer.from('This is little-endian UTF-16', 'utf16le');
buf.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 ERR_INVALID_BUFFER_SIZE if buf.length is not a multiple of 4.

import { Buffer } from 'node:buffer';

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

console.log(buf1);


buf1.swap32();

console.log(buf1);


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

buf2.swap32();
const { Buffer } = require('node:buffer');

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

console.log(buf1);


buf1.swap32();

console.log(buf1);


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

buf2.swap32();
buf.swap64()#

Added in: v6.3.0

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 'node:buffer';

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

console.log(buf1);


buf1.swap64();

console.log(buf1);


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

buf2.swap64();
const { Buffer } = require('node:buffer');

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

console.log(buf1);


buf1.swap64();

console.log(buf1);


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

buf2.swap64();
buf.toJSON()#

Added in: v0.9.2

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 'node:buffer';

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

console.log(json);


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

console.log(copy);
const { Buffer } = require('node:buffer');

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

console.log(json);


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

console.log(copy);
buf.toString([encoding[, start[, end]]])#

Added in: v0.1.90

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

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

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

import { Buffer } from 'node:buffer';

const buf1 = Buffer.allocUnsafe(26);

for (let i = 0; i < 26; i++) {
  
  buf1[i] = i + 97;
}

console.log(buf1.toString('utf8'));

console.log(buf1.toString('utf8', 0, 5));


const buf2 = Buffer.from('tést');

console.log(buf2.toString('hex'));

console.log(buf2.toString('utf8', 0, 3));

console.log(buf2.toString(undefined, 0, 3));
const { Buffer } = require('node:buffer');

const buf1 = Buffer.allocUnsafe(26);

for (let i = 0; i < 26; i++) {
  
  buf1[i] = i + 97;
}

console.log(buf1.toString('utf8'));

console.log(buf1.toString('utf8', 0, 5));


const buf2 = Buffer.from('tést');

console.log(buf2.toString('hex'));

console.log(buf2.toString('utf8', 0, 3));

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.

import { Buffer } from 'node:buffer';

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

for (const value of buf.values()) {
  console.log(value);
}








for (const value of buf) {
  console.log(value);
}






const { Buffer } = require('node:buffer');

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

for (const value of buf.values()) {
  console.log(value);
}








for (const value of buf) {
  console.log(value);
}
buf.write(string[, offset[, length]][, encoding])#

Added in: v0.1.90

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

import { Buffer } from 'node:buffer';

const buf = Buffer.alloc(256);

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

console.log(`${len} bytes: ${buf.toString('utf8', 0, len)}`);


const buffer = Buffer.alloc(10);

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

console.log(`${length} bytes: ${buffer.toString('utf8', 8, 10)}`);
const { Buffer } = require('node:buffer');

const buf = Buffer.alloc(256);

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

console.log(`${len} bytes: ${buf.toString('utf8', 0, len)}`);


const buffer = Buffer.alloc(10);

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

console.log(`${length} bytes: ${buffer.toString('utf8', 8, 10)}`);
buf.writeBigInt64BE(value[, offset])#

Added in: v12.0.0, v10.20.0

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 'node:buffer';

const buf = Buffer.allocUnsafe(8);

buf.writeBigInt64BE(0x0102030405060708n, 0);

console.log(buf);
const { Buffer } = require('node:buffer');

const buf = Buffer.allocUnsafe(8);

buf.writeBigInt64BE(0x0102030405060708n, 0);

console.log(buf);
buf.writeBigInt64LE(value[, offset])#

Added in: v12.0.0, v10.20.0

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 'node:buffer';

const buf = Buffer.allocUnsafe(8);

buf.writeBigInt64LE(0x0102030405060708n, 0);

console.log(buf);
const { Buffer } = require('node:buffer');

const buf = Buffer.allocUnsafe(8);

buf.writeBigInt64LE(0x0102030405060708n, 0);

console.log(buf);
buf.writeBigUInt64BE(value[, offset])#

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

This function is also available under the writeBigUint64BE alias.

import { Buffer } from 'node:buffer';

const buf = Buffer.allocUnsafe(8);

buf.writeBigUInt64BE(0xdecafafecacefaden, 0);

console.log(buf);
const { Buffer } = require('node:buffer');

const buf = Buffer.allocUnsafe(8);

buf.writeBigUInt64BE(0xdecafafecacefaden, 0);

console.log(buf);
buf.writeBigUInt64LE(value[, offset])#

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

import { Buffer } from 'node:buffer';

const buf = Buffer.allocUnsafe(8);

buf.writeBigUInt64LE(0xdecafafecacefaden, 0);

console.log(buf);
const { Buffer } = require('node:buffer');

const buf = Buffer.allocUnsafe(8);

buf.writeBigUInt64LE(0xdecafafecacefaden, 0);

console.log(buf);

This function is also available under the writeBigUint64LE alias.

buf.writeDoubleBE(value[, offset])#

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

import { Buffer } from 'node:buffer';

const buf = Buffer.allocUnsafe(8);

buf.writeDoubleBE(123.456, 0);

console.log(buf);
const { Buffer } = require('node:buffer');

const buf = Buffer.allocUnsafe(8);

buf.writeDoubleBE(123.456, 0);

console.log(buf);
buf.writeDoubleLE(value[, offset])#

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

import { Buffer } from 'node:buffer';

const buf = Buffer.allocUnsafe(8);

buf.writeDoubleLE(123.456, 0);

console.log(buf);
const { Buffer } = require('node:buffer');

const buf = Buffer.allocUnsafe(8);

buf.writeDoubleLE(123.456, 0);

console.log(buf);
buf.writeFloatBE(value[, offset])#

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 'node:buffer';

const buf = Buffer.allocUnsafe(4);

buf.writeFloatBE(0xcafebabe, 0);

console.log(buf);
const { Buffer } = require('node:buffer');

const buf = Buffer.allocUnsafe(4);

buf.writeFloatBE(0xcafebabe, 0);

console.log(buf);
buf.writeFloatLE(value[, offset])#

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 'node:buffer';

const buf = Buffer.allocUnsafe(4);

buf.writeFloatLE(0xcafebabe, 0);

console.log(buf);
const { Buffer } = require('node:buffer');

const buf = Buffer.allocUnsafe(4);

buf.writeFloatLE(0xcafebabe, 0);

console.log(buf);
buf.writeInt8(value[, offset])#

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 'node:buffer';

const buf = Buffer.allocUnsafe(2);

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

console.log(buf);
const { Buffer } = require('node:buffer');

const buf = Buffer.allocUnsafe(2);

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

console.log(buf);
buf.writeInt16BE(value[, offset])#

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

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

import { Buffer } from 'node:buffer';

const buf = Buffer.allocUnsafe(2);

buf.writeInt16BE(0x0102, 0);

console.log(buf);
const { Buffer } = require('node:buffer');

const buf = Buffer.allocUnsafe(2);

buf.writeInt16BE(0x0102, 0);

console.log(buf);
buf.writeInt16LE(value[, offset])#

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

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

import { Buffer } from 'node:buffer';

const buf = Buffer.allocUnsafe(2);

buf.writeInt16LE(0x0304, 0);

console.log(buf);
const { Buffer } = require('node:buffer');

const buf = Buffer.allocUnsafe(2);

buf.writeInt16LE(0x0304, 0);

console.log(buf);
buf.writeInt32BE(value[, offset])#

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

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

import { Buffer } from 'node:buffer';

const buf = Buffer.allocUnsafe(4);

buf.writeInt32BE(0x01020304, 0);

console.log(buf);
const { Buffer } = require('node:buffer');

const buf = Buffer.allocUnsafe(4);

buf.writeInt32BE(0x01020304, 0);

console.log(buf);
buf.writeInt32LE(value[, offset])#

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

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

import { Buffer } from 'node:buffer';

const buf = Buffer.allocUnsafe(4);

buf.writeInt32LE(0x05060708, 0);

console.log(buf);
const { Buffer } = require('node:buffer');

const buf = Buffer.allocUnsafe(4);

buf.writeInt32LE(0x05060708, 0);

console.log(buf);
buf.writeIntBE(value, offset, byteLength)#

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

import { Buffer } from 'node:buffer';

const buf = Buffer.allocUnsafe(6);

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

console.log(buf);
const { Buffer } = require('node:buffer');

const buf = Buffer.allocUnsafe(6);

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

console.log(buf);
buf.writeIntLE(value, offset, byteLength)#

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

import { Buffer } from 'node:buffer';

const buf = Buffer.allocUnsafe(6);

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

console.log(buf);
const { Buffer } = require('node:buffer');

const buf = Buffer.allocUnsafe(6);

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

console.log(buf);
buf.writeUInt8(value[, offset])#

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 'node: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);
const { Buffer } = require('node: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);
buf.writeUInt16BE(value[, offset])#

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

This function is also available under the writeUint16BE alias.

import { Buffer } from 'node:buffer';

const buf = Buffer.allocUnsafe(4);

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

console.log(buf);
const { Buffer } = require('node:buffer');

const buf = Buffer.allocUnsafe(4);

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

console.log(buf);
buf.writeUInt16LE(value[, offset])#

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

This function is also available under the writeUint16LE alias.

import { Buffer } from 'node:buffer';

const buf = Buffer.allocUnsafe(4);

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

console.log(buf);
const { Buffer } = require('node:buffer');

const buf = Buffer.allocUnsafe(4);

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

console.log(buf);
buf.writeUInt32BE(value[, offset])#

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

This function is also available under the writeUint32BE alias.

import { Buffer } from 'node:buffer';

const buf = Buffer.allocUnsafe(4);

buf.writeUInt32BE(0xfeedface, 0);

console.log(buf);
const { Buffer } = require('node:buffer');

const buf = Buffer.allocUnsafe(4);

buf.writeUInt32BE(0xfeedface, 0);

console.log(buf);
buf.writeUInt32LE(value[, offset])#

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

This function is also available under the writeUint32LE alias.

import { Buffer } from 'node:buffer';

const buf = Buffer.allocUnsafe(4);

buf.writeUInt32LE(0xfeedface, 0);

console.log(buf);
const { Buffer } = require('node:buffer');

const buf = Buffer.allocUnsafe(4);

buf.writeUInt32LE(0xfeedface, 0);

console.log(buf);
buf.writeUIntBE(value, offset, byteLength)#

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

This function is also available under the writeUintBE alias.

import { Buffer } from 'node:buffer';

const buf = Buffer.allocUnsafe(6);

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

console.log(buf);
const { Buffer } = require('node:buffer');

const buf = Buffer.allocUnsafe(6);

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

console.log(buf);
buf.writeUIntLE(value, offset, byteLength)#

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

This function is also available under the writeUintLE alias.

import { Buffer } from 'node:buffer';

const buf = Buffer.allocUnsafe(6);

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

console.log(buf);
const { Buffer } = require('node:buffer');

const buf = Buffer.allocUnsafe(6);

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

console.log(buf);
Class: File#

A <File> provides information about files.

new buffer.File(sources, fileName[, options])#

Added in: v19.2.0, v18.13.0

file.name#

Added in: v19.2.0, v18.13.0

The name of the File.

file.lastModified#

Added in: v19.2.0, v18.13.0

The last modified date of the File.

node:buffer module APIs#

While, the Buffer object is available as a global, there are additional Buffer-related APIs that are available only via the node:buffer module accessed using require('node:buffer').

buffer.atob(data)#

Added in: v15.13.0, v14.17.0

Stability: 3

- Legacy. Use

Buffer.from(data, 'base64')

instead.

Decodes a string of Base64-encoded data into bytes, and encodes those bytes into a string using Latin-1 (ISO-8859-1).

The data may be any JavaScript-value that can be coerced into a string.

This function is only provided for compatibility with legacy web platform APIs and should never be used in new code, because they use strings to represent binary data and predate the introduction of typed arrays in JavaScript. For code running using Node.js APIs, converting between base64-encoded strings and binary data should be performed using Buffer.from(str, 'base64') and buf.toString('base64').

buffer.btoa(data)#

Added in: v15.13.0, v14.17.0

Decodes a string into bytes using Latin-1 (ISO-8859), and encodes those bytes into a string using Base64.

The data may be any JavaScript-value that can be coerced into a string.

This function is only provided for compatibility with legacy web platform APIs and should never be used in new code, because they use strings to represent binary data and predate the introduction of typed arrays in JavaScript. For code running using Node.js APIs, converting between base64-encoded strings and binary data should be performed using Buffer.from(str, 'base64') and buf.toString('base64').

buffer.isAscii(input)#

Added in: v19.6.0, v18.15.0

This function returns true if input contains only valid ASCII-encoded data, including the case in which input is empty.

Throws if the input is a detached array buffer.

buffer.isUtf8(input)#

Added in: v19.4.0, v18.14.0

This function returns true if input contains only valid UTF-8-encoded data, including the case in which input is empty.

Throws if the input is a detached array buffer.

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.

buffer.resolveObjectURL(id)#

Resolves a 'blob:nodedata:...' an associated <Blob> object registered using a prior call to URL.createObjectURL().

buffer.transcode(source, fromEnc, toEnc)#

Re-encodes the given Buffer or Uint8Array instance from one character encoding to another. Returns a new Buffer instance.

Throws if the fromEnc or toEnc specify invalid character encodings or if conversion from fromEnc to toEnc is not permitted.

Encodings supported by buffer.transcode() are: 'ascii', 'utf8', 'utf16le', 'ucs2', 'latin1', and 'binary'.

The transcoding process will use substitution characters if a given byte sequence cannot be adequately represented in the target encoding. For instance:

import { Buffer, transcode } from 'node:buffer';

const newBuf = transcode(Buffer.from('€'), 'utf8', 'ascii');
console.log(newBuf.toString('ascii'));
const { Buffer, transcode } = require('node:buffer');

const newBuf = transcode(Buffer.from('€'), 'utf8', 'ascii');
console.log(newBuf.toString('ascii'));

Because the Euro (€) sign is not representable in US-ASCII, it is replaced with ? in the transcoded Buffer.

Class: SlowBuffer#

Deprecated since: v6.0.0

See Buffer.allocUnsafeSlow(). This was never a class in the sense that the constructor always returned a Buffer instance, rather than a SlowBuffer instance.

Buffer constants#

Added in: v8.2.0

buffer.constants.MAX_LENGTH#

On 32-bit architectures, this value currently is 230 - 1 (about 1 GiB).

On 64-bit architectures, this value currently is 253 - 1 (about 8 PiB).

It reflects v8::TypedArray::kMaxLength under the hood.

This value is also available as buffer.kMaxLength.

buffer.constants.MAX_STRING_LENGTH#

Added in: v8.2.0

Represents the largest length that a string primitive can have, counted in UTF-16 code units.

This value may depend on the JS engine that is being used.

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

In versions of Node.js prior to 6.0.0, Buffer instances were created using the Buffer constructor function, which allocates the returned Buffer differently based on what arguments are provided:

Because the behavior of new Buffer() is different depending on the type of the first argument, security and reliability issues can be inadvertently introduced into applications when argument validation or Buffer initialization is not performed.

For example, if an attacker can cause an application to receive a number where a string is expected, the application may call new Buffer(100) instead of new Buffer("100"), leading it to allocate a 100 byte buffer instead of allocating a 3 byte buffer with content "100". This is commonly possible using JSON API calls. Since JSON distinguishes between numeric and string types, it allows injection of numbers where a naively written application that does not validate its input sufficiently might expect to always receive a string. Before Node.js 8.0.0, the 100 byte buffer might contain arbitrary pre-existing in-memory data, so may be used to expose in-memory secrets to a remote attacker. Since Node.js 8.0.0, exposure of memory cannot occur because the data is zero-filled. However, other attacks are still possible, such as causing very large buffers to be allocated by the server, leading to performance degradation or crashing on memory exhaustion.

To make the creation of Buffer instances more reliable and less error-prone, the various forms of the new Buffer() constructor have been deprecated and replaced by separate Buffer.from(), Buffer.alloc(), and Buffer.allocUnsafe() methods.

Developers should migrate all existing uses of the new Buffer() constructors to one of these new APIs.

Buffer instances returned by Buffer.allocUnsafe(), Buffer.from(string), Buffer.concat() and Buffer.from(array) may be allocated off a shared internal memory pool if size is less than or equal to half Buffer.poolSize. Instances returned by Buffer.allocUnsafeSlow() never use the shared internal memory pool.

The --zero-fill-buffers command-line option#

Added in: v5.10.0

Node.js can be started using the --zero-fill-buffers command-line option to cause all newly-allocated Buffer instances to be zero-filled upon creation by default. Without the option, buffers created with Buffer.allocUnsafe(), Buffer.allocUnsafeSlow(), and new SlowBuffer(size) are not zero-filled. Use of this flag can have a measurable negative impact on performance. Use the --zero-fill-buffers option only when necessary to enforce that newly allocated Buffer instances cannot contain old data that is potentially sensitive.

$ node --zero-fill-buffers
> Buffer.allocUnsafe(5);
<Buffer 00 00 00 00 00>
What makes Buffer.allocUnsafe() and Buffer.allocUnsafeSlow() "unsafe"?#

When calling Buffer.allocUnsafe() and Buffer.allocUnsafeSlow(), the segment of allocated memory is uninitialized (it is not zeroed-out). While this design makes the allocation of memory quite fast, the allocated segment of memory might contain old data that is potentially sensitive. Using a Buffer created by Buffer.allocUnsafe() without completely overwriting the memory can allow this old data to be leaked when the Buffer memory is read.

While there are clear performance advantages to using Buffer.allocUnsafe(), extra care must be taken in order to avoid introducing security vulnerabilities into an application.

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