Gecko [ thecigaretteboxes.com ]

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Code Editor : buffer.md

# Buffer

> Stability: 2 - Stable

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

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

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

```mjs
import { Buffer } from 'node: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');
```

```cjs
const { Buffer } = require('node: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 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 Latin-1 bytes [0x74, 0xe9, 0x73, 0x74].
const buf7 = Buffer.from('tést', 'latin1');
```

## Buffers and character encodings

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

```mjs
import { Buffer } from 'node:buffer';

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

console.log(buf.toString('hex'));
// Prints: 68656c6c6f20776f726c64
console.log(buf.toString('base64'));
// Prints: aGVsbG8gd29ybGQ=

console.log(Buffer.from('fhqwhgads', 'utf8'));
// Prints: <Buffer 66 68 71 77 68 67 61 64 73>
console.log(Buffer.from('fhqwhgads', 'utf16le'));
// Prints: <Buffer 66 00 68 00 71 00 77 00 68 00 67 00 61 00 64 00 73 00>
```

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

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

console.log(buf.toString('hex'));
// Prints: 68656c6c6f20776f726c64
console.log(buf.toString('base64'));
// Prints: aGVsbG8gd29ybGQ=

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:

* `'utf8'` (alias: `'utf-8'`): Multi-byte encoded Unicode characters. Many web
  pages and other document formats use [UTF-8][]. This is the default character
  encoding. When decoding a `Buffer` into a string that does not exclusively
  contain valid UTF-8 data, the Unicode replacement character `U+FFFD` � will be
  used to represent those errors.

* `'utf16le'` (alias: `'utf-16le'`): Multi-byte encoded Unicode characters.
  Unlike `'utf8'`, each character in the string will be encoded using either 2
  or 4 bytes. Node.js only supports the [little-endian][endianness] variant of
  [UTF-16][].

* `'latin1'`: Latin-1 stands for [ISO-8859-1][]. This character encoding only
  supports the Unicode characters from `U+0000` to `U+00FF`. Each character is
  encoded using a single byte. Characters that do not fit into that range are
  truncated and will be mapped to characters in that range.

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

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

* `'base64'`: [Base64][] encoding. When creating a `Buffer` from a string,
  this encoding will also correctly accept "URL and Filename Safe Alphabet" as
  specified in [RFC 4648, Section 5][]. Whitespace characters such as spaces,
  tabs, and new lines contained within the base64-encoded string are ignored.

* `'base64url'`: [base64url][] encoding as specified in
  [RFC 4648, Section 5][]. When creating a `Buffer` from a string, this
  encoding will also correctly accept regular base64-encoded strings. When
  encoding a `Buffer` to a string, this encoding will omit padding.

* `'hex'`: Encode each byte as two hexadecimal characters. Data truncation
  may occur when decoding strings that do not exclusively consist of an even
  number of hexadecimal characters. See below for an example.

The following legacy character encodings are also supported:

* `'ascii'`: For 7-bit [ASCII][] data only. When encoding a string into a
  `Buffer`, this is equivalent to using `'latin1'`. When decoding a `Buffer`
  into a string, using this encoding will additionally unset the highest bit of
  each byte before decoding as `'latin1'`.
  Generally, there should be no reason to use this encoding, as `'utf8'`
  (or, if the data is known to always be ASCII-only, `'latin1'`) will be a
  better choice when encoding or decoding ASCII-only text. It is only provided
  for legacy compatibility.

* `'binary'`: Alias for `'latin1'`.
  The name of this encoding can be very misleading, as all of the
  encodings listed here convert between strings and binary data. For converting
  between strings and `Buffer`s, typically `'utf8'` is the right choice.

* `'ucs2'`, `'ucs-2'`: Aliases of `'utf16le'`. UCS-2 used to refer to a variant
  of UTF-16 that did not support characters that had code points larger than
  U+FFFF. In Node.js, these code points are always supported.

```mjs
import { Buffer } from 'node:buffer';

Buffer.from('1ag123', 'hex');
// Prints <Buffer 1a>, data truncated when first non-hexadecimal value
// ('g') encountered.

Buffer.from('1a7', 'hex');
// Prints <Buffer 1a>, data truncated when data ends in single digit ('7').

Buffer.from('1634', 'hex');
// Prints <Buffer 16 34>, all data represented.
```

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

Buffer.from('1ag123', 'hex');
// Prints <Buffer 1a>, data truncated when first non-hexadecimal value
// ('g') encountered.

Buffer.from('1a7', 'hex');
// Prints <Buffer 1a>, data truncated when data ends in single digit ('7').

Buffer.from('1634', 'hex');
// Prints <Buffer 16 34>, all data represented.
```

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

## Buffers and TypedArrays

`Buffer` instances are also JavaScript [`Uint8Array`][] and [`TypedArray`][]
instances. All [`TypedArray`][] methods are available on `Buffer`s. There are,
however, subtle incompatibilities between the `Buffer` API and the
[`TypedArray`][] API.

In particular:

* While [`TypedArray.prototype.slice()`][] creates a copy of part of the `TypedArray`,
  [`Buffer.prototype.slice()`][`buf.slice()`] creates a view over the existing `Buffer`
  without copying. This behavior can be surprising, and only exists for legacy
  compatibility. [`TypedArray.prototype.subarray()`][] can be used to achieve
  the behavior of [`Buffer.prototype.slice()`][`buf.slice()`] on both `Buffer`s
  and other `TypedArray`s and should be preferred.
* [`buf.toString()`][] is incompatible with its `TypedArray` equivalent.
* A number of methods, e.g. [`buf.indexOf()`][], support additional arguments.

There are two ways to create new [`TypedArray`][] instances from a `Buffer`:

* Passing a `Buffer` to a [`TypedArray`][] constructor will copy the `Buffer`s
  contents, interpreted as an array of integers, and not as a byte sequence
  of the target type.

```mjs
import { Buffer } from 'node:buffer';

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

console.log(uint32array);

// Prints: Uint32Array(4) [ 1, 2, 3, 4 ]
```

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

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

console.log(uint32array);

// Prints: Uint32Array(4) [ 1, 2, 3, 4 ]
```

* Passing the `Buffer`s underlying [`ArrayBuffer`][] will create a
  [`TypedArray`][] that shares its memory with the `Buffer`.

```mjs
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);

// Prints: Uint16Array(5) [ 104, 101, 108, 108, 111 ]
```

```cjs
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);

// Prints: Uint16Array(5) [ 104, 101, 108, 108, 111 ]
```

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

```mjs
import { Buffer } from 'node:buffer';

const arr = new Uint16Array(2);

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

// Copies the contents of `arr`.
const buf1 = Buffer.from(arr);

// Shares memory with `arr`.
const buf2 = Buffer.from(arr.buffer);

console.log(buf1);
// Prints: <Buffer 88 a0>
console.log(buf2);
// Prints: <Buffer 88 13 a0 0f>

arr[1] = 6000;

console.log(buf1);
// Prints: <Buffer 88 a0>
console.log(buf2);
// Prints: <Buffer 88 13 70 17>
```

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

const arr = new Uint16Array(2);

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

// Copies the contents of `arr`.
const buf1 = Buffer.from(arr);

// Shares memory with `arr`.
const buf2 = Buffer.from(arr.buffer);

console.log(buf1);
// Prints: <Buffer 88 a0>
console.log(buf2);
// Prints: <Buffer 88 13 a0 0f>

arr[1] = 6000;

console.log(buf1);
// Prints: <Buffer 88 a0>
console.log(buf2);
// Prints: <Buffer 88 13 70 17>
```

When creating a `Buffer` using a [`TypedArray`][]'s `.buffer`, it is
possible to use only a portion of the underlying [`ArrayBuffer`][] by passing in
`byteOffset` and `length` parameters.

```mjs
import { Buffer } from 'node:buffer';

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

console.log(buf.length);
// Prints: 16
```

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

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

console.log(buf.length);
// Prints: 16
```

The `Buffer.from()` and [`TypedArray.from()`][] have different signatures and
implementations. Specifically, the [`TypedArray`][] variants accept a second
argument that is a mapping function that is invoked on every element of the
typed array:

* `TypedArray.from(source[, mapFn[, thisArg]])`

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

* [`Buffer.from(array)`][]
* [`Buffer.from(buffer)`][]
* [`Buffer.from(arrayBuffer[, byteOffset[, length]])`][`Buffer.from(arrayBuf)`]
* [`Buffer.from(string[, encoding])`][`Buffer.from(string)`]

## Buffers and iteration

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

```mjs
import { Buffer } from 'node:buffer';

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

for (const b of buf) {
  console.log(b);
}
// Prints:
//   1
//   2
//   3
```

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

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

for (const b of buf) {
  console.log(b);
}
// Prints:
//   1
//   2
//   3
```

Additionally, the [`buf.values()`][], [`buf.keys()`][], and
[`buf.entries()`][] methods can be used to create iterators.

## Class: `Blob`

A [`Blob`][] encapsulates immutable, raw data that can be safely shared across
multiple worker threads.

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

* `sources` {string\[]|ArrayBuffer\[]|TypedArray\[]|DataView\[]|Blob\[]} An
  array of string, {ArrayBuffer}, {TypedArray}, {DataView}, or {Blob} objects,
  or any mix of such objects, that will be stored within the `Blob`.
* `options` {Object}
  * `endings` {string} One of either `'transparent'` or `'native'`. When set
    to `'native'`, line endings in string source parts will be converted to
    the platform native line-ending as specified by `require('node:os').EOL`.
  * `type` {string} The Blob content-type. The intent is for `type` to convey
    the MIME media type of the data, however no validation of the type format
    is performed.

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()`

* Returns: {Promise}

Returns a promise that fulfills with an {ArrayBuffer} containing a copy of
the `Blob` data.

### `blob.size`

The total size of the `Blob` in bytes.

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

* `start` {number} The starting index.
* `end` {number} The ending index.
* `type` {string} The content-type for the new `Blob`

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

### `blob.stream()`

* Returns: {ReadableStream}

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

### `blob.text()`

* Returns: {Promise}

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

### `blob.type`

* Type: {string}

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.

```mjs
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);

// The Blob is still usable after posting.
blob.text().then(console.log);
```

```cjs
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);

// The Blob is still usable after posting.
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]])`

* `size` {integer} The desired length of the new `Buffer`.
* `fill` {string|Buffer|Uint8Array|integer} A value to pre-fill the new `Buffer`
  with. **Default:** `0`.
* `encoding` {string} If `fill` is a string, this is its encoding.
  **Default:** `'utf8'`.

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

```mjs
import { Buffer } from 'node:buffer';

const buf = Buffer.alloc(5);

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

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

const buf = Buffer.alloc(5);

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

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

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

```mjs
import { Buffer } from 'node:buffer';

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

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

```cjs
const { Buffer } = require('node: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)`][`buf.fill()`].

```mjs
import { Buffer } from 'node:buffer';

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

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

```cjs
const { Buffer } = require('node: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 `Buffer`s.

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

### Static method: `Buffer.allocUnsafe(size)`

* `size` {integer} The desired length of the new `Buffer`.

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.

```mjs
import { Buffer } from 'node: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>
```

```cjs
const { Buffer } = require('node: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 new
`Buffer` instances created using [`Buffer.allocUnsafe()`][], [`Buffer.from(array)`][],
and [`Buffer.concat()`][] only when `size` is less than or equal to
`Buffer.poolSize >> 1` (floor of [`Buffer.poolSize`][] divided by two).

Use of this pre-allocated internal memory pool is a key difference between
calling `Buffer.alloc(size, fill)` vs. `Buffer.allocUnsafe(size).fill(fill)`.
Specifically, `Buffer.alloc(size, fill)` will _never_ use the internal `Buffer`
pool, while `Buffer.allocUnsafe(size).fill(fill)` _will_ use the internal
`Buffer` pool if `size` is less than or equal to half [`Buffer.poolSize`][]. The
difference is subtle but can be important when an application requires the
additional performance that [`Buffer.allocUnsafe()`][] provides.

### Static method: `Buffer.allocUnsafeSlow(size)`

* `size` {integer} The desired length of the new `Buffer`.

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)`][`buf.fill()`] to initialize
such `Buffer` instances with zeroes.

When using [`Buffer.allocUnsafe()`][] to allocate new `Buffer` instances,
allocations under 4 KiB 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.

```mjs
import { Buffer } from 'node: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);
  }
});
```

```cjs
const { Buffer } = require('node: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.

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

* `string` {string|Buffer|TypedArray|DataView|ArrayBuffer|SharedArrayBuffer} A
  value to calculate the length of.
* `encoding` {string} If `string` is a string, this is its encoding.
  **Default:** `'utf8'`.
* Returns: {integer} The number of bytes contained within `string`.

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

For `'base64'`, `'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.

```mjs
import { Buffer } from 'node: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
```

```cjs
const { Buffer } = require('node: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`][]/[`ArrayBuffer`][]/
[`SharedArrayBuffer`][], the byte length as reported by `.byteLength`
is returned.

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

* `buf1` {Buffer|Uint8Array}
* `buf2` {Buffer|Uint8Array}
* Returns: {integer} Either `-1`, `0`, or `1`, depending on the result of the
  comparison. See [`buf.compare()`][] for details.

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

```mjs
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));
// Prints: [ <Buffer 30 31 32 33>, <Buffer 31 32 33 34> ]
// (This result is equal to: [buf2, buf1].)
```

```cjs
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));
// Prints: [ <Buffer 30 31 32 33>, <Buffer 31 32 33 34> ]
// (This result is equal to: [buf2, buf1].)
```

### Static method: `Buffer.concat(list[, totalLength])`

* `list` {Buffer\[] | Uint8Array\[]} List of `Buffer` or [`Uint8Array`][]
  instances to concatenate.
* `totalLength` {integer} Total length of the `Buffer` instances in `list`
  when concatenated.
* Returns: {Buffer}

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

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

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

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

```mjs
import { Buffer } from 'node: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
```

```cjs
const { Buffer } = require('node: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.

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

* `view` {TypedArray} The {TypedArray} to copy.
* `offset` {integer} The starting offset within `view`. **Default:**: `0`.
* `length` {integer} The number of elements from `view` to copy.
  **Default:** `view.length - offset`.

Copies the underlying memory of `view` into a new `Buffer`.

```js
const u16 = new Uint16Array([0, 0xffff]);
const buf = Buffer.copyBytesFrom(u16, 1, 1);
u16[1] = 0;
console.log(buf.length); // 2
console.log(buf[0]); // 255
console.log(buf[1]); // 255
```

### Static method: `Buffer.from(array)`

* `array` {integer\[]}

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

```mjs
import { Buffer } from 'node:buffer';

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

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

// Creates a new Buffer containing the UTF-8 bytes of the string '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]])`

* `arrayBuffer` {ArrayBuffer|SharedArrayBuffer} An [`ArrayBuffer`][],
  [`SharedArrayBuffer`][], for example the `.buffer` property of a
  [`TypedArray`][].
* `byteOffset` {integer} Index of first byte to expose. **Default:** `0`.
* `length` {integer} Number of bytes to expose.
  **Default:** `arrayBuffer.byteLength - byteOffset`.

This creates a view of the [`ArrayBuffer`][] without copying the underlying
memory. For example, when passed a reference to the `.buffer` property of a
[`TypedArray`][] instance, the newly created `Buffer` will share the same
allocated memory as the [`TypedArray`][]'s underlying `ArrayBuffer`.

```mjs
import { Buffer } from 'node:buffer';

const arr = new Uint16Array(2);

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

// Shares memory with `arr`.
const buf = Buffer.from(arr.buffer);

console.log(buf);
// Prints: <Buffer 88 13 a0 0f>

// Changing the original Uint16Array changes the Buffer also.
arr[1] = 6000;

console.log(buf);
// Prints: <Buffer 88 13 70 17>
```

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

const arr = new Uint16Array(2);

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

// Shares memory with `arr`.
const buf = Buffer.from(arr.buffer);

console.log(buf);
// Prints: <Buffer 88 13 a0 0f>

// Changing the original Uint16Array changes the Buffer also.
arr[1] = 6000;

console.log(buf);
// Prints: <Buffer 88 13 70 17>
```

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

```mjs
import { Buffer } from 'node:buffer';

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

console.log(buf.length);
// Prints: 2
```

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

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

console.log(buf.length);
// Prints: 2
```

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

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`:

```mjs
import { Buffer } from 'node:buffer';

const arrA = Uint8Array.from([0x63, 0x64, 0x65, 0x66]); // 4 elements
const arrB = new Uint8Array(arrA.buffer, 1, 2); // 2 elements
console.log(arrA.buffer === arrB.buffer); // true

const buf = Buffer.from(arrB.buffer);
console.log(buf);
// Prints: <Buffer 63 64 65 66>
```

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

const arrA = Uint8Array.from([0x63, 0x64, 0x65, 0x66]); // 4 elements
const arrB = new Uint8Array(arrA.buffer, 1, 2); // 2 elements
console.log(arrA.buffer === arrB.buffer); // true

const buf = Buffer.from(arrB.buffer);
console.log(buf);
// Prints: <Buffer 63 64 65 66>
```

### Static method: `Buffer.from(buffer)`

* `buffer` {Buffer|Uint8Array} An existing `Buffer` or [`Uint8Array`][] from
  which to copy data.

Copies the passed `buffer` data onto a new `Buffer` instance.

```mjs
import { Buffer } from 'node:buffer';

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

buf1[0] = 0x61;

console.log(buf1.toString());
// Prints: auffer
console.log(buf2.toString());
// Prints: buffer
```

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

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

buf1[0] = 0x61;

console.log(buf1.toString());
// Prints: auffer
console.log(buf2.toString());
// Prints: buffer
```

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

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

* `object` {Object} An object supporting `Symbol.toPrimitive` or `valueOf()`.
* `offsetOrEncoding` {integer|string} A byte-offset or encoding.
* `length` {integer} A length.

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

```mjs
import { Buffer } from 'node:buffer';

const buf = Buffer.from(new String('this is a test'));
// Prints: <Buffer 74 68 69 73 20 69 73 20 61 20 74 65 73 74>
```

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

const buf = Buffer.from(new String('this is a test'));
// Prints: <Buffer 74 68 69 73 20 69 73 20 61 20 74 65 73 74>
```

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

```mjs
import { Buffer } from 'node:buffer';

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

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

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

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

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

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

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

* `string` {string} A string to encode.
* `encoding` {string} The encoding of `string`. **Default:** `'utf8'`.

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

```mjs
import { Buffer } from 'node:buffer';

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

console.log(buf1.toString());
// Prints: this is a tést
console.log(buf2.toString());
// Prints: this is a tést
console.log(buf1.toString('latin1'));
// Prints: this is a tÃ©st
```

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

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

console.log(buf1.toString());
// Prints: this is a tést
console.log(buf2.toString());
// Prints: this is a tést
console.log(buf1.toString('latin1'));
// Prints: this is a tÃ©st
```

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

### Static method: `Buffer.isBuffer(obj)`

* `obj` {Object}
* Returns: {boolean}

Returns `true` if `obj` is a `Buffer`, `false` otherwise.

```mjs
import { Buffer } from 'node: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
```

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

### Static method: `Buffer.isEncoding(encoding)`

* `encoding` {string} A character encoding name to check.
* Returns: {boolean}

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

```mjs
import { Buffer } from 'node: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
```

```cjs
const { Buffer } = require('node: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
```

### Class property: `Buffer.poolSize`

* {integer} **Default:** `8192`

This is the size (in bytes) of pre-allocated internal `Buffer` instances used
for pooling. This value may be modified.

### `buf[index]`

* `index` {integer}

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

This operator is inherited from `Uint8Array`, so its behavior on out-of-bounds
access is the same as `Uint8Array`. In other words, `buf[index]` returns
`undefined` when `index` is negative or greater or equal to `buf.length`, and
`buf[index] = value` does not modify the buffer if `index` is negative or
`>= buf.length`.

```mjs
import { Buffer } from 'node:buffer';

// Copy an ASCII string into a `Buffer` one byte at a time.
// (This only works for ASCII-only strings. In general, one should use
// `Buffer.from()` to perform this conversion.)

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

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

console.log(buf.toString('utf8'));
// Prints: Node.js
```

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

// Copy an ASCII string into a `Buffer` one byte at a time.
// (This only works for ASCII-only strings. In general, one should use
// `Buffer.from()` to perform this conversion.)

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

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

console.log(buf.toString('utf8'));
// Prints: Node.js
```

### `buf.buffer`

* {ArrayBuffer} The underlying `ArrayBuffer` object based on which this `Buffer`
  object is created.

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

```mjs
import { Buffer } from 'node:buffer';

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

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

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

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

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

### `buf.byteOffset`

* {integer} The `byteOffset` of the `Buffer`s underlying `ArrayBuffer` object.

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

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

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

```mjs
import { Buffer } from 'node:buffer';

// Create a buffer smaller than `Buffer.poolSize`.
const nodeBuffer = Buffer.from([0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);

// When casting the Node.js Buffer to an Int8Array, use the byteOffset
// to refer only to the part of `nodeBuffer.buffer` that contains the memory
// for `nodeBuffer`.
new Int8Array(nodeBuffer.buffer, nodeBuffer.byteOffset, nodeBuffer.length);
```

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

// Create a buffer smaller than `Buffer.poolSize`.
const nodeBuffer = Buffer.from([0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);

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

* `target` {Buffer|Uint8Array} A `Buffer` or [`Uint8Array`][] with which to
  compare `buf`.
* `targetStart` {integer} The offset within `target` at which to begin
  comparison. **Default:** `0`.
* `targetEnd` {integer} The offset within `target` at which to end comparison
  (not inclusive). **Default:** `target.length`.
* `sourceStart` {integer} The offset within `buf` at which to begin comparison.
  **Default:** `0`.
* `sourceEnd` {integer} The offset within `buf` at which to end comparison
  (not inclusive). **Default:** [`buf.length`][].
* Returns: {integer}

Compares `buf` with `target` and returns a number indicating whether `buf`
comes before, after, or is the same as `target` in sort order.
Comparison is based on the actual sequence of bytes in each `Buffer`.

* `0` is returned 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.

```mjs
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));
// 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].)
```

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

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

The optional `targetStart`, `targetEnd`, `sourceStart`, and `sourceEnd`
arguments can be used to limit the comparison to specific ranges within `target`
and `buf` respectively.

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

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

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

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

* `target` {Buffer|Uint8Array} A `Buffer` or [`Uint8Array`][] to copy into.
* `targetStart` {integer} The offset within `target` at which to begin
  writing. **Default:** `0`.
* `sourceStart` {integer} The offset within `buf` from which to begin copying.
  **Default:** `0`.
* `sourceEnd` {integer} The offset within `buf` at which to stop copying (not
  inclusive). **Default:** [`buf.length`][].
* Returns: {integer} The number of bytes copied.

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

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

```mjs
import { Buffer } from 'node: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!!!!!!!!!!!!!
```

```cjs
const { Buffer } = require('node: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!!!!!!!!!!!!!
```

```mjs
import { Buffer } from 'node: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
```

```cjs
const { Buffer } = require('node: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
```

### `buf.entries()`

* Returns: {Iterator}

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

```mjs
import { Buffer } from 'node: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]
```

```cjs
const { Buffer } = require('node: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]
```

### `buf.equals(otherBuffer)`

* `otherBuffer` {Buffer|Uint8Array} A `Buffer` or [`Uint8Array`][] with which to
  compare `buf`.
* Returns: {boolean}

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

```mjs
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));
// Prints: true
console.log(buf1.equals(buf3));
// Prints: false
```

```cjs
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));
// Prints: true
console.log(buf1.equals(buf3));
// Prints: false
```

### `buf.fill(value[, offset[, end]][, encoding])`

* `value` {string|Buffer|Uint8Array|integer} The value with which to fill `buf`.
  Empty value (string, Uint8Array, Buffer) is coerced to `0`.
* `offset` {integer} Number of bytes to skip before starting to fill `buf`.
  **Default:** `0`.
* `end` {integer} Where to stop filling `buf` (not inclusive). **Default:**
  [`buf.length`][].
* `encoding` {string} The encoding for `value` if `value` is a string.
  **Default:** `'utf8'`.
* Returns: {Buffer} A reference to `buf`.

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

```mjs
import { Buffer } from 'node:buffer';

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

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

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

// Fill a buffer with empty string
const c = Buffer.allocUnsafe(5).fill('');

console.log(c.fill(''));
// Prints: <Buffer 00 00 00 00 00>
```

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

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

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

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

// Fill a buffer with empty string
const c = Buffer.allocUnsafe(5).fill('');

console.log(c.fill(''));
// Prints: <Buffer 00 00 00 00 00>
```

`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:

```mjs
import { Buffer } from 'node: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>
```

```cjs
const { Buffer } = require('node: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:

```mjs
import { Buffer } from 'node: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.
```

```cjs
const { Buffer } = require('node: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.
```

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

* `value` {string|Buffer|Uint8Array|integer} What to search for.
* `byteOffset` {integer} Where to begin searching in `buf`. If negative, then
  offset is calculated from the end of `buf`. **Default:** `0`.
* `encoding` {string} If `value` is a string, this is its encoding.
  **Default:** `'utf8'`.
* Returns: {boolean} `true` if `value` was found in `buf`, `false` otherwise.

Equivalent to [`buf.indexOf() !== -1`][`buf.indexOf()`].

```mjs
import { Buffer } from 'node: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
```

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

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

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

* `value` {string|Buffer|Uint8Array|integer} What to search for.
* `byteOffset` {integer} Where to begin searching in `buf`. If negative, then
  offset is calculated from the end of `buf`. **Default:** `0`.
* `encoding` {string} If `value` is a string, this is the encoding used to
  determine the binary representation of the string that will be searched for in
  `buf`. **Default:** `'utf8'`.
* Returns: {integer} The index of the first occurrence of `value` in `buf`, or
  `-1` if `buf` does not contain `value`.

If `value` is:

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

```mjs
import { Buffer } from 'node: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
```

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

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

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

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

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

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

```mjs
import { Buffer } from 'node: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', []));
```

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

If `value` is an empty string or empty `Buffer` and `byteOffset` is less
than `buf.length`, `byteOffset` will be returned. If `value` is empty and
`byteOffset` is at least `buf.length`, `buf.length` will be returned.

### `buf.keys()`

* Returns: {Iterator}

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

```mjs
import { Buffer } from 'node:buffer';

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

for (const key of buf.keys()) {
  console.log(key);
}
// Prints:
//   0
//   1
//   2
//   3
//   4
//   5
```

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

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

for (const key of buf.keys()) {
  console.log(key);
}
// Prints:
//   0
//   1
//   2
//   3
//   4
//   5
```

### `buf.lastIndexOf(value[, byteOffset][, encoding])`

* `value` {string|Buffer|Uint8Array|integer} What to search for.
* `byteOffset` {integer} Where to begin searching in `buf`. If negative, then
  offset is calculated from the end of `buf`. **Default:**
  `buf.length - 1`.
* `encoding` {string} If `value` is a string, this is the encoding used to
  determine the binary representation of the string that will be searched for in
  `buf`. **Default:** `'utf8'`.
* Returns: {integer} The index of the last occurrence of `value` in `buf`, or
  `-1` if `buf` does not contain `value`.

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

```mjs
import { Buffer } from 'node: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
```

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

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

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

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

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

If `byteOffset` is not a number, it will be coerced to a number. Any arguments
that coerce to `NaN`, like `{}` or `undefined`, will search the whole buffer.
This behavior matches [`String.prototype.lastIndexOf()`][].

```mjs
import { Buffer } from 'node: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', []));
```

```cjs
const { Buffer } = require('node: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.

### `buf.length`

* {integer}

Returns the number of bytes in `buf`.

```mjs
import { Buffer } from 'node:buffer';

// Create a `Buffer` and write a shorter string to it using UTF-8.

const buf = Buffer.alloc(1234);

console.log(buf.length);
// Prints: 1234

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

console.log(buf.length);
// Prints: 1234
```

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

// Create a `Buffer` and write a shorter string to it using UTF-8.

const buf = Buffer.alloc(1234);

console.log(buf.length);
// Prints: 1234

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

console.log(buf.length);
// Prints: 1234
```

### `buf.parent`

> Stability: 0 - Deprecated: Use [`buf.buffer`][] instead.

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

### `buf.readBigInt64BE([offset])`

* `offset` {integer} Number of bytes to skip before starting to read. Must
 satisfy: `0 <= offset <= buf.length - 8`. **Default:** `0`.
* Returns: {bigint}

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

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

### `buf.readBigInt64LE([offset])`

* `offset` {integer} Number of bytes to skip before starting to read. Must
 satisfy: `0 <= offset <= buf.length - 8`. **Default:** `0`.
* Returns: {bigint}

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

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

### `buf.readBigUInt64BE([offset])`

* `offset` {integer} Number of bytes to skip before starting to read. Must
 satisfy: `0 <= offset <= buf.length - 8`. **Default:** `0`.
* Returns: {bigint}

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

This function is also available under the `readBigUint64BE` alias.

```mjs
import { Buffer } from 'node:buffer';

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

console.log(buf.readBigUInt64BE(0));
// Prints: 4294967295n
```

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

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

console.log(buf.readBigUInt64BE(0));
// Prints: 4294967295n
```

### `buf.readBigUInt64LE([offset])`

* `offset` {integer} Number of bytes to skip before starting to read. Must
 satisfy: `0 <= offset <= buf.length - 8`. **Default:** `0`.
* Returns: {bigint}

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

This function is also available under the `readBigUint64LE` alias.

```mjs
import { Buffer } from 'node:buffer';

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

console.log(buf.readBigUInt64LE(0));
// Prints: 18446744069414584320n
```

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

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

console.log(buf.readBigUInt64LE(0));
// Prints: 18446744069414584320n
```

### `buf.readDoubleBE([offset])`

* `offset` {integer} Number of bytes to skip before starting to read. Must
 satisfy `0 <= offset <= buf.length - 8`. **Default:** `0`.
* Returns: {number}

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

```mjs
import { Buffer } from 'node:buffer';

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

console.log(buf.readDoubleBE(0));
// Prints: 8.20788039913184e-304
```

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

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

console.log(buf.readDoubleBE(0));
// Prints: 8.20788039913184e-304
```

### `buf.readDoubleLE([offset])`

* `offset` {integer} Number of bytes to skip before starting to read. Must
 satisfy `0 <= offset <= buf.length - 8`. **Default:** `0`.
* Returns: {number}

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

```mjs
import { Buffer } from 'node: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.
```

```cjs
const { Buffer } = require('node: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.
```

### `buf.readFloatBE([offset])`

* `offset` {integer} Number of bytes to skip before starting to read. Must
 satisfy `0 <= offset <= buf.length - 4`. **Default:** `0`.
* Returns: {number}

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

```mjs
import { Buffer } from 'node:buffer';

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

console.log(buf.readFloatBE(0));
// Prints: 2.387939260590663e-38
```

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

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

console.log(buf.readFloatBE(0));
// Prints: 2.387939260590663e-38
```

### `buf.readFloatLE([offset])`

* `offset` {integer} Number of bytes to skip before starting to read. Must
 satisfy `0 <= offset <= buf.length - 4`. **Default:** `0`.
* Returns: {number}

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

```mjs
import { Buffer } from 'node: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.
```

```cjs
const { Buffer } = require('node: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.
```

### `buf.readInt8([offset])`

* `offset` {integer} Number of bytes to skip before starting to read. Must
 satisfy `0 <= offset <= buf.length - 1`. **Default:** `0`.
* Returns: {integer}

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

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

```mjs
import { Buffer } from 'node: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.
```

```cjs
const { Buffer } = require('node: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.
```

### `buf.readInt16BE([offset])`

* `offset` {integer} Number of bytes to skip before starting to read. Must
 satisfy `0 <= offset <= buf.length - 2`. **Default:** `0`.
* Returns: {integer}

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

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

```mjs
import { Buffer } from 'node:buffer';

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

console.log(buf.readInt16BE(0));
// Prints: 5
```

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

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

console.log(buf.readInt16BE(0));
// Prints: 5
```

### `buf.readInt16LE([offset])`

* `offset` {integer} Number of bytes to skip before starting to read. Must
 satisfy `0 <= offset <= buf.length - 2`. **Default:** `0`.
* Returns: {integer}

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

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

```mjs
import { Buffer } from 'node:buffer';

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

console.log(buf.readInt16LE(0));
// Prints: 1280
console.log(buf.readInt16LE(1));
// Throws ERR_OUT_OF_RANGE.
```

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

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

console.log(buf.readInt16LE(0));
// Prints: 1280
console.log(buf.readInt16LE(1));
// Throws ERR_OUT_OF_RANGE.
```

### `buf.readInt32BE([offset])`

* `offset` {integer} Number of bytes to skip before starting to read. Must
 satisfy `0 <= offset <= buf.length - 4`. **Default:** `0`.
* Returns: {integer}

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

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

```mjs
import { Buffer } from 'node:buffer';

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

console.log(buf.readInt32BE(0));
// Prints: 5
```

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

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

console.log(buf.readInt32BE(0));
// Prints: 5
```

### `buf.readInt32LE([offset])`

* `offset` {integer} Number of bytes to skip before starting to read. Must
 satisfy `0 <= offset <= buf.length - 4`. **Default:** `0`.
* Returns: {integer}

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

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

```mjs
import { Buffer } from 'node: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.
```

```cjs
const { Buffer } = require('node: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.
```

### `buf.readIntBE(offset, byteLength)`

* `offset` {integer} Number of bytes to skip before starting to read. Must
 satisfy `0 <= offset <= buf.length - byteLength`.
* `byteLength` {integer} Number of bytes to read. Must satisfy
 `0 < byteLength <= 6`.
* Returns: {integer}

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

```mjs
import { Buffer } from 'node: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.
```

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

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

### `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.

```mjs
import { Buffer } from 'node:buffer';

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

console.log(buf.readIntLE(0, 6).toString(16));
// Prints: -546f87a9cbee
```

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

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

console.log(buf.readIntLE(0, 6).toString(16));
// Prints: -546f87a9cbee
```

### `buf.readUInt8([offset])`

* `offset` {integer} Number of bytes to skip before starting to read. Must
 satisfy `0 <= offset <= buf.length - 1`. **Default:** `0`.
* Returns: {integer}

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

This function is also available under the `readUint8` alias.

```mjs
import { Buffer } from 'node: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.
```

```cjs
const { Buffer } = require('node: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.
```

### `buf.readUInt16BE([offset])`

* `offset` {integer} Number of bytes to skip before starting to read. Must
 satisfy `0 <= offset <= buf.length - 2`. **Default:** `0`.
* Returns: {integer}

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

This function is also available under the `readUint16BE` alias.

```mjs
import { Buffer } from 'node: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
```

```cjs
const { Buffer } = require('node: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
```

### `buf.readUInt16LE([offset])`

* `offset` {integer} Number of bytes to skip before starting to read. Must
 satisfy `0 <= offset <= buf.length - 2`. **Default:** `0`.
* Returns: {integer}

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

This function is also available under the `readUint16LE` alias.

```mjs
import { Buffer } from 'node: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.
```

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

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

### `buf.readUInt32BE([offset])`

* `offset` {integer} Number of bytes to skip before starting to read. Must
 satisfy `0 <= offset <= buf.length - 4`. **Default:** `0`.
* Returns: {integer}

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

This function is also available under the `readUint32BE` alias.

```mjs
import { Buffer } from 'node:buffer';

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

console.log(buf.readUInt32BE(0).toString(16));
// Prints: 12345678
```

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

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

console.log(buf.readUInt32BE(0).toString(16));
// Prints: 12345678
```

### `buf.readUInt32LE([offset])`

* `offset` {integer} Number of bytes to skip before starting to read. Must
 satisfy `0 <= offset <= buf.length - 4`. **Default:** `0`.
* Returns: {integer}

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

This function is also available under the `readUint32LE` alias.

```mjs
import { Buffer } from 'node: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.
```

```cjs
const { Buffer } = require('node: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.
```

### `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.

```mjs
import { Buffer } from 'node: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.
```

```cjs
const { Buffer } = require('node: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.
```

### `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.

```mjs
import { Buffer } from 'node:buffer';

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

console.log(buf.readUIntLE(0, 6).toString(16));
// Prints: ab9078563412
```

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

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

console.log(buf.readUIntLE(0, 6).toString(16));
// Prints: ab9078563412
```

### `buf.subarray([start[, end]])`

* `start` {integer} Where the new `Buffer` will start. **Default:** `0`.
* `end` {integer} Where the new `Buffer` will end (not inclusive).
  **Default:** [`buf.length`][].
* Returns: {Buffer}

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

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

This method is inherited from [`TypedArray.prototype.subarray()`][].

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

```mjs
import { Buffer } from 'node: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
```

```cjs
const { Buffer } = require('node: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.

```mjs
import { Buffer } from 'node: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).)
```

```cjs
const { Buffer } = require('node: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).)
```

### `buf.slice([start[, end]])`

* `start` {integer} Where the new `Buffer` will start. **Default:** `0`.
* `end` {integer} Where the new `Buffer` will end (not inclusive).
  **Default:** [`buf.length`][].
* Returns: {Buffer}

> Stability: 0 - Deprecated: Use [`buf.subarray`][] instead.

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

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

```mjs
import { Buffer } from 'node: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

// With buf.slice(), the original buffer is modified.
const notReallyCopiedBuf = buf.slice();
notReallyCopiedBuf[0]++;
console.log(notReallyCopiedBuf.toString());
// Prints: cuffer
console.log(buf.toString());
// Also prints: cuffer (!)
```

```cjs
const { Buffer } = require('node: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

### `buf.swap16()`

* Returns: {Buffer} A reference to `buf`.

Interprets `buf` as an array of unsigned 16-bit integers and swaps the
byte order _in-place_. Throws [`ERR_INVALID_BUFFER_SIZE`][] if [`buf.length`][]
is not a multiple of 2.

```mjs
import { Buffer } from 'node: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.
```

```cjs
const { Buffer } = require('node: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:

```mjs
import { Buffer } from 'node:buffer';

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

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

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

### `buf.swap32()`

* Returns: {Buffer} A reference to `buf`.

Interprets `buf` as an array of unsigned 32-bit integers and swaps the
byte order _in-place_. Throws [`ERR_INVALID_BUFFER_SIZE`][] if [`buf.length`][]
is not a multiple of 4.

```mjs
import { Buffer } from 'node: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.
```

```cjs
const { Buffer } = require('node: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.
```

### `buf.swap64()`

* Returns: {Buffer} A reference to `buf`.

Interprets `buf` as an array of 64-bit numbers and swaps byte order _in-place_.
Throws [`ERR_INVALID_BUFFER_SIZE`][] if [`buf.length`][] is not a multiple of 8.

```mjs
import { Buffer } from 'node: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.
```

```cjs
const { Buffer } = require('node: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.
```

### `buf.toJSON()`

* Returns: {Object}

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

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

```mjs
import { Buffer } from 'node: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 && value.type === 'Buffer' ?
    Buffer.from(value) :
    value;
});

console.log(copy);
// Prints: <Buffer 01 02 03 04 05>
```

```cjs
const { Buffer } = require('node: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 && value.type === 'Buffer' ?
    Buffer.from(value) :
    value;
});

console.log(copy);
// Prints: <Buffer 01 02 03 04 05>
```

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

* `encoding` {string} The character encoding to use. **Default:** `'utf8'`.
* `start` {integer} The byte offset to start decoding at. **Default:** `0`.
* `end` {integer} The byte offset to stop decoding at (not inclusive).
  **Default:** [`buf.length`][].
* Returns: {string}

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

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

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

```mjs
import { Buffer } from 'node: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
```

```cjs
const { Buffer } = require('node: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
```

### `buf.values()`

* Returns: {Iterator}

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

```mjs
import { Buffer } from 'node: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
```

```cjs
const { Buffer } = require('node: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
```

### `buf.write(string[, offset[, length]][, encoding])`

* `string` {string} String to write to `buf`.
* `offset` {integer} Number of bytes to skip before starting to write `string`.
  **Default:** `0`.
* `length` {integer} Maximum number of bytes to write (written bytes will not
  exceed `buf.length - offset`). **Default:** `buf.length - offset`.
* `encoding` {string} The character encoding of `string`. **Default:** `'utf8'`.
* Returns: {integer} Number of bytes written.

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

```mjs
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)}`);
// 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
```

```cjs
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)}`);
// Prints: 12 bytes: ½ + ¼ = ¾

const buffer = Buffer.alloc(10);

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

console.log(`${length} bytes: ${buffer.toString('utf8', 8, 10)}`);
// Prints: 2 bytes : ab
```

### `buf.writeBigInt64BE(value[, offset])`

* `value` {bigint} Number to be written to `buf`.
* `offset` {integer} Number of bytes to skip before starting to write. Must
 satisfy: `0 <= offset <= buf.length - 8`. **Default:** `0`.
* Returns: {integer} `offset` plus the number of bytes written.

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

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

```mjs
import { Buffer } from 'node:buffer';

const buf = Buffer.allocUnsafe(8);

buf.writeBigInt64BE(0x0102030405060708n, 0);

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

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

const buf = Buffer.allocUnsafe(8);

buf.writeBigInt64BE(0x0102030405060708n, 0);

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

### `buf.writeBigInt64LE(value[, offset])`

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

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

```mjs
import { Buffer } from 'node:buffer';

const buf = Buffer.allocUnsafe(8);

buf.writeBigInt64LE(0x0102030405060708n, 0);

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

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

const buf = Buffer.allocUnsafe(8);

buf.writeBigInt64LE(0x0102030405060708n, 0);

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

### `buf.writeBigUInt64BE(value[, offset])`

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

This function is also available under the `writeBigUint64BE` alias.

```mjs
import { Buffer } from 'node:buffer';

const buf = Buffer.allocUnsafe(8);

buf.writeBigUInt64BE(0xdecafafecacefaden, 0);

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

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

const buf = Buffer.allocUnsafe(8);

buf.writeBigUInt64BE(0xdecafafecacefaden, 0);

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

### `buf.writeBigUInt64LE(value[, offset])`

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

```mjs
import { Buffer } from 'node:buffer';

const buf = Buffer.allocUnsafe(8);

buf.writeBigUInt64LE(0xdecafafecacefaden, 0);

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

```cjs
const { Buffer } = require('node: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.

### `buf.writeDoubleBE(value[, offset])`

* `value` {number} Number to be written to `buf`.
* `offset` {integer} Number of bytes to skip before starting to write. Must
 satisfy `0 <= offset <= buf.length - 8`. **Default:** `0`.
* Returns: {integer} `offset` plus the number of bytes written.

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

```mjs
import { Buffer } from 'node:buffer';

const buf = Buffer.allocUnsafe(8);

buf.writeDoubleBE(123.456, 0);

console.log(buf);
// Prints: <Buffer 40 5e dd 2f 1a 9f be 77>
```

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

const buf = Buffer.allocUnsafe(8);

buf.writeDoubleBE(123.456, 0);

console.log(buf);
// Prints: <Buffer 40 5e dd 2f 1a 9f be 77>
```

### `buf.writeDoubleLE(value[, offset])`

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.

```mjs
import { Buffer } from 'node:buffer';

const buf = Buffer.allocUnsafe(8);

buf.writeDoubleLE(123.456, 0);

console.log(buf);
// Prints: <Buffer 77 be 9f 1a 2f dd 5e 40>
```

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

const buf = Buffer.allocUnsafe(8);

buf.writeDoubleLE(123.456, 0);

console.log(buf);
// Prints: <Buffer 77 be 9f 1a 2f dd 5e 40>
```

### `buf.writeFloatBE(value[, offset])`

* `value` {number} Number to be written to `buf`.
* `offset` {integer} Number of bytes to skip before starting to write. Must
 satisfy `0 <= offset <= buf.length - 4`. **Default:** `0`.
* Returns: {integer} `offset` plus the number of bytes written.

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

```mjs
import { Buffer } from 'node:buffer';

const buf = Buffer.allocUnsafe(4);

buf.writeFloatBE(0xcafebabe, 0);

console.log(buf);
// Prints: <Buffer 4f 4a fe bb>
```

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

const buf = Buffer.allocUnsafe(4);

buf.writeFloatBE(0xcafebabe, 0);

console.log(buf);
// Prints: <Buffer 4f 4a fe bb>
```

### `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.

```mjs
import { Buffer } from 'node:buffer';

const buf = Buffer.allocUnsafe(4);

buf.writeFloatLE(0xcafebabe, 0);

console.log(buf);
// Prints: <Buffer bb fe 4a 4f>
```

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

const buf = Buffer.allocUnsafe(4);

buf.writeFloatLE(0xcafebabe, 0);

console.log(buf);
// Prints: <Buffer bb fe 4a 4f>
```

### `buf.writeInt8(value[, offset])`

* `value` {integer} Number to be written to `buf`.
* `offset` {integer} Number of bytes to skip before starting to write. Must
 satisfy `0 <= offset <= buf.length - 1`. **Default:** `0`.
* Returns: {integer} `offset` plus the number of bytes written.

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

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

```mjs
import { Buffer } from 'node:buffer';

const buf = Buffer.allocUnsafe(2);

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

console.log(buf);
// Prints: <Buffer 02 fe>
```

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

const buf = Buffer.allocUnsafe(2);

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

console.log(buf);
// Prints: <Buffer 02 fe>
```

### `buf.writeInt16BE(value[, offset])`

* `value` {integer} Number to be written to `buf`.
* `offset` {integer} Number of bytes to skip before starting to write. Must
 satisfy `0 <= offset <= buf.length - 2`. **Default:** `0`.
* Returns: {integer} `offset` plus the number of bytes written.

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

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

```mjs
import { Buffer } from 'node:buffer';

const buf = Buffer.allocUnsafe(2);

buf.writeInt16BE(0x0102, 0);

console.log(buf);
// Prints: <Buffer 01 02>
```

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

const buf = Buffer.allocUnsafe(2);

buf.writeInt16BE(0x0102, 0);

console.log(buf);
// Prints: <Buffer 01 02>
```

### `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.

```mjs
import { Buffer } from 'node:buffer';

const buf = Buffer.allocUnsafe(2);

buf.writeInt16LE(0x0304, 0);

console.log(buf);
// Prints: <Buffer 04 03>
```

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

const buf = Buffer.allocUnsafe(2);

buf.writeInt16LE(0x0304, 0);

console.log(buf);
// Prints: <Buffer 04 03>
```

### `buf.writeInt32BE(value[, offset])`

* `value` {integer} Number to be written to `buf`.
* `offset` {integer} Number of bytes to skip before starting to write. Must
 satisfy `0 <= offset <= buf.length - 4`. **Default:** `0`.
* Returns: {integer} `offset` plus the number of bytes written.

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

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

```mjs
import { Buffer } from 'node:buffer';

const buf = Buffer.allocUnsafe(4);

buf.writeInt32BE(0x01020304, 0);

console.log(buf);
// Prints: <Buffer 01 02 03 04>
```

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

const buf = Buffer.allocUnsafe(4);

buf.writeInt32BE(0x01020304, 0);

console.log(buf);
// Prints: <Buffer 01 02 03 04>
```

### `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.

```mjs
import { Buffer } from 'node:buffer';

const buf = Buffer.allocUnsafe(4);

buf.writeInt32LE(0x05060708, 0);

console.log(buf);
// Prints: <Buffer 08 07 06 05>
```

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

const buf = Buffer.allocUnsafe(4);

buf.writeInt32LE(0x05060708, 0);

console.log(buf);
// Prints: <Buffer 08 07 06 05>
```

### `buf.writeIntBE(value, offset, byteLength)`

* `value` {integer} Number to be written to `buf`.
* `offset` {integer} Number of bytes to skip before starting to write. Must
 satisfy `0 <= offset <= buf.length - byteLength`.
* `byteLength` {integer} Number of bytes to write. Must satisfy
 `0 < byteLength <= 6`.
* Returns: {integer} `offset` plus the number of bytes written.

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

```mjs
import { Buffer } from 'node:buffer';

const buf = Buffer.allocUnsafe(6);

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

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

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

const buf = Buffer.allocUnsafe(6);

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

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

### `buf.writeIntLE(value, offset, byteLength)`

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.

```mjs
import { Buffer } from 'node:buffer';

const buf = Buffer.allocUnsafe(6);

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

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

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

const buf = Buffer.allocUnsafe(6);

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

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

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

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.

```mjs
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);
// Prints: <Buffer 03 04 23 42>
```

```cjs
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);
// Prints: <Buffer 03 04 23 42>
```

### `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.

```mjs
import { Buffer } from 'node:buffer';

const buf = Buffer.allocUnsafe(4);

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

console.log(buf);
// Prints: <Buffer de ad be ef>
```

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

const buf = Buffer.allocUnsafe(4);

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

console.log(buf);
// Prints: <Buffer de ad be ef>
```

### `buf.writeUInt16LE(value[, offset])`

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.

```mjs
import { Buffer } from 'node:buffer';

const buf = Buffer.allocUnsafe(4);

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

console.log(buf);
// Prints: <Buffer ad de ef be>
```

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

const buf = Buffer.allocUnsafe(4);

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

console.log(buf);
// Prints: <Buffer ad de ef be>
```

### `buf.writeUInt32BE(value[, offset])`

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.

```mjs
import { Buffer } from 'node:buffer';

const buf = Buffer.allocUnsafe(4);

buf.writeUInt32BE(0xfeedface, 0);

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

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

const buf = Buffer.allocUnsafe(4);

buf.writeUInt32BE(0xfeedface, 0);

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

### `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.

```mjs
import { Buffer } from 'node:buffer';

const buf = Buffer.allocUnsafe(4);

buf.writeUInt32LE(0xfeedface, 0);

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

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

const buf = Buffer.allocUnsafe(4);

buf.writeUInt32LE(0xfeedface, 0);

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

### `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.

```mjs
import { Buffer } from 'node:buffer';

const buf = Buffer.allocUnsafe(6);

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

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

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

const buf = Buffer.allocUnsafe(6);

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

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

### `buf.writeUIntLE(value, offset, byteLength)`

This function is also available under the `writeUintLE` alias.

```mjs
import { Buffer } from 'node:buffer';

const buf = Buffer.allocUnsafe(6);

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

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

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

const buf = Buffer.allocUnsafe(6);

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

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

### `new Buffer(array)`

> Stability: 0 - Deprecated: Use [`Buffer.from(array)`][] instead.

* `array` {integer\[]} An array of bytes to copy from.

See [`Buffer.from(array)`][].

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

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

* `arrayBuffer` {ArrayBuffer|SharedArrayBuffer} An [`ArrayBuffer`][],
  [`SharedArrayBuffer`][] or the `.buffer` property of a [`TypedArray`][].
* `byteOffset` {integer} Index of first byte to expose. **Default:** `0`.
* `length` {integer} Number of bytes to expose.
  **Default:** `arrayBuffer.byteLength - byteOffset`.

See
[`Buffer.from(arrayBuffer[, byteOffset[, length]])`][`Buffer.from(arrayBuf)`].

### `new Buffer(buffer)`

> Stability: 0 - Deprecated: Use [`Buffer.from(buffer)`][] instead.

* `buffer` {Buffer|Uint8Array} An existing `Buffer` or [`Uint8Array`][] from
  which to copy data.

See [`Buffer.from(buffer)`][].

### `new Buffer(size)`

> Stability: 0 - Deprecated: Use [`Buffer.alloc()`][] instead (also see
> [`Buffer.allocUnsafe()`][]).

* `size` {integer} The desired length of the new `Buffer`.

See [`Buffer.alloc()`][] and [`Buffer.allocUnsafe()`][]. This variant of the
constructor is equivalent to [`Buffer.alloc()`][].

### `new Buffer(string[, encoding])`

> Stability: 0 - Deprecated:
> Use [`Buffer.from(string[, encoding])`][`Buffer.from(string)`] instead.

* `string` {string} String to encode.
* `encoding` {string} The encoding of `string`. **Default:** `'utf8'`.

See [`Buffer.from(string[, encoding])`][`Buffer.from(string)`].

## Class: `File`

> Stability: 1 - Experimental

* Extends: {Blob}

A [`File`][] provides information about files.

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

* `sources` {string\[]|ArrayBuffer\[]|TypedArray\[]|DataView\[]|Blob\[]|File\[]}
  An array of string, {ArrayBuffer}, {TypedArray}, {DataView}, {File}, or {Blob}
  objects, or any mix of such objects, that will be stored within the `File`.
* `fileName` {string} The name of the file.
* `options` {Object}
  * `endings` {string} One of either `'transparent'` or `'native'`. When set
    to `'native'`, line endings in string source parts will be converted to
    the platform native line-ending as specified by `require('node:os').EOL`.
  * `type` {string} The File content-type.
  * `lastModified` {number} The last modified date of the file.
    **Default:** `Date.now()`.

### `file.name`

* Type: {string}

The name of the `File`.

### `file.lastModified`

* Type: {number}

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)`

> Stability: 3 - Legacy. Use `Buffer.from(data, 'base64')` instead.

* `data` {any} The Base64-encoded input string.

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)`

> Stability: 3 - Legacy. Use `buf.toString('base64')` instead.

* `data` {any} An ASCII (Latin1) string.

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.

### `buffer.isAscii(input)`

* input {Buffer | ArrayBuffer | TypedArray} The input to validate.
* Returns: {boolean}

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)`

* input {Buffer | ArrayBuffer | TypedArray} The input to validate.
* Returns: {boolean}

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`

* {integer} **Default:** `50`

Returns the maximum number of bytes that will be returned when
`buf.inspect()` is called. This can be overridden by user modules. See
[`util.inspect()`][] for more details on `buf.inspect()` behavior.

### `buffer.kMaxLength`

* {integer} The largest size allowed for a single `Buffer` instance.

An alias for [`buffer.constants.MAX_LENGTH`][].

### `buffer.kStringMaxLength`

* {integer} The largest length allowed for a single `string` instance.

An alias for [`buffer.constants.MAX_STRING_LENGTH`][].

### `buffer.resolveObjectURL(id)`

> Stability: 1 - Experimental

* `id` {string} A `'blob:nodedata:...` URL string returned by a prior call to
  `URL.createObjectURL()`.
* Returns: {Blob}

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

### `buffer.transcode(source, fromEnc, toEnc)`

* `source` {Buffer|Uint8Array} A `Buffer` or `Uint8Array` instance.
* `fromEnc` {string} The current encoding.
* `toEnc` {string} To target encoding.
* Returns: {Buffer}

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

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

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

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

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

const newBuf = transcode(Buffer.from('€'), 'utf8', 'ascii');
console.log(newBuf.toString('ascii'));
// Prints: '?'
```

```cjs
const { Buffer, transcode } = require('node:buffer');

const newBuf = transcode(Buffer.from('€'), 'utf8', 'ascii');
console.log(newBuf.toString('ascii'));
// Prints: '?'
```

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

### Class: `SlowBuffer`

> Stability: 0 - Deprecated: Use [`Buffer.allocUnsafeSlow()`][] instead.

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

#### `new SlowBuffer(size)`

> Stability: 0 - Deprecated: Use [`Buffer.allocUnsafeSlow()`][] instead.

* `size` {integer} The desired length of the new `SlowBuffer`.

See [`Buffer.allocUnsafeSlow()`][].

### Buffer constants

#### `buffer.constants.MAX_LENGTH`

* {integer} The largest size allowed for a single `Buffer` instance.

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

On 64-bit architectures, this value currently is 232 (about 4 GiB).

It reflects [`v8::TypedArray::kMaxLength`][] under the hood.

This value is also available as [`buffer.kMaxLength`][].

#### `buffer.constants.MAX_STRING_LENGTH`

* {integer} The largest length allowed for a single `string` instance.

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

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

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

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

* Passing a number as the first argument to `Buffer()` (e.g. `new Buffer(10)`)
  allocates a new `Buffer` object of the specified size. Prior to Node.js 8.0.0,
  the memory allocated for such `Buffer` instances is _not_ initialized and
  _can contain sensitive data_. Such `Buffer` instances _must_ be subsequently
  initialized by using either [`buf.fill(0)`][`buf.fill()`] or by writing to the
  entire `Buffer` before reading data from the `Buffer`.
  While this behavior is _intentional_ to improve performance,
  development experience has demonstrated that a more explicit distinction is
  required between creating a fast-but-uninitialized `Buffer` versus creating a
  slower-but-safer `Buffer`. Since Node.js 8.0.0, `Buffer(num)` and `new
  Buffer(num)` return a `Buffer` with initialized memory.
* Passing a string, array, or `Buffer` as the first argument copies the
  passed object's data into the `Buffer`.
* Passing an [`ArrayBuffer`][] or a [`SharedArrayBuffer`][] returns a `Buffer`
  that shares allocated memory with the given array buffer.

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

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

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

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

* [`Buffer.from(array)`][] returns a new `Buffer` that _contains a copy_ of the
  provided octets.
* [`Buffer.from(arrayBuffer[, byteOffset[, length]])`][`Buffer.from(arrayBuf)`]
  returns a new `Buffer` that _shares the same allocated memory_ as the given
  [`ArrayBuffer`][].
* [`Buffer.from(buffer)`][] returns a new `Buffer` that _contains a copy_ of the
  contents of the given `Buffer`.
* [`Buffer.from(string[, encoding])`][`Buffer.from(string)`] returns a new
  `Buffer` that _contains a copy_ of the provided string.
* [`Buffer.alloc(size[, fill[, encoding]])`][`Buffer.alloc()`] returns a new
  initialized `Buffer` of the specified size. This method is slower than
  [`Buffer.allocUnsafe(size)`][`Buffer.allocUnsafe()`] but guarantees that newly
  created `Buffer` instances never contain old data that is potentially
  sensitive. A `TypeError` will be thrown if `size` is not a number.
* [`Buffer.allocUnsafe(size)`][`Buffer.allocUnsafe()`] and
  [`Buffer.allocUnsafeSlow(size)`][`Buffer.allocUnsafeSlow()`] each return a
  new uninitialized `Buffer` of the specified `size`. Because the `Buffer` is
  uninitialized, the allocated segment of memory might contain old data that is
  potentially sensitive.

`Buffer` instances returned by [`Buffer.allocUnsafe()`][] and
[`Buffer.from(array)`][] _may_ be allocated off a shared internal memory pool
if `size` is less than or equal to half [`Buffer.poolSize`][]. Instances
returned by [`Buffer.allocUnsafeSlow()`][] _never_ use the shared internal
memory pool.

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

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

```console
$ 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.

[ASCII]: https://en.wikipedia.org/wiki/ASCII
[Base64]: https://en.wikipedia.org/wiki/Base64
[ISO-8859-1]: https://en.wikipedia.org/wiki/ISO-8859-1
[RFC 4648, Section 5]: https://tools.ietf.org/html/rfc4648#section-5
[UTF-16]: https://en.wikipedia.org/wiki/UTF-16
[UTF-8]: https://en.wikipedia.org/wiki/UTF-8
[WHATWG Encoding Standard]: https://encoding.spec.whatwg.org/
[`ArrayBuffer`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer
[`Blob`]: https://developer.mozilla.org/en-US/docs/Web/API/Blob
[`Buffer.alloc()`]: #static-method-bufferallocsize-fill-encoding
[`Buffer.allocUnsafe()`]: #static-method-bufferallocunsafesize
[`Buffer.allocUnsafeSlow()`]: #static-method-bufferallocunsafeslowsize
[`Buffer.concat()`]: #static-method-bufferconcatlist-totallength
[`Buffer.copyBytesFrom()`]: #static-method-buffercopybytesfromview-offset-length
[`Buffer.from(array)`]: #static-method-bufferfromarray
[`Buffer.from(arrayBuf)`]: #static-method-bufferfromarraybuffer-byteoffset-length
[`Buffer.from(buffer)`]: #static-method-bufferfrombuffer
[`Buffer.from(string)`]: #static-method-bufferfromstring-encoding
[`Buffer.poolSize`]: #class-property-bufferpoolsize
[`DataView`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView
[`ERR_INVALID_BUFFER_SIZE`]: errors.md#err_invalid_buffer_size
[`ERR_OUT_OF_RANGE`]: errors.md#err_out_of_range
[`File`]: https://developer.mozilla.org/en-US/docs/Web/API/File
[`JSON.stringify()`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON/stringify
[`SharedArrayBuffer`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/SharedArrayBuffer
[`String.prototype.indexOf()`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/indexOf
[`String.prototype.lastIndexOf()`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/lastIndexOf
[`String.prototype.length`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/length
[`TypedArray.from()`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray/from
[`TypedArray.prototype.set()`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray/set
[`TypedArray.prototype.slice()`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray/slice
[`TypedArray.prototype.subarray()`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray/subarray
[`TypedArray`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray
[`Uint8Array`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array
[`buf.buffer`]: #bufbuffer
[`buf.compare()`]: #bufcomparetarget-targetstart-targetend-sourcestart-sourceend
[`buf.entries()`]: #bufentries
[`buf.fill()`]: #buffillvalue-offset-end-encoding
[`buf.indexOf()`]: #bufindexofvalue-byteoffset-encoding
[`buf.keys()`]: #bufkeys
[`buf.length`]: #buflength
[`buf.slice()`]: #bufslicestart-end
[`buf.subarray`]: #bufsubarraystart-end
[`buf.toString()`]: #buftostringencoding-start-end
[`buf.values()`]: #bufvalues
[`buffer.constants.MAX_LENGTH`]: #bufferconstantsmax_length
[`buffer.constants.MAX_STRING_LENGTH`]: #bufferconstantsmax_string_length
[`buffer.kMaxLength`]: #bufferkmaxlength
[`util.inspect()`]: util.md#utilinspectobject-options
[`v8::TypedArray::kMaxLength`]: https://v8.github.io/api/head/classv8_1_1TypedArray.html#a54a48f4373da0850663c4393d843b9b0
[base64url]: https://tools.ietf.org/html/rfc4648#section-5
[endianness]: https://en.wikipedia.org/wiki/Endianness
[iterator]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols

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Code Editor : buffer.md