# Buffer

<!--introduced_in=v0.1.90-->

> Stability: 2 - Stable

Prior to the introduction of [`TypedArray`][], the JavaScript language had no
mechanism for reading or manipulating streams of binary data. The `Buffer` class
was introduced as part of the Node.js API to enable interaction with octet
streams in TCP streams, file system operations, and other contexts.

With [`TypedArray`][] now available, the `Buffer` class implements the
[`Uint8Array`][] API in a manner that is more optimized and suitable for
Node.js.

Instances of the `Buffer` class are similar to arrays of integers from `0` to
`255` (other integers are coerced to this range by `& 255` operation) but
correspond to fixed-sized, raw memory allocations outside the V8 heap.
The size of the `Buffer` is established when it is created and cannot be
changed.

The `Buffer` class is within the global scope, making it unlikely that one
would need to ever use `require('buffer').Buffer`.

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

// Creates a Buffer of length 10, filled with 0x1.
const buf2 = Buffer.alloc(10, 1);

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

// Creates a Buffer containing [0x1, 0x2, 0x3].
const buf4 = Buffer.from([1, 2, 3]);

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

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

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

In versions of Node.js prior to 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`. 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")`, it will 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 naive application 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()`][] *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
<!-- YAML
added: v5.10.0
-->

Node.js can be started using the `--zero-fill-buffers` command line option to
cause all newly allocated `Buffer` instances to be zero-filled upon creation by
default. Before Node.js 8.0.0, this included buffers allocated by `new
Buffer(size)`. Since Node.js 8.0.0, buffers allocated with `new` are always
zero-filled, whether this option is used or not.
[`Buffer.allocUnsafe()`][], [`Buffer.allocUnsafeSlow()`][], and `new
SlowBuffer(size)`. Use of this flag can have a significant negative impact on
performance. Use of the `--zero-fill-buffers` option is recommended 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.

## Buffers and Character Encodings
<!-- YAML
changes:
  - version: v6.4.0
    pr-url: https://github.com/nodejs/node/pull/7111
    description: Introduced `latin1` as an alias for `binary`.
  - version: v5.0.0
    pr-url: https://github.com/nodejs/node/pull/2859
    description: Removed the deprecated `raw` and `raws` encodings.
-->

When string data is stored in or extracted out of a `Buffer` instance, a
character encoding may be specified.

```js
const buf = Buffer.from('hello world', 'ascii');

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

console.log(Buffer.from('fhqwhgads', 'ascii'));
// 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>
```

The character encodings currently supported by Node.js include:

* `'ascii'`: For 7-bit ASCII data only. This encoding is fast and will strip
  the high bit if set.

* `'utf8'`: Multibyte encoded Unicode characters. Many web pages and other
  document formats use UTF-8.

* `'utf16le'`: 2 or 4 bytes, little-endian encoded Unicode characters.
  Surrogate pairs (U+10000 to U+10FFFF) are supported.

* `'ucs2'`: Alias of `'utf16le'`.

* `'base64'`: Base64 encoding. When creating a `Buffer` from a string,
  this encoding will also correctly accept "URL and Filename Safe Alphabet" as
  specified in [RFC 4648, Section 5][].

* `'latin1'`: A way of encoding the `Buffer` into a one-byte encoded string
  (as defined by the IANA in [RFC 1345][],
  page 63, to be the Latin-1 supplement block and C0/C1 control codes).

* `'binary'`: Alias for `'latin1'`.

* `'hex'`: Encode each byte as two hexadecimal characters.

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 TypedArray
<!-- YAML
changes:
  - version: v3.0.0
    pr-url: https://github.com/nodejs/node/pull/2002
    description: The `Buffer`s class now inherits from `Uint8Array`.
-->

`Buffer` instances are also [`Uint8Array`][] instances. However, there are
subtle incompatibilities with [`TypedArray`][]. For example, while
[`ArrayBuffer#slice()`][] creates a copy of the slice, the implementation of
[`Buffer#slice()`][`buf.slice()`] creates a view over the existing `Buffer`
without copying, making [`Buffer#slice()`][`buf.slice()`] far more efficient.

It is also possible to create new [`TypedArray`][] instances from a `Buffer`
with the following caveats:

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

2. The `Buffer` object's memory is interpreted as an array of distinct
elements, and not as a byte array of the target type. That is,
`new Uint32Array(Buffer.from([1, 2, 3, 4]))` creates a 4-element
[`Uint32Array`][] with elements `[1, 2, 3, 4]`, not a [`Uint32Array`][] with a
single element `[0x1020304]` or `[0x4030201]`.

It is possible to create a new `Buffer` that shares the same allocated memory as
a [`TypedArray`][] instance by using the `TypedArray` object's `.buffer`
property.

```js
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.

```js
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:

```js
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: Buffer

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

### new Buffer(array)
<!-- YAML
deprecated: v6.0.0
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/19524
    description: Calling this constructor emits a deprecation warning when
                 run from code outside the `node_modules` directory.
  - version: v7.2.1
    pr-url: https://github.com/nodejs/node/pull/9529
    description: Calling this constructor no longer emits a deprecation warning.
  - version: v7.0.0
    pr-url: https://github.com/nodejs/node/pull/8169
    description: Calling this constructor emits a deprecation warning now.
-->

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

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

Allocates a new `Buffer` using an `array` of octets.

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

### new Buffer(arrayBuffer\[, byteOffset\[, length\]\])
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added: v3.0.0
deprecated: v6.0.0
changes:
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    pr-url: https://github.com/nodejs/node/pull/19524
    description: Calling this constructor emits a deprecation warning when
                 run from code outside the `node_modules` directory.
  - version: v7.2.1
    pr-url: https://github.com/nodejs/node/pull/9529
    description: Calling this constructor no longer emits a deprecation warning.
  - version: v7.0.0
    pr-url: https://github.com/nodejs/node/pull/8169
    description: Calling this constructor emits a deprecation warning now.
  - version: v6.0.0
    pr-url: https://github.com/nodejs/node/pull/4682
    description: The `byteOffset` and `length` parameters are supported now.
-->

> 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.length - byteOffset`.

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

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

```js
const arr = new Uint16Array(2);

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

// Shares memory with `arr`.
const buf = new Buffer(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>
```

### new Buffer(buffer)
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deprecated: v6.0.0
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/19524
    description: Calling this constructor emits a deprecation warning when
                 run from code outside the `node_modules` directory.
  - version: v7.2.1
    pr-url: https://github.com/nodejs/node/pull/9529
    description: Calling this constructor no longer emits a deprecation warning.
  - version: v7.0.0
    pr-url: https://github.com/nodejs/node/pull/8169
    description: Calling this constructor emits a deprecation warning now.
-->

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

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

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

```js
const buf1 = new Buffer('buffer');
const buf2 = new Buffer(buf1);

buf1[0] = 0x61;

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

### new Buffer(size)
<!-- YAML
deprecated: v6.0.0
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/19524
    description: Calling this constructor emits a deprecation warning when
                 run from code outside the `node_modules` directory.
  - version: v8.0.0
    pr-url: https://github.com/nodejs/node/pull/12141
    description: The `new Buffer(size)` will return zero-filled memory by
                 default.
  - version: v7.2.1
    pr-url: https://github.com/nodejs/node/pull/9529
    description: Calling this constructor no longer emits a deprecation warning.
  - version: v7.0.0
    pr-url: https://github.com/nodejs/node/pull/8169
    description: Calling this constructor emits a deprecation warning now.
-->

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

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

Allocates a new `Buffer` of `size` bytes. If `size` is larger than
[`buffer.constants.MAX_LENGTH`][] or smaller than 0, [`ERR_INVALID_OPT_VALUE`][]
is thrown. A zero-length `Buffer` is created if `size` is 0.

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

```js
const buf = new Buffer(10);

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

### new Buffer(string\[, encoding\])
<!-- YAML
deprecated: v6.0.0
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/19524
    description: Calling this constructor emits a deprecation warning when
                 run from code outside the `node_modules` directory.
  - version: v7.2.1
    pr-url: https://github.com/nodejs/node/pull/9529
    description: Calling this constructor no longer emits a deprecation warning.
  - version: v7.0.0
    pr-url: https://github.com/nodejs/node/pull/8169
    description: Calling this constructor emits a deprecation warning now.
-->

> 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'`.

Creates a new `Buffer` containing `string`. The `encoding` parameter identifies
the character encoding of `string`.

```js
const buf1 = new Buffer('this is a tést');
const buf2 = new Buffer('7468697320697320612074c3a97374', 'hex');

console.log(buf1.toString());
// Prints: this is a tést
console.log(buf2.toString());
// Prints: this is a tést
console.log(buf1.toString('ascii'));
// Prints: this is a tC)st
```

### Class Method: Buffer.alloc(size\[, fill\[, encoding\]\])
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added: v5.10.0
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/18129
    description: Attempting to fill a non-zero length buffer with a zero length
                 buffer triggers a thrown exception.
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/17427
    description: Specifying an invalid string for `fill` triggers a thrown
                 exception.
  - version: v8.9.3
    pr-url: https://github.com/nodejs/node/pull/17428
    description: Specifying an invalid string for `fill` now results in a
                 zero-filled buffer.
-->

* `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*.

```js
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_INVALID_OPT_VALUE`][]
is thrown. A zero-length `Buffer` is created if `size` is 0.

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

```js
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()`].

```js
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 significantly slower than the alternative
[`Buffer.allocUnsafe()`][] but ensures that the newly created `Buffer` instance
contents will *never contain sensitive data*.

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

### Class Method: Buffer.allocUnsafe(size)
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added: v5.10.0
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-->

* `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_INVALID_OPT_VALUE`][]
is thrown. A zero-length `Buffer` is created if `size` is 0.

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

```js
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()`][] and the deprecated
`new Buffer(size)` constructor only when `size` is less than or equal to
`Buffer.poolSize >> 1` (floor of [`Buffer.poolSize`][] divided by two).

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

### Class Method: Buffer.allocUnsafeSlow(size)
<!-- YAML
added: v5.12.0
-->

* `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_INVALID_OPT_VALUE`][]
is thrown. A zero-length `Buffer` is created if `size` is 0.

The underlying memory for `Buffer` instances created in this way is *not
initialized*. The contents of the newly created `Buffer` are unknown and
*may contain sensitive data*. Use [`buf.fill(0)`][`buf.fill()`] to initialize
such `Buffer` instances with zeroes.

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

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

```js
// 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);
  }
});
```

`Buffer.allocUnsafeSlow()` should be used only as a last resort after a
developer has observed undue memory retention in their applications.

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

### Class Method: Buffer.byteLength(string\[, encoding\])
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added: v0.1.90
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    description: Passing invalid input will now throw an error.
  - version: v5.10.0
    pr-url: https://github.com/nodejs/node/pull/5255
    description: The `string` parameter can now be any `TypedArray`, `DataView`
                 or `ArrayBuffer`.
-->

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

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

```js
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 actual byte length is returned.

### Class Method: Buffer.compare(buf1, buf2)
<!-- YAML
added: v0.11.13
changes:
  - version: v8.0.0
    pr-url: https://github.com/nodejs/node/pull/10236
    description: The arguments can now be `Uint8Array`s.
-->

* `buf1` {Buffer|Uint8Array}
* `buf2` {Buffer|Uint8Array}
* Returns: {integer}

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

```js
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].)
```

### Class Method: Buffer.concat(list\[, totalLength\])
<!-- YAML
added: v0.7.11
changes:
  - version: v8.0.0
    pr-url: https://github.com/nodejs/node/pull/10236
    description: The elements of `list` can now be `Uint8Array`s.
-->

* `list` {Buffer[] | Uint8Array[]} List of `Buffer` or [`Uint8Array`][]
  instances to concat.
* `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`. This however causes an additional loop to be executed in order to
calculate the `totalLength`, so it is faster to provide the length explicitly if
it is already known.

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

```js
// 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
```

### Class Method: Buffer.from(array)
<!-- YAML
added: v5.10.0
-->

* `array` {integer[]}

Allocates a new `Buffer` using an `array` of octets.

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

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

### Class Method: Buffer.from(arrayBuffer\[, byteOffset\[, length\]\])
<!-- YAML
added: v5.10.0
-->

* `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.length - byteOffset`.

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

```js
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`.

```js
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 other type appropriate for `Buffer.from()` variants.

### Class Method: Buffer.from(buffer)
<!-- YAML
added: v5.10.0
-->

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

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

```js
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 other type
appropriate for `Buffer.from()` variants.

### Class Method: Buffer.from(object\[, offsetOrEncoding\[, length\]\])
<!-- YAML
added: v8.2.0
-->

* `object` {Object} An object supporting `Symbol.toPrimitive` or `valueOf()`.
* `offsetOrEncoding` {integer|string} A byte-offset or encoding, depending on
  the value returned either by `object.valueOf()` or
  `object[Symbol.toPrimitive]()`.
* `length` {integer} A length, depending on the value returned either by
  `object.valueOf()` or `object[Symbol.toPrimitive]()`.

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

```js
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](), offsetOrEncoding, length)`.

```js
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` has not mentioned methods or is not of
other type appropriate for `Buffer.from()` variants.

### Class Method: Buffer.from(string\[, encoding\])
<!-- YAML
added: v5.10.0
-->

* `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 of `string`.

```js
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('ascii'));
// Prints: this is a tC)st
```

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

### Class Method: Buffer.isBuffer(obj)
<!-- YAML
added: v0.1.101
-->

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

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

### Class Method: Buffer.isEncoding(encoding)
<!-- YAML
added: v0.9.1
-->

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

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

```js
console.log(Buffer.isEncoding('utf-8'));
// 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
<!-- YAML
added: v0.11.3
-->

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

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

### buf\[index\]
<!-- YAML
type: property
name: [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, getting returns `undefined`
and setting does nothing.

```js
// Copy an ASCII string into a `Buffer` one byte at a time.

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

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

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

### buf.buffer

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

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

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

### buf.byteOffset

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

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

This can cause problems when accessing the underlying `ArrayBuffer` directly
using `buf.buffer`, as the first bytes in this `ArrayBuffer` may be unrelated
to the `buf` object itself.

A common issue is when casting a `Buffer` object to a `TypedArray` object,
in this case one needs to specify the `byteOffset` correctly:

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

// When casting the Node.js Buffer to an Int8 TypedArray remember to use the
// byteOffset.
new Int8Array(nodeBuffer.buffer, nodeBuffer.byteOffset, nodeBuffer.length);
```

### buf.compare(target\[, targetStart\[, targetEnd\[, sourceStart\[, sourceEnd\]\]\]\])
<!-- YAML
added: v0.11.13
changes:
  - version: v8.0.0
    pr-url: https://github.com/nodejs/node/pull/10236
    description: The `target` parameter can now be a `Uint8Array`.
  - version: v5.11.0
    pr-url: https://github.com/nodejs/node/pull/5880
    description: Additional parameters for specifying offsets are supported now.
-->

* `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.

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

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

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

```js
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\[, sourceEnd\]\]\])
<!-- YAML
added: v0.1.90
-->

* `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`.

```js
// 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);

console.log(buf2.toString('ascii', 0, 25));
// Prints: !!!!!!!!qrst!!!!!!!!!!!!!
```

```js
// 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()
<!-- YAML
added: v1.1.0
-->

* Returns: {Iterator}

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

```js
// 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)
<!-- YAML
added: v0.11.13
changes:
  - version: v8.0.0
    pr-url: https://github.com/nodejs/node/pull/10236
    description: The arguments can now be `Uint8Array`s.
-->

* `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.

```js
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\[, end\]\]\[, encoding\])
<!-- YAML
added: v0.5.0
changes:
  - version: v11.0.0
    pr-url: https://github.com/nodejs/node/pull/22969
    description: Throws `ERR_OUT_OF_RANGE` instead of `ERR_INDEX_OUT_OF_RANGE`.
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/18790
    description: Negative `end` values throw an `ERR_INDEX_OUT_OF_RANGE` error.
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/18129
    description: Attempting to fill a non-zero length buffer with a zero length
                 buffer triggers a thrown exception.
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/17427
    description: Specifying an invalid string for `value` triggers a thrown
                 exception.
  - version: v5.7.0
    pr-url: https://github.com/nodejs/node/pull/4935
    description: The `encoding` parameter is supported now.
-->

* `value` {string|Buffer|Uint8Array|integer} The value with which to fill `buf`.
* `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:

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

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

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

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

```js
// Fill a `Buffer` with a two-byte character.

console.log(Buffer.allocUnsafe(3).fill('\u0222'));
// Prints: <Buffer c8 a2 c8>
```

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

```js
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\[, byteOffset\]\[, encoding\])
<!-- YAML
added: v5.3.0
-->

* `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()`].

```js
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
```

### buf.indexOf(value\[, byteOffset\]\[, encoding\])
<!-- YAML
added: v1.5.0
changes:
  - version: v8.0.0
    pr-url: https://github.com/nodejs/node/pull/10236
    description: The `value` can now be a `Uint8Array`.
  - version: v5.7.0, v4.4.0
    pr-url: https://github.com/nodejs/node/pull/4803
    description: When `encoding` is being passed, the `byteOffset` parameter
                 is no longer required.
-->

* `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.slice()`][].
* a number, `value` will be interpreted as an unsigned 8-bit integer
  value between `0` and `255`.

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

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

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

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

If `value` is not a string, number, or `Buffer`, this method will throw 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#indexOf()`][].

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

// Passing a value that's a number, but not a valid byte.
// Prints: 2, equivalent to searching for 99 or 'c'.
console.log(b.indexOf(99.9));
console.log(b.indexOf(256 + 99));

// Passing a byteOffset that coerces to NaN or 0.
// Prints: 1, searching the whole buffer.
console.log(b.indexOf('b', undefined));
console.log(b.indexOf('b', {}));
console.log(b.indexOf('b', null));
console.log(b.indexOf('b', []));
```

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

### buf.keys()
<!-- YAML
added: v1.1.0
-->

* Returns: {Iterator}

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

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

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

### buf.lastIndexOf(value\[, byteOffset\]\[, encoding\])
<!-- YAML
added: v6.0.0
changes:
  - version: v8.0.0
    pr-url: https://github.com/nodejs/node/pull/10236
    description: The `value` can now be a `Uint8Array`.
-->

* `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.

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

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

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

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

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

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

```js
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
<!-- YAML
added: v0.1.90
-->

* {integer}

Returns the amount of memory allocated for `buf` in bytes. This
does not necessarily reflect the amount of "usable" data within `buf`.

```js
// Create a `Buffer` and write a shorter ASCII string to it.

const buf = Buffer.alloc(1234);

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

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

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

While the `length` property is not immutable, changing the value of `length`
can result in undefined and inconsistent behavior. Applications that wish to
modify the length of a `Buffer` should therefore treat `length` as read-only and
use [`buf.slice()`][] to create a new `Buffer`.

```js
let buf = Buffer.allocUnsafe(10);

buf.write('abcdefghj', 0, 'ascii');

console.log(buf.length);
// Prints: 10

buf = buf.slice(0, 5);

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

### buf.parent
<!-- YAML
deprecated: v8.0.0
-->

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

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

### buf.readBigInt64BE(\[offset\])
### buf.readBigInt64LE(\[offset\])
<!-- YAML
added: v12.0.0
-->

* `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 64-bit integer from `buf` at the specified `offset` with
the specified endian format (`readBigInt64BE()` returns big endian,
`readBigInt64LE()` returns little endian).

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

### buf.readBigUInt64BE(\[offset\])
### buf.readBigUInt64LE(\[offset\])
<!-- YAML
added: v12.0.0
-->

* `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 64-bit integer from `buf` at the specified `offset` with
specified endian format (`readBigUInt64BE()` returns big endian,
`readBigUInt64LE()` returns little endian).

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

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

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

### buf.readDoubleBE(\[offset\])
### buf.readDoubleLE(\[offset\])
<!-- YAML
added: v0.11.15
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/18395
    description: Removed `noAssert` and no implicit coercion of the offset
                 to `uint32` anymore.
-->

* `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 double from `buf` at the specified `offset` with specified
endian format (`readDoubleBE()` returns big endian, `readDoubleLE()` returns
little endian).

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

console.log(buf.readDoubleBE(0));
// Prints: 8.20788039913184e-304
console.log(buf.readDoubleLE(0));
// Prints: 5.447603722011605e-270
console.log(buf.readDoubleLE(1));
// Throws ERR_OUT_OF_RANGE.
```

### buf.readFloatBE(\[offset\])
### buf.readFloatLE(\[offset\])
<!-- YAML
added: v0.11.15
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/18395
    description: Removed `noAssert` and no implicit coercion of the offset
                 to `uint32` anymore.
-->

* `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 float from `buf` at the specified `offset` with specified
endian format (`readFloatBE()` returns big endian, `readFloatLE()` returns
little endian).

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

console.log(buf.readFloatBE(0));
// Prints: 2.387939260590663e-38
console.log(buf.readFloatLE(0));
// Prints: 1.539989614439558e-36
console.log(buf.readFloatLE(1));
// Throws ERR_OUT_OF_RANGE.
```

### buf.readInt8(\[offset\])
<!-- YAML
added: v0.5.0
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/18395
    description: Removed `noAssert` and no implicit coercion of the offset
                 to `uint32` anymore.
-->

* `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.

```js
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(\[offset\])
### buf.readInt16LE(\[offset\])
<!-- YAML
added: v0.5.5
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/18395
    description: Removed `noAssert` and no implicit coercion of the offset
                 to `uint32` anymore.
-->

* `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 16-bit integer from `buf` at the specified `offset` with
the specified endian format (`readInt16BE()` returns big endian,
`readInt16LE()` returns little endian).

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

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

console.log(buf.readInt16BE(0));
// Prints: 5
console.log(buf.readInt16LE(0));
// Prints: 1280
console.log(buf.readInt16LE(1));
// Throws ERR_OUT_OF_RANGE.
```

### buf.readInt32BE(\[offset\])
### buf.readInt32LE(\[offset\])
<!-- YAML
added: v0.5.5
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/18395
    description: Removed `noAssert` and no implicit coercion of the offset
                 to `uint32` anymore.
-->

* `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 32-bit integer from `buf` at the specified `offset` with
the specified endian format (`readInt32BE()` returns big endian,
`readInt32LE()` returns little endian).

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

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

console.log(buf.readInt32BE(0));
// Prints: 5
console.log(buf.readInt32LE(0));
// Prints: 83886080
console.log(buf.readInt32LE(1));
// Throws ERR_OUT_OF_RANGE.
```

### buf.readIntBE(offset, byteLength)
### buf.readIntLE(offset, byteLength)
<!-- YAML
added: v0.11.15
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/18395
    description: Removed `noAssert` and no implicit coercion of the offset
                 and `byteLength` to `uint32` anymore.
-->

* `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 two's complement signed value. Supports up to 48
bits of accuracy.

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

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

### buf.readUInt8(\[offset\])
<!-- YAML
added: v0.5.0
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/18395
    description: Removed `noAssert` and no implicit coercion of the offset
                 to `uint32` anymore.
-->

* `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`.

```js
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(\[offset\])
### buf.readUInt16LE(\[offset\])
<!-- YAML
added: v0.5.5
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/18395
    description: Removed `noAssert` and no implicit coercion of the offset
                 to `uint32` anymore.
-->

* `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 16-bit integer from `buf` at the specified `offset` with
specified endian format (`readUInt16BE()` returns big endian, `readUInt16LE()`
returns little endian).

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

console.log(buf.readUInt16BE(0).toString(16));
// Prints: 1234
console.log(buf.readUInt16LE(0).toString(16));
// Prints: 3412
console.log(buf.readUInt16BE(1).toString(16));
// Prints: 3456
console.log(buf.readUInt16LE(1).toString(16));
// Prints: 5634
console.log(buf.readUInt16LE(2).toString(16));
// Throws ERR_OUT_OF_RANGE.
```

### buf.readUInt32BE(\[offset\])
### buf.readUInt32LE(\[offset\])
<!-- YAML
added: v0.5.5
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/18395
    description: Removed `noAssert` and no implicit coercion of the offset
                 to `uint32` anymore.
-->

* `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 32-bit integer from `buf` at the specified `offset` with
specified endian format (`readUInt32BE()` returns big endian,
`readUInt32LE()` returns little endian).

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

console.log(buf.readUInt32BE(0).toString(16));
// Prints: 12345678
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)
### buf.readUIntLE(offset, byteLength)
<!-- YAML
added: v0.11.15
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/18395
    description: Removed `noAssert` and no implicit coercion of the offset
                 and `byteLength` to `uint32` anymore.
-->

* `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 an unsigned integer. Supports up to 48
bits of accuracy.

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

console.log(buf.readUIntBE(0, 6).toString(16));
// Prints: 1234567890ab
console.log(buf.readUIntLE(0, 6).toString(16));
// Prints: ab9078563412
console.log(buf.readUIntBE(1, 6).toString(16));
// Throws ERR_OUT_OF_RANGE.
```

### buf.subarray(\[start\[, end\]\])
<!-- YAML
added: v3.0.0
-->

* `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`][].

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

```js
// 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.

```js
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\[, end\]\])
<!-- YAML
added: v0.3.0
changes:
  - version: v7.1.0, v6.9.2
    pr-url: https://github.com/nodejs/node/pull/9341
    description: Coercing the offsets to integers now handles values outside
                 the 32-bit integer range properly.
  - version: v7.0.0
    pr-url: https://github.com/nodejs/node/pull/9101
    description: All offsets are now coerced to integers before doing any
                 calculations with them.
-->

* `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.

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

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

```js
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()
<!-- YAML
added: v5.10.0
-->

* 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.

```js
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:

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

### buf.swap32()
<!-- YAML
added: v5.10.0
-->

* 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.

```js
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()
<!-- YAML
added: v6.3.0
-->

* 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.

```js
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.
```

JavaScript cannot encode 64-bit integers. This method is intended
for working with 64-bit floats.

### buf.toJSON()
<!-- YAML
added: v0.9.2
-->

* Returns: {Object}

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

```js
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.data) :
    value;
});

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

### buf.toString(\[encoding\[, start\[, end\]\]\])
<!-- YAML
added: v0.1.90
-->

* `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`.

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

```js
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('ascii'));
// Prints: abcdefghijklmnopqrstuvwxyz
console.log(buf1.toString('ascii', 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()
<!-- YAML
added: v1.1.0
-->

* 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.

```js
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\[, length\]\]\[, encoding\])
<!-- YAML
added: v0.1.90
-->

* `string` {string} String to write to `buf`.
* `offset` {integer} Number of bytes to skip before starting to write `string`.
  **Default:** `0`.
* `length` {integer} Number of bytes to write. **Default:**
  `buf.length - offset`.
* `encoding` {string} The character encoding of `string`. **Default:** `'utf8'`.
* Returns: {integer} Number of bytes written.

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

```js
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
```

### buf.writeBigInt64BE(value\[, offset\])
### buf.writeBigInt64LE(value\[, offset\])
<!-- YAML
added: v12.0.0
-->

* `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` with specified endian
format (`writeBigInt64BE()` writes big endian, `writeBigInt64LE()` writes little
endian).

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

```js
const buf = Buffer.allocUnsafe(8);

buf.writeBigInt64BE(0x0102030405060708n, 0);

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

### buf.writeBigUInt64BE(value\[, offset\])
### buf.writeBigUInt64LE(value\[, offset\])
<!-- YAML
added: v12.0.0
-->

* `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` with specified endian
format (`writeBigUInt64BE()` writes big endian, `writeBigUInt64LE()` writes
little endian).

```js
const buf = Buffer.allocUnsafe(8);

buf.writeBigUInt64LE(0xdecafafecacefaden, 0);

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

### buf.writeDoubleBE(value\[, offset\])
### buf.writeDoubleLE(value\[, offset\])
<!-- YAML
added: v0.11.15
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/18395
    description: Removed `noAssert` and no implicit coercion of the offset
                 to `uint32` anymore.
-->

* `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` with specified endian
format (`writeDoubleBE()` writes big endian, `writeDoubleLE()` writes little
endian). `value` *should* be a valid 64-bit double. Behavior is undefined when
`value` is anything other than a 64-bit double.

```js
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(123.456, 0);

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

### buf.writeFloatBE(value\[, offset\])
### buf.writeFloatLE(value\[, offset\])
<!-- YAML
added: v0.11.15
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/18395
    description: Removed `noAssert` and no implicit coercion of the offset
                 to `uint32` anymore.
-->

* `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` with specified endian
format (`writeFloatBE()` writes big endian, `writeFloatLE()` writes little
endian). `value` *should* be a valid 32-bit float. Behavior is undefined when
`value` is anything other than a 32-bit float.

```js
const buf = Buffer.allocUnsafe(4);

buf.writeFloatBE(0xcafebabe, 0);

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

buf.writeFloatLE(0xcafebabe, 0);

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

### buf.writeInt8(value\[, offset\])
<!-- YAML
added: v0.5.0
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/18395
    description: Removed `noAssert` and no implicit coercion of the offset
                 to `uint32` anymore.
-->

* `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` *should* 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.

```js
const buf = Buffer.allocUnsafe(2);

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

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

### buf.writeInt16BE(value\[, offset\])
### buf.writeInt16LE(value\[, offset\])
<!-- YAML
added: v0.5.5
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/18395
    description: Removed `noAssert` and no implicit coercion of the offset
                 to `uint32` anymore.
-->

* `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` with specified endian
format (`writeInt16BE()` writes big endian, `writeInt16LE()` writes little
endian). `value` *should* be a valid signed 16-bit integer. Behavior is
undefined when `value` is anything other than a signed 16-bit integer.

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

```js
const buf = Buffer.allocUnsafe(4);

buf.writeInt16BE(0x0102, 0);
buf.writeInt16LE(0x0304, 2);

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

### buf.writeInt32BE(value\[, offset\])
### buf.writeInt32LE(value\[, offset\])
<!-- YAML
added: v0.5.5
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/18395
    description: Removed `noAssert` and no implicit coercion of the offset
                 to `uint32` anymore.
-->

* `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` with specified endian
format (`writeInt32BE()` writes big endian, `writeInt32LE()` writes little
endian). `value` *should* be a valid signed 32-bit integer. Behavior is
undefined when `value` is anything other than a signed 32-bit integer.

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

```js
const buf = Buffer.allocUnsafe(8);

buf.writeInt32BE(0x01020304, 0);
buf.writeInt32LE(0x05060708, 4);

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

### buf.writeIntBE(value, offset, byteLength)
### buf.writeIntLE(value, offset, byteLength)
<!-- YAML
added: v0.11.15
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/18395
    description: Removed `noAssert` and no implicit coercion of the offset
                 and `byteLength` to `uint32` anymore.
-->

* `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`.
Supports up to 48 bits of accuracy. Behavior is undefined when `value` is
anything other than a signed integer.

```js
const buf = Buffer.allocUnsafe(6);

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

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

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

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

### buf.writeUInt8(value\[, offset\])
<!-- YAML
added: v0.5.0
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/18395
    description: Removed `noAssert` and no implicit coercion of the offset
                 to `uint32` anymore.
-->

* `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` *should* be a
valid unsigned 8-bit integer. Behavior is undefined when `value` is anything
other than an unsigned 8-bit integer.

```js
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\[, offset\])
### buf.writeUInt16LE(value\[, offset\])
<!-- YAML
added: v0.5.5
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/18395
    description: Removed `noAssert` and no implicit coercion of the offset
                 to `uint32` anymore.
-->

* `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` with specified endian
format (`writeUInt16BE()` writes big endian, `writeUInt16LE()` writes little
endian). `value` should be a valid unsigned 16-bit integer. Behavior is
undefined when `value` is anything other than an unsigned 16-bit integer.

```js
const buf = Buffer.allocUnsafe(4);

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

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

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

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

### buf.writeUInt32BE(value\[, offset\])
### buf.writeUInt32LE(value\[, offset\])
<!-- YAML
added: v0.5.5
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/18395
    description: Removed `noAssert` and no implicit coercion of the offset
                 to `uint32` anymore.
-->

* `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` with specified endian
format (`writeUInt32BE()` writes big endian, `writeUInt32LE()` writes little
endian). `value` should be a valid unsigned 32-bit integer. Behavior is
undefined when `value` is anything other than an unsigned 32-bit integer.

```js
const buf = Buffer.allocUnsafe(4);

buf.writeUInt32BE(0xfeedface, 0);

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

buf.writeUInt32LE(0xfeedface, 0);

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

### buf.writeUIntBE(value, offset, byteLength)
### buf.writeUIntLE(value, offset, byteLength)
<!-- YAML
added: v0.5.5
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/18395
    description: Removed `noAssert` and no implicit coercion of the offset
                 and `byteLength` to `uint32` anymore.
-->

* `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`.
Supports up to 48 bits of accuracy. Behavior is undefined when `value` is
anything other than an unsigned integer.

```js
const buf = Buffer.allocUnsafe(6);

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

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

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

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

## buffer.INSPECT_MAX_BYTES
<!-- YAML
added: v0.5.4
-->

* {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.

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

## buffer.kMaxLength
<!-- YAML
added: v3.0.0
-->

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

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

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

## buffer.transcode(source, fromEnc, toEnc)
<!-- YAML
added: v7.1.0
changes:
  - version: v8.0.0
    pr-url: https://github.com/nodejs/node/pull/10236
    description: The `source` parameter can now be a `Uint8Array`.
-->

* `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:

```js
const buffer = require('buffer');

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

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

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

## Class: SlowBuffer
<!-- YAML
deprecated: v6.0.0
-->

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

Returns an un-pooled `Buffer`.

In order to avoid the garbage collection overhead of creating many individually
allocated `Buffer` instances, by default allocations under 4KB are sliced from a
single larger allocated object.

In the case where a developer may need to retain a small chunk of memory from a
pool for an indeterminate amount of time, it may be appropriate to create an
un-pooled `Buffer` instance using `SlowBuffer` then copy out the relevant bits.

```js
// 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 = SlowBuffer(10);

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

    store.push(sb);
  }
});
```

Use of `SlowBuffer` should be used only as a last resort *after* a developer
has observed undue memory retention in their applications.

### new SlowBuffer(size)
<!-- YAML
deprecated: v6.0.0
-->

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

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

Allocates a new `Buffer` of `size` bytes. If `size` is larger than
[`buffer.constants.MAX_LENGTH`][] or smaller than 0, [`ERR_INVALID_OPT_VALUE`][]
is thrown. A zero-length `Buffer` is created if `size` is 0.

The underlying memory for `SlowBuffer` instances is *not initialized*. The
contents of a newly created `SlowBuffer` are unknown and may contain sensitive
data. Use [`buf.fill(0)`][`buf.fill()`] to initialize a `SlowBuffer` with
zeroes.

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

const buf = new SlowBuffer(5);

console.log(buf);
// Prints: (contents may vary): <Buffer 78 e0 82 02 01>

buf.fill(0);

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

## Buffer Constants
<!-- YAML
added: v8.2.0
-->

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

### buffer.constants.MAX_LENGTH
<!-- YAML
added: v8.2.0
-->

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

On 32-bit architectures, this value is `(2^30)-1` (~1GB).
On 64-bit architectures, this value is `(2^31)-1` (~2GB).

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

### buffer.constants.MAX_STRING_LENGTH
<!-- YAML
added: v8.2.0
-->

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

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

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

[RFC 1345]: https://tools.ietf.org/html/rfc1345
[RFC 4648, Section 5]: https://tools.ietf.org/html/rfc4648#section-5
[WHATWG Encoding Standard]: https://encoding.spec.whatwg.org/
[`ArrayBuffer#slice()`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer/slice
[`ArrayBuffer`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer
[`Buffer.alloc()`]: #buffer_class_method_buffer_alloc_size_fill_encoding
[`Buffer.allocUnsafe()`]: #buffer_class_method_buffer_allocunsafe_size
[`Buffer.allocUnsafeSlow()`]: #buffer_class_method_buffer_allocunsafeslow_size
[`Buffer.from(array)`]: #buffer_class_method_buffer_from_array
[`Buffer.from(arrayBuf)`]: #buffer_class_method_buffer_from_arraybuffer_byteoffset_length
[`Buffer.from(buffer)`]: #buffer_class_method_buffer_from_buffer
[`Buffer.from(string)`]: #buffer_class_method_buffer_from_string_encoding
[`Buffer.poolSize`]: #buffer_class_property_buffer_poolsize
[`DataView`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView
[`ERR_INVALID_BUFFER_SIZE`]: errors.html#ERR_INVALID_BUFFER_SIZE
[`ERR_INVALID_OPT_VALUE`]: errors.html#ERR_INVALID_OPT_VALUE
[`ERR_OUT_OF_RANGE`]: errors.html#ERR_OUT_OF_RANGE
[`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#indexOf()`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/indexOf
[`String#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`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray
[`Uint32Array`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint32Array
[`Uint8Array`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array
[`buf.buffer`]: #buffer_buf_buffer
[`buf.compare()`]: #buffer_buf_compare_target_targetstart_targetend_sourcestart_sourceend
[`buf.entries()`]: #buffer_buf_entries
[`buf.fill()`]: #buffer_buf_fill_value_offset_end_encoding
[`buf.indexOf()`]: #buffer_buf_indexof_value_byteoffset_encoding
[`buf.keys()`]: #buffer_buf_keys
[`buf.length`]: #buffer_buf_length
[`buf.slice()`]: #buffer_buf_slice_start_end
[`buf.values()`]: #buffer_buf_values
[`buffer.constants.MAX_LENGTH`]: #buffer_buffer_constants_max_length
[`buffer.constants.MAX_STRING_LENGTH`]: #buffer_buffer_constants_max_string_length
[`buffer.kMaxLength`]: #buffer_buffer_kmaxlength
[`util.inspect()`]: util.html#util_util_inspect_object_options
[iterator]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols
