# 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 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`. Starting in Node.js 8.0.0, `Buffer(num)` and
  `new Buffer(num)` will return a `Buffer` with initialized memory.
* Passing a string, array, or `Buffer` as the first argument copies the
  passed object's data into the `Buffer`.
* Passing an [`ArrayBuffer`] 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.

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.
* [`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, including buffers returned by `new Buffer(size)`,
[`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.

```txt
$ 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>
```

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

```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]);

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

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

## Class: Buffer

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

### new Buffer(array)
<!-- 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]])
<!-- YAML
added: v3.0.0
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.
  - 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)
<!-- 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(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]])
<!-- YAML
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|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>
```

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.

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
changes:
  - version: v7.0.0
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    description: Passing a negative `size` will now throw an error.
-->

* `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.

Note that the `Buffer` module pre-allocates an internal `Buffer` instance of
size [`Buffer.poolSize`] that is used as a pool for the fast allocation of new
`Buffer` instances created using [`Buffer.allocUnsafe()`] and the deprecated
`new Buffer(size)` constructor only when `size` is less than or equal to
`Buffer.poolSize >> 1` (floor of [`Buffer.poolSize`] divided by two).

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

### Class Method: Buffer.allocUnsafeSlow(size)
<!-- 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])
<!-- YAML
added: v0.1.90
changes:
  - version: v7.0.0
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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`.

### 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`].

### 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`.

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

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

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

```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>
```

### 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.

### 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.

### 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]
-->

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

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

```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 with `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} 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|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|integer} What to search for.
* `byteOffset` {integer} Where to begin searching in `buf`. **Default:** `0`.
* `encoding` {string} If `value` is a string, this is its encoding.
  **Default:** `'utf8'`.
* Returns: {boolean} `true` if `value` was found in `buf`, `false` otherwise.

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

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

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

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

### 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
```

Note that 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.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`.
* 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`.
* 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`.
* 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`.
* 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`.
* 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`.
* 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`.
* 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`.
* 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.

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

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

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

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

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

## buffer.transcode(source, fromEnc, toEnc)
<!-- 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.

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`.

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

## Class: SlowBuffer
<!-- 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
-->

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

### buffer.constants.MAX_LENGTH
<!-- 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
