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# Buffer#

Stability: 2 - Stable

Prior to the introduction of `TypedArray` in ECMAScript 2015 (ES6), 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 make it possible to interact with octet streams in the context of things like TCP streams and file system operations.

Now that `TypedArray` has been added in ES6, the `Buffer` class implements the `Uint8Array` API in a manner that is more optimized and suitable for Node.js' use cases.

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 resized.

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

Examples:

    // 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 v6, `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)` or by writing to the `Buffer` completely. 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` returns a `Buffer` that shares allocated memory with the given `ArrayBuffer`.

Because the behavior of `new Buffer()` changes significantly based on the type of value passed as the first argument, applications that do not properly validate the input arguments passed to `new Buffer()`, or that fail to appropriately initialize newly allocated `Buffer` content, can inadvertently introduce security and reliability issues into their code.

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` containing a copy of the provided octets.
- `Buffer.from(arrayBuffer[, byteOffset [, length]])` returns a new `Buffer` that shares the same allocated memory as the given `ArrayBuffer`.
- `Buffer.from(buffer)` returns a new `Buffer` containing a copy of the contents of the given `Buffer`.
- `Buffer.from(string[, encoding])` returns a new `Buffer` containing a copy of the provided string.
- `Buffer.alloc(size[, fill[, encoding]])` returns a "filled" `Buffer` instance of the specified size. This method can be significantly slower than `Buffer.allocUnsafe(size)` but ensures that newly created `Buffer` instances never contain old and potentially sensitive data.
- `Buffer.allocUnsafe(size)` and `Buffer.allocUnsafeSlow(size)` each return a new `Buffer` of the specified `size` whose content must be initialized using either `buf.fill(0)` or written to completely.

`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#

Added in: v5.10.0

Node.js can be started using the `--zero-fill-buffers` command line option to force all newly allocated `Buffer` instances created using either `new Buffer(size)`, `Buffer.allocUnsafe()`, `Buffer.allocUnsafeSlow()` or `new SlowBuffer(size)` to be automatically zero-filled upon creation. Use of this flag changes the default behavior of these methods and can have a significant impact on performance. Use of the `--zero-fill-buffers` option is recommended only when necessary to enforce that newly allocated `Buffer` instances cannot contain potentially sensitive data.

Example:

    $ 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#

History

Version | Changes
--- | ---
v6.4.0 | Introduced `latin1` as an alias for `binary`.
v5.0.0 | Removed the deprecated `raw` and `raws` encodings.

`Buffer` instances are commonly used to represent sequences of encoded characters such as UTF-8, UCS2, Base64 or even Hex-encoded data. It is possible to convert back and forth between `Buffer` instances and ordinary JavaScript strings by using an explicit character encoding.

Example:

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

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

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

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 RFC4648, Section 5.

- `'latin1'` - A way of encoding the `Buffer` into a one-byte encoded string (as defined by the IANA in RFC1345, 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.

Note: Today's 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#

History

Version | Changes
--- | ---
v3.0.0 | The `Buffer`s class now inherits from `Uint8Array`.

`Buffer` instances are also `Uint8Array` instances. However, there are subtle incompatibilities with the TypedArray specification in ECMAScript 2015. For example, while `ArrayBuffer#slice()` creates a copy of the slice, the implementation of `Buffer#slice()` creates a view over the existing `Buffer` without copying, making `Buffer#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 TypeArray object's `.buffer` property.

Example:

    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);

    // Prints: <Buffer 88 a0>
    console.log(buf1);

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

    arr[1] = 6000;

    // Prints: <Buffer 88 a0>
    console.log(buf1);

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

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.

Example:

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

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

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

- `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(string[, encoding])`

## Buffers and ES6 iteration#

`Buffer` instances can be iterated over using the ECMAScript 2015 (ES6) `for..of` syntax.

Example:

    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)#

History

Version | Changes
--- | ---
v7.2.1 | Calling this constructor no longer emits a deprecation warning.
v7.0.0 | Calling this constructor emits a deprecation warning now.
v6.0.0 | Deprecated since: v6.0.0

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.

Example:

    // 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]])#

History

Version | Changes
--- | ---
v7.2.1 | Calling this constructor no longer emits a deprecation warning.
v7.0.0 | Calling this constructor emits a deprecation warning now.
v6.0.0 | The `byteOffset` and `length` parameters are supported now.
v6.0.0 | Deprecated since: v6.0.0
v3.0.0 | Added in: v3.0.0

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

- `arrayBuffer` <ArrayBuffer> An `ArrayBuffer` 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`.

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

Example:

    const arr = new Uint16Array(2);

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

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

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

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

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

### new Buffer(buffer)#

History

Version | Changes
--- | ---
v7.2.1 | Calling this constructor no longer emits a deprecation warning.
v7.0.0 | Calling this constructor emits a deprecation warning now.
v6.0.0 | Deprecated since: v6.0.0

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

- `buffer` <Buffer> An existing `Buffer` to copy data from.

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

Example:

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

    buf1[0] = 0x61;

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

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

### new Buffer(size)#

History

Version | Changes
--- | ---
v8.0.0 | new Buffer(size) will return zero-filled memory by default.
v7.2.1 | Calling this constructor no longer emits a deprecation warning.
v7.0.0 | Calling this constructor emits a deprecation warning now.
v6.0.0 | Deprecated since: v6.0.0

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 the `size` is larger than `buffer.constants.MAX_LENGTH` or smaller than 0, a `RangeError` will be thrown. A zero-length `Buffer` will be 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)` instead to initialize a `Buffer` to zeroes.

Example:

    const buf = new Buffer(10);

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

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

History

Version | Changes
--- | ---
v7.2.1 | Calling this constructor no longer emits a deprecation warning.
v7.0.0 | Calling this constructor emits a deprecation warning now.
v6.0.0 | Deprecated since: v6.0.0

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

- `string` <string> String to encode.
- `encoding` <string> The encoding of `string`. Default: `'utf8'`

Creates a new `Buffer` containing the given JavaScript string `string`. If provided, the `encoding` parameter identifies the character encoding of `string`.

Examples:

    const buf1 = new Buffer('this is a tést');

    // Prints: this is a tést
    console.log(buf1.toString());

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

    const buf2 = new Buffer('7468697320697320612074c3a97374', 'hex');

    // Prints: this is a tést
    console.log(buf2.toString());

### Class Method: Buffer.alloc(size[, fill[, encoding]])#

Added in: v5.10.0

- `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.

Example:

    const buf = Buffer.alloc(5);

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

Allocates a new `Buffer` of `size` bytes. If the `size` is larger than `buffer.constants.MAX_LENGTH` or smaller than 0, a `RangeError` will be thrown. A zero-length `Buffer` will be created if `size` is 0.

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

Example:

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

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

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

Example:

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

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

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)#

History

Version | Changes
--- | ---
v7.0.0 | Passing a negative `size` will now throw an error.
v5.10.0 | Added in: v5.10.0

- `size` <integer> The desired length of the new `Buffer`.

Allocates a new `Buffer` of `size` bytes. If the `size` is larger than `buffer.constants.MAX_LENGTH` or smaller than 0, a `RangeError` will be thrown. A zero-length `Buffer` will be 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 to zeroes.

Example:

    const buf = Buffer.allocUnsafe(10);

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

    buf.fill(0);

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

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)#

Added in: v5.12.0

- `size` <integer> The desired length of the new `Buffer`.

Allocates a new `Buffer` of `size` bytes. If the `size` is larger than `buffer.constants.MAX_LENGTH` or smaller than 0, a `RangeError` will be thrown. A zero-length `Buffer` will be created if `size` is 0.

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

When using `Buffer.allocUnsafe()` to allocate new `Buffer` instances, allocations under 4KB are, by default, 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 cleanup 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()` then copy out the relevant bits.

Example:

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

    socket.on('readable', () => {
      const data = socket.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);
    });

Use of `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])#

History

Version | Changes
--- | ---
v7.0.0 | Passing invalid input will now throw an error.
v5.10.0 | The `string` parameter can now be any `TypedArray`, `DataView` or `ArrayBuffer`.
v0.1.90 | Added in: v0.1.90

- `string` <string> | <Buffer> | <TypedArray> | <DataView> | <ArrayBuffer> 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.

Note: 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.

Example:

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

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

When `string` is a `Buffer`/`DataView`/`TypedArray`/`ArrayBuffer`, the actual byte length is returned.

### Class Method: Buffer.compare(buf1, buf2)#

History

Version | Changes
--- | ---
v8.0.0 | The arguments can now be `Uint8Array`s.
v0.11.13 | Added in: v0.11.13

- `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)`.

Example:

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

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

### Class Method: Buffer.concat(list[, totalLength])#

History

Version | Changes
--- | ---
v8.0.0 | The elements of `list` can now be `Uint8Array`s.
v0.7.11 | Added in: v0.7.11

- `list` <Array> 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`.

Example: 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;

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

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

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

    // Prints: 42
    console.log(bufA.length);

### Class Method: Buffer.from(array)#

Added in: v5.10.0

- `array` <Array>

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

Example:

    // 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]])#

Added in: v5.10.0

- `arrayBuffer` <ArrayBuffer> An `ArrayBuffer` 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`.

Example:

    const arr = new Uint16Array(2);

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

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

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

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

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

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

Example:

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

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

A `TypeError` will be thrown if `arrayBuffer` is not an `ArrayBuffer`.

### Class Method: Buffer.from(buffer)#

Added in: v5.10.0

- `buffer` <Buffer> An existing `Buffer` to copy data from.

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

Example:

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

    buf1[0] = 0x61;

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

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

A `TypeError` will be thrown if `buffer` is not a `Buffer`.

### Class Method: Buffer.from(string[, encoding])#

Added in: v5.10.0

- `string` <string> A string to encode.
- `encoding` <string> The encoding of `string`. Default: `'utf8'`

Creates a new `Buffer` containing the given JavaScript string `string`. If provided, the `encoding` parameter identifies the character encoding of `string`.

Examples:

    const buf1 = Buffer.from('this is a tést');

    // Prints: this is a tést
    console.log(buf1.toString());

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

    const buf2 = Buffer.from('7468697320697320612074c3a97374', 'hex');

    // Prints: this is a tést
    console.log(buf2.toString());

A `TypeError` will be thrown if `string` is not a string.

### Class Method: Buffer.from(object[, offsetOrEncoding[, length]])#

Added in: 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)`.

For example:

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

For example:

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

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

### Class Method: Buffer.isBuffer(obj)#

Added in: v0.1.101

- `obj` <Object>
- Returns: <boolean>

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

### Class Method: Buffer.isEncoding(encoding)#

Added in: 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#

Added in: v0.11.3

- <integer> Default: `8192`

This is the number of bytes used to determine the size of pre-allocated, internal `Buffer` instances used for pooling. This value may be modified.

### buf[index]#

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

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

Example: 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);
    }

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

### buf.buffer#

The `buffer` property references the underlying `ArrayBuffer` object based on which this Buffer object is created.

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

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

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

History

Version | Changes
--- | ---
v8.0.0 | The `target` parameter can now be a `Uint8Array`.
v5.11.0 | Additional parameters for specifying offsets are supported now.
v0.11.13 | Added in: v0.11.13

- `target` <Buffer> | <Uint8Array> A `Buffer` or `Uint8Array` to compare to.
- `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). Ignored when `targetStart` is `undefined`. Default: `target.length`
- `sourceStart` <integer> The offset within `buf` at which to begin comparison. Ignored when `targetStart` is `undefined`. Default: `0`
- `sourceEnd` <integer> The offset within `buf` at which to end comparison (not inclusive). Ignored when `targetStart` is `undefined`. 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.

Examples:

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

    // Prints: 0
    console.log(buf1.compare(buf1));

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

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

Examples:

    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]);

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

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

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

A `RangeError` will be thrown if: `targetStart < 0`, `sourceStart < 0`, `targetEnd > target.byteLength` or `sourceEnd > source.byteLength`.

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

Added in: v0.1.90

- `target` <Buffer> | <Uint8Array> A `Buffer` or `Uint8Array` to copy into.
- `targetStart` <integer> The offset within `target` at which to begin copying to. Default: `0`
- `sourceStart` <integer> The offset within `buf` at which to begin copying from. Ignored when `targetStart` is `undefined`. Default: `0`
- `sourceEnd` <integer> The offset within `buf` at which to stop copying (not inclusive). Ignored when `sourceStart` is `undefined`. 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`.

Example: Create two `Buffer` instances, `buf1` and `buf2`, and copy `buf1` from byte 16 through byte 19 into `buf2`, starting at the 8th byte in `buf2`

    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;
    }

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

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

Example: Create a single `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);

    // Prints: efghijghijklmnopqrstuvwxyz
    console.log(buf.toString());

### buf.entries()#

Added in: v1.1.0

- Returns: <Iterator>

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

Example: Log the entire contents of a `Buffer`

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

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

### buf.equals(otherBuffer)#

History

Version | Changes
--- | ---
v8.0.0 | The arguments can now be `Uint8Array`s.
v0.11.13 | Added in: v0.11.13

- `otherBuffer` <Buffer> A `Buffer` or `Uint8Array` to compare to.
- Returns: <boolean>

Returns `true` if both `buf` and `otherBuffer` have exactly the same bytes, `false` otherwise.

Examples:

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

    // Prints: true
    console.log(buf1.equals(buf2));

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

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

History

Version | Changes
--- | ---
v5.7.0 | The `encoding` parameter is supported now.
v0.5.0 | Added in: v0.5.0

- `value` <string> | <Buffer> | <integer> The value to fill `buf` with.
- `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> If `value` is a string, this is its encoding. 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. This is meant to be a small simplification to allow the creation and filling of a `Buffer` to be done on a single line.

Example: Fill a `Buffer` with the ASCII character `'h'`

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

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

`value` is coerced to a `uint32` value if it is not a String or Integer.

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

Example: Fill a `Buffer` with a two-byte character

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

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

Added in: 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`.

Examples:

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

    // Prints: true
    console.log(buf.includes('this'));

    // Prints: true
    console.log(buf.includes('is'));

    // Prints: true
    console.log(buf.includes(Buffer.from('a buffer')));

    // Prints: true
    // (97 is the decimal ASCII value for 'a')
    console.log(buf.includes(97));

    // Prints: false
    console.log(buf.includes(Buffer.from('a buffer example')));

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

    // Prints: false
    console.log(buf.includes('this', 4));

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

History

Version | Changes
--- | ---
v8.0.0 | The `value` can now be a `Uint8Array`.
v5.7.0, v4.4.0 | When `encoding` is being passed, the `byteOffset` parameter is no longer required.
v1.5.0 | Added in: v1.5.0

- `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 its encoding. 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`.

Examples:

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

    // Prints: 0
    console.log(buf.indexOf('this'));

    // Prints: 2
    console.log(buf.indexOf('is'));

    // Prints: 8
    console.log(buf.indexOf(Buffer.from('a buffer')));

    // Prints: 8
    // (97 is the decimal ASCII value for 'a')
    console.log(buf.indexOf(97));

    // Prints: -1
    console.log(buf.indexOf(Buffer.from('a buffer example')));

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

    const utf16Buffer = Buffer.from('\u039a\u0391\u03a3\u03a3\u0395', 'ucs2');

    // Prints: 4
    console.log(utf16Buffer.indexOf('\u03a3', 0, 'ucs2'));

    // Prints: 6
    console.log(utf16Buffer.indexOf('\u03a3', -4, 'ucs2'));

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` or 0, like `{}`, `[]`, `null` or `undefined`, will search the whole buffer. This behavior matches `String#indexOf()`.

    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()#

Added in: v1.1.0

- Returns: <Iterator>

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

Example:

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

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

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

History

Version | Changes
--- | ---
v8.0.0 | The `value` can now be a `Uint8Array`.
v6.0.0 | Added in: v6.0.0

- `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 its encoding. 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 `buf` is searched from back to front instead of front to back.

Examples:

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

    // Prints: 0
    console.log(buf.lastIndexOf('this'));

    // Prints: 17
    console.log(buf.lastIndexOf('buffer'));

    // Prints: 17
    console.log(buf.lastIndexOf(Buffer.from('buffer')));

    // Prints: 15
    // (97 is the decimal ASCII value for 'a')
    console.log(buf.lastIndexOf(97));

    // Prints: -1
    console.log(buf.lastIndexOf(Buffer.from('yolo')));

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

    // Prints: -1
    console.log(buf.lastIndexOf('buffer', 4));

    const utf16Buffer = Buffer.from('\u039a\u0391\u03a3\u03a3\u0395', 'ucs2');

    // Prints: 6
    console.log(utf16Buffer.lastIndexOf('\u03a3', undefined, 'ucs2'));

    // Prints: 4
    console.log(utf16Buffer.lastIndexOf('\u03a3', -5, 'ucs2'));

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()`.

    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#

Added in: 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`.

Example: Create a `Buffer` and write a shorter ASCII string to it

    const buf = Buffer.alloc(1234);

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

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

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

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`.

Examples:

    let buf = Buffer.allocUnsafe(10);

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

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

    buf = buf.slice(0, 5);

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

### buf.parent#

Deprecated since: v8.0.0
Stability: 0 - Deprecated: Use `buf.buffer` instead.

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

### buf.readDoubleBE(offset[, noAssert])#

### buf.readDoubleLE(offset[, noAssert])#

Added in: v0.11.15

- `offset` <integer> Number of bytes to skip before starting to read. Must satisfy: `0 <= offset <= buf.length - 8`.
- `noAssert` <boolean> Skip `offset` validation? Default: `false`
- 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).

Setting `noAssert` to `true` allows `offset` to be beyond the end of `buf`, but the result should be considered undefined behavior.

Examples:

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

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

    // Prints: 5.447603722011605e-270
    console.log(buf.readDoubleLE());

    // Throws an exception: RangeError: Index out of range
    console.log(buf.readDoubleLE(1));

    // Warning: reads passed end of buffer!
    // This will result in a segmentation fault! Don't do this!
    console.log(buf.readDoubleLE(1, true));

### buf.readFloatBE(offset[, noAssert])#

### buf.readFloatLE(offset[, noAssert])#

Added in: v0.11.15

- `offset` <integer> Number of bytes to skip before starting to read. Must satisfy: `0 <= offset <= buf.length - 4`.
- `noAssert` <boolean> Skip `offset` validation? Default: `false`
- 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).

Setting `noAssert` to `true` allows `offset` to be beyond the end of `buf`, but the result should be considered undefined behavior.

Examples:

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

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

    // Prints: 1.539989614439558e-36
    console.log(buf.readFloatLE());

    // Throws an exception: RangeError: Index out of range
    console.log(buf.readFloatLE(1));

    // Warning: reads passed end of buffer!
    // This will result in a segmentation fault! Don't do this!
    console.log(buf.readFloatLE(1, true));

### buf.readInt8(offset[, noAssert])#

Added in: v0.5.0

- `offset` <integer> Number of bytes to skip before starting to read. Must satisfy: `0 <= offset <= buf.length - 1`.
- `noAssert` <boolean> Skip `offset` validation? Default: `false`
- Returns: <integer>

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

Setting `noAssert` to `true` allows `offset` to be beyond the end of `buf`, but the result should be considered undefined behavior.

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

Examples:

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

    // Prints: -1
    console.log(buf.readInt8(0));

    // Prints: 5
    console.log(buf.readInt8(1));

    // Throws an exception: RangeError: Index out of range
    console.log(buf.readInt8(2));

### buf.readInt16BE(offset[, noAssert])#

### buf.readInt16LE(offset[, noAssert])#

Added in: v0.5.5

- `offset` <integer> Number of bytes to skip before starting to read. Must satisfy: `0 <= offset <= buf.length - 2`.
- `noAssert` <boolean> Skip `offset` validation? Default: `false`
- 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).

Setting `noAssert` to `true` allows `offset` to be beyond the end of `buf`, but the result should be considered undefined behavior.

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

Examples:

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

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

    // Prints: 1280
    console.log(buf.readInt16LE());

    // Throws an exception: RangeError: Index out of range
    console.log(buf.readInt16LE(1));

### buf.readInt32BE(offset[, noAssert])#

### buf.readInt32LE(offset[, noAssert])#

Added in: v0.5.5

- `offset` <integer> Number of bytes to skip before starting to read. Must satisfy: `0 <= offset <= buf.length - 4`.
- `noAssert` <boolean> Skip `offset` validation? Default: `false`
- 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).

Setting `noAssert` to `true` allows `offset` to be beyond the end of `buf`, but the result should be considered undefined behavior.

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

Examples:

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

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

    // Prints: 83886080
    console.log(buf.readInt32LE());

    // Throws an exception: RangeError: Index out of range
    console.log(buf.readInt32LE(1));

### buf.readIntBE(offset, byteLength[, noAssert])#

### buf.readIntLE(offset, byteLength[, noAssert])#

Added in: v0.11.15

- `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`.
- `noAssert` <boolean> Skip `offset` and `byteLength` validation? Default: `false`.
- 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.

Setting `noAssert` to `true` allows `offset` to be beyond the end of `buf`, but the result should be considered undefined behavior.

Examples:

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

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

    // Prints: 1234567890ab
    console.log(buf.readIntBE(0, 6).toString(16));

    // Throws an exception: RangeError: Index out of range
    console.log(buf.readIntBE(1, 6).toString(16));

### buf.readUInt8(offset[, noAssert])#

Added in: v0.5.0

- `offset` <integer> Number of bytes to skip before starting to read. Must satisfy: `0 <= offset <= buf.length - 1`.
- `noAssert` <boolean> Skip `offset` validation? Default: `false`
- Returns: <integer>

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

Setting `noAssert` to `true` allows `offset` to be beyond the end of `buf`, but the result should be considered undefined behavior.

Examples:

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

    // Prints: 1
    console.log(buf.readUInt8(0));

    // Prints: 254
    console.log(buf.readUInt8(1));

    // Throws an exception: RangeError: Index out of range
    console.log(buf.readUInt8(2));

### buf.readUInt16BE(offset[, noAssert])#

### buf.readUInt16LE(offset[, noAssert])#

Added in: v0.5.5

- `offset` <integer> Number of bytes to skip before starting to read. Must satisfy: `0 <= offset <= buf.length - 2`.
- `noAssert` <boolean> Skip `offset` validation? Default: `false`
- 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).

Setting `noAssert` to `true` allows `offset` to be beyond the end of `buf`, but the result should be considered undefined behavior.

Examples:

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

    // Prints: 1234
    console.log(buf.readUInt16BE(0).toString(16));

    // Prints: 3412
    console.log(buf.readUInt16LE(0).toString(16));

    // Prints: 3456
    console.log(buf.readUInt16BE(1).toString(16));

    // Prints: 5634
    console.log(buf.readUInt16LE(1).toString(16));

    // Throws an exception: RangeError: Index out of range
    console.log(buf.readUInt16LE(2).toString(16));

### buf.readUInt32BE(offset[, noAssert])#

### buf.readUInt32LE(offset[, noAssert])#

Added in: v0.5.5

- `offset` <integer> Number of bytes to skip before starting to read. Must satisfy: `0 <= offset <= buf.length - 4`.
- `noAssert` <boolean> Skip `offset` validation? Default: `false`
- 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).

Setting `noAssert` to `true` allows `offset` to be beyond the end of `buf`, but the result should be considered undefined behavior.

Examples:

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

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

    // Prints: 78563412
    console.log(buf.readUInt32LE(0).toString(16));

    // Throws an exception: RangeError: Index out of range
    console.log(buf.readUInt32LE(1).toString(16));

### buf.readUIntBE(offset, byteLength[, noAssert])#

### buf.readUIntLE(offset, byteLength[, noAssert])#

Added in: v0.11.15

- `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`.
- `noAssert` <boolean> Skip `offset` and `byteLength` validation? Default: `false`
- 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.

Setting `noAssert` to `true` allows `offset` to be beyond the end of `buf`, but the result should be considered undefined behavior.

Examples:

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

    // Prints: 1234567890ab
    console.log(buf.readUIntBE(0, 6).toString(16));

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

    // Throws an exception: RangeError: Index out of range
    console.log(buf.readUIntBE(1, 6).toString(16));

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

History

Version | Changes
--- | ---
v7.1.0, v6.9.2 | Coercing the offsets to integers now handles values outside the 32-bit integer range properly.
v7.0.0 | All offsets are now coerced to integers before doing any calculations with them.
v0.3.0 | Added in: v0.3.0

- `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`.

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

Example: Create a `Buffer` with the ASCII alphabet, take a slice, and then 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);

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

    buf1[0] = 33;

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

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

Examples:

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

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

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

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

### buf.swap16()#

Added in: 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 a `RangeError` if `buf.length` is not a multiple of 2.

Examples:

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

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

    buf1.swap16();

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

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

    // Throws an exception: RangeError: Buffer size must be a multiple of 16-bits
    buf2.swap16();

### buf.swap32()#

Added in: 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 a `RangeError` if `buf.length` is not a multiple of 4.

Examples:

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

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

    buf1.swap32();

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

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

    // Throws an exception: RangeError: Buffer size must be a multiple of 32-bits
    buf2.swap32();

### buf.swap64()#

Added in: v6.3.0

- Returns: <Buffer> A reference to `buf`.

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

Examples:

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

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

    buf1.swap64();

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

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

    // Throws an exception: RangeError: Buffer size must be a multiple of 64-bits
    buf2.swap64();

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

### buf.toJSON()#

Added in: v0.9.2

- Returns: <Object>

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

Example:

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

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

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

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

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

Added in: v0.1.90

- `encoding` <string> The character encoding to decode to. 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`.

Examples:

    const buf1 = Buffer.allocUnsafe(26);

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

    // Prints: abcdefghijklmnopqrstuvwxyz
    console.log(buf1.toString('ascii'));

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

    const buf2 = Buffer.from('tést');

    // Prints: 74c3a97374
    console.log(buf2.toString('hex'));

    // Prints: té
    console.log(buf2.toString('utf8', 0, 3));

    // Prints: té
    console.log(buf2.toString(undefined, 0, 3));

### buf.values()#

Added in: 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.

Examples:

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

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

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

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

Added in: v0.1.90

- `string` <string> String to be written 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 a partial amount of `string` will be written. However, partially encoded characters will not be written.

Example:

    const buf = Buffer.allocUnsafe(256);

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

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

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

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

Added in: v0.11.15

- `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`.
- `noAssert` <boolean> Skip `value` and `offset` validation? Default: `false`
- 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.

Setting `noAssert` to `true` allows the encoded form of `value` to extend beyond the end of `buf`, but the result should be considered undefined behavior.

Examples:

    const buf = Buffer.allocUnsafe(8);

    buf.writeDoubleBE(0xdeadbeefcafebabe, 0);

    // Prints: <Buffer 43 eb d5 b7 dd f9 5f d7>
    console.log(buf);

    buf.writeDoubleLE(0xdeadbeefcafebabe, 0);

    // Prints: <Buffer d7 5f f9 dd b7 d5 eb 43>
    console.log(buf);

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

### buf.writeFloatLE(value, offset[, noAssert])#

Added in: v0.11.15

- `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`.
- `noAssert` <boolean> Skip `value` and `offset` validation? Default: `false`
- 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.

Setting `noAssert` to `true` allows the encoded form of `value` to extend beyond the end of `buf`, but the result should be considered undefined behavior.

Examples:

    const buf = Buffer.allocUnsafe(4);

    buf.writeFloatBE(0xcafebabe, 0);

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

    buf.writeFloatLE(0xcafebabe, 0);

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

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

Added in: v0.5.0

- `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`.
- `noAssert` <boolean> Skip `value` and `offset` validation? Default: `false`
- 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.

Setting `noAssert` to `true` allows the encoded form of `value` to extend beyond the end of `buf`, but the result should be considered undefined behavior.

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

Examples:

    const buf = Buffer.allocUnsafe(2);

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

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

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

### buf.writeInt16LE(value, offset[, noAssert])#

Added in: v0.5.5

- `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`.
- `noAssert` <boolean> Skip `value` and `offset` validation? Default: `false`
- 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.

Setting `noAssert` to `true` allows the encoded form of `value` to extend beyond the end of `buf`, but the result should be considered undefined behavior.

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

Examples:

    const buf = Buffer.allocUnsafe(4);

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

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

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

### buf.writeInt32LE(value, offset[, noAssert])#

Added in: v0.5.5

- `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`.
- `noAssert` <boolean> Skip `value` and `offset` validation? Default: `false`
- 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.

Setting `noAssert` to `true` allows the encoded form of `value` to extend beyond the end of `buf`, but the result should be considered undefined behavior.

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

Examples:

    const buf = Buffer.allocUnsafe(8);

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

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

### buf.writeIntBE(value, offset, byteLength[, noAssert])#

### buf.writeIntLE(value, offset, byteLength[, noAssert])#

Added in: v0.11.15

- `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`.
- `noAssert` <boolean> Skip `value`, `offset`, and `byteLength` validation? Default: `false`
- 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.

Setting `noAssert` to `true` allows the encoded form of `value` to extend beyond the end of `buf`, but the result should be considered undefined behavior.

Examples:

    const buf = Buffer.allocUnsafe(6);

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

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

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

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

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

Added in: v0.5.0

- `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`.
- `noAssert` <boolean> Skip `value` and `offset` validation? Default: `false`
- 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.

Setting `noAssert` to `true` allows the encoded form of `value` to extend beyond the end of `buf`, but the result should be considered undefined behavior.

Examples:

    const buf = Buffer.allocUnsafe(4);

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

    // Prints: <Buffer 03 04 23 42>
    console.log(buf);

### buf.writeUInt16BE(value, offset[, noAssert])#

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

Added in: v0.5.5

- `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`.
- `noAssert` <boolean> Skip `value` and `offset` validation? Default: `false`
- 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.

Setting `noAssert` to `true` allows the encoded form of `value` to extend beyond the end of `buf`, but the result should be considered undefined behavior.

Examples:

    const buf = Buffer.allocUnsafe(4);

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

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

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

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

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

### buf.writeUInt32LE(value, offset[, noAssert])#

Added in: v0.5.5

- `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`.
- `noAssert` <boolean> Skip `value` and `offset` validation? Default: `false`
- 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.

Setting `noAssert` to `true` allows the encoded form of `value` to extend beyond the end of `buf`, but the result should be considered undefined behavior.

Examples:

    const buf = Buffer.allocUnsafe(4);

    buf.writeUInt32BE(0xfeedface, 0);

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

    buf.writeUInt32LE(0xfeedface, 0);

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

### buf.writeUIntBE(value, offset, byteLength[, noAssert])#

### buf.writeUIntLE(value, offset, byteLength[, noAssert])#

Added in: v0.5.5

- `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`.
- `noAssert` <boolean> Skip `value`, `offset`, and `byteLength` validation? Default: `false`
- 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.

Setting `noAssert` to `true` allows the encoded form of `value` to extend beyond the end of `buf`, but the result should be considered undefined behavior.

Examples:

    const buf = Buffer.allocUnsafe(6);

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

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

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

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

## buffer.INSPECT_MAX_BYTES#

Added in: 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#

Added in: 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)#

History

Version | Changes
--- | ---
v8.0.0 | The `source` parameter can now be a `Uint8Array`.
v7.1.0 | Added in: v7.1.0

- `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.

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

    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#

Deprecated since: 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. This approach improves both performance and memory usage since v8 does not need to track and cleanup as many `Persistent` objects.

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.

Example:

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

    socket.on('readable', () => {
      const data = socket.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)#

Deprecated since: 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 the `size` is larger than `buffer.constants.MAX_LENGTH` or smaller than 0, a `RangeError` will be thrown. A zero-length `Buffer` will be 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)` to initialize a `SlowBuffer` to zeroes.

Example:

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

    const buf = new SlowBuffer(5);

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

    buf.fill(0);

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

## Buffer Constants#

Added in: 8.2.0

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#

Added in: 8.2.0

- <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#

Added in: 8.2.0

- <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.