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# Buffer#

Stability: 2 - Stable

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

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

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

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

    // 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)` or by writing to the entire `Buffer`. While this behavior is intentional to improve performance, development experience has demonstrated that a more explicit distinction is required between creating a fast-but-uninitialized `Buffer` versus creating a slower-but-safer `Buffer`. Since Node.js 8.0.0, `Buffer(num)` and `new Buffer(num)` return a `Buffer` with initialized memory.
- Passing a string, array, or `Buffer` as the first argument copies the passed object's data into the `Buffer`.
- Passing an `ArrayBuffer` or a `SharedArrayBuffer` returns a `Buffer` that shares allocated memory with the given array buffer.

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

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

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

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

- `Buffer.from(array)` returns a new `Buffer` that contains a copy of the provided octets.
- `Buffer.from(arrayBuffer[, byteOffset[, length]])` 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])` returns a new `Buffer` that contains a copy of the provided string.
- `Buffer.alloc(size[, fill[, encoding]])` returns a new initialized `Buffer` of the specified size. This method is slower than `Buffer.allocUnsafe(size)` but guarantees that newly created `Buffer` instances never contain old data that is potentially sensitive. A `TypeError` will be thrown if `size` is not a number.
- `Buffer.allocUnsafe(size)` and `Buffer.allocUnsafeSlow(size)` 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#

Added in: v5.10.0

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

    $ node --zero-fill-buffers
    > Buffer.allocUnsafe(5);
    <Buffer 00 00 00 00 00>

### What makes `Buffer.allocUnsafe()` and `Buffer.allocUnsafeSlow()` "unsafe"?#

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

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

## 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.

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

    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. Data truncation may occur for unsanitized input. For example:

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

    Buffer.from('1a7g', 'hex');
    // Prints <Buffer 1a>, data truncated when data ends in single digit ('7').

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

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

## Buffers and 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 `TypedArray`. 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 `TypedArray` object's `.buffer` property.

    const arr = new Uint16Array(2);

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

    // Copies the contents of `arr`.
    const buf1 = Buffer.from(arr);
    // Shares memory with `arr`.
    const buf2 = Buffer.from(arr.buffer);

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

    arr[1] = 6000;

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

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

    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(string[, encoding])`

## Buffers and iteration#

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

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

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

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

## Class: `Buffer`#

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

### `new Buffer(array)`#

History

Version | Changes
--- | ---
v10.0.0 | Calling this constructor emits a deprecation warning when run from code outside the `node_modules` directory.
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.

    // 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
--- | ---
v10.0.0 | Calling this constructor emits a deprecation warning when run from code outside the `node_modules` directory.
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> | <SharedArrayBuffer> An `ArrayBuffer`, `SharedArrayBuffer` or the `.buffer` property of a `TypedArray`.
- `byteOffset` <integer> Index of first byte to expose. Default: `0`.
- `length` <integer> Number of bytes to expose. Default: `arrayBuffer.byteLength - byteOffset`.

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`.

    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)`#

History

Version | Changes
--- | ---
v10.0.0 | Calling this constructor emits a deprecation warning when run from code outside the `node_modules` directory.
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> | <Uint8Array> An existing `Buffer` or `Uint8Array` from which to copy data.

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

    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)`#

History

Version | Changes
--- | ---
v10.0.0 | Calling this constructor emits a deprecation warning when run from code outside the `node_modules` directory.
v8.0.0 | The `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 `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)` instead to initialize a `Buffer` with zeroes.

    const buf = new Buffer(10);

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

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

History

Version | Changes
--- | ---
v10.0.0 | Calling this constructor emits a deprecation warning when run from code outside the `node_modules` directory.
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 `string`. The `encoding` parameter identifies the character encoding of `string`.

    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]])`#

History

Version | Changes
--- | ---
v10.0.0 | Attempting to fill a non-zero length buffer with a zero length buffer triggers a thrown exception.
v10.0.0 | Specifying an invalid string for `fill` triggers a thrown exception.
v8.9.3 | Specifying an invalid string for `fill` now results in a zero-filled buffer.
v5.10.0 | Added in: v5.10.0

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

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

    const buf = Buffer.alloc(5);

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

If `size` is larger than `buffer.constants.MAX_LENGTH` or smaller than 0, `ERR_INVALID_OPT_VALUE` is thrown. A zero-length `Buffer` is created if `size` is 0.

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

    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)`.

    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)`#

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 `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.

    const buf = Buffer.allocUnsafe(10);

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

    buf.fill(0);

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

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

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

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

### Class Method: `Buffer.allocUnsafeSlow(size)`#

Added in: 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)` 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.

    // 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])`#

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> | <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.

    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)`#

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)`.

    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])`#

History

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

- `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`.

    // 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)`#

Added in: v5.10.0

- `array` <integer[]>

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

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

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

### Class Method: `Buffer.from(arrayBuffer[, byteOffset[, length]])`#

Added in: 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.byteLength - byteOffset`.

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

    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`.

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

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

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

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

Added in: 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.

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

    buf1[0] = 0x61;

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

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

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

Added in: v8.2.0

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

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

    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)`.

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

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

A `TypeError` will be thrown if `object` has not mentioned methods or is not of other type appropriate for `Buffer.from()` variants.

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

Added in: 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`.

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

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

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

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

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.

    console.log(Buffer.isEncoding('utf-8'));
    // Prints: true

    console.log(Buffer.isEncoding('hex'));
    // Prints: true

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

    console.log(Buffer.isEncoding(''));
    // Prints: false

### Class Property: `Buffer.poolSize`#

Added in: 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]`#

- `index` <integer>

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

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

    // 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.

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

    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:

    // 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]]]])`#

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` with which to compare `buf`.
- `targetStart` <integer> The offset within `target` at which to begin comparison. Default: `0`.
- `targetEnd` <integer> The offset within `target` at which to end comparison (not inclusive). Default: `target.length`.
- `sourceStart` <integer> The offset within `buf` at which to begin comparison. Default: `0`.
- `sourceEnd` <integer> The offset within `buf` at which to end comparison (not inclusive). Default: `buf.length`.
- Returns: <integer>

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

- `0` is returned if `target` is the same as `buf`
- `1` is returned if `target` should come before `buf` when sorted.
- `-1` is returned if `target` should come after `buf` when sorted.

    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.

    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]]])`#

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 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`.

    // 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!!!!!!!!!!!!!

    // 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()`#

Added in: v1.1.0

- Returns: <Iterator>

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

    // 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)`#

History

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

- `otherBuffer` <Buffer> | <Uint8Array> A `Buffer` or `Uint8Array` with which to compare `buf`.
- Returns: <boolean>

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

    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])`#

History

Version | Changes
--- | ---
v11.0.0 | Throws `ERR_OUT_OF_RANGE` instead of `ERR_INDEX_OUT_OF_RANGE`.
v10.0.0 | Negative `end` values throw an `ERR_INDEX_OUT_OF_RANGE` error.
v10.0.0 | Attempting to fill a non-zero length buffer with a zero length buffer triggers a thrown exception.
v10.0.0 | Specifying an invalid string for `value` triggers a thrown exception.
v5.7.0 | The `encoding` parameter is supported now.
v0.5.0 | Added in: v0.5.0

- `value` <string> | <Buffer> | <Uint8Array> | <integer> The value with which to fill `buf`.
- `offset` <integer> Number of bytes to skip before starting to fill `buf`. Default: `0`.
- `end` <integer> Where to stop filling `buf` (not inclusive). Default: `buf.length`.
- `encoding` <string> The encoding for `value` if `value` is a string. Default: `'utf8'`.
- Returns: <Buffer> A reference to `buf`.

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

    // 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:

    // 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:

    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])`#

Added in: v5.3.0

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

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

    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])`#

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`. If negative, then offset is calculated from the end of `buf`. Default: `0`.
- `encoding` <string> If `value` is a string, this is the encoding used to determine the binary representation of the string that will be searched for in `buf`. Default: `'utf8'`.
- Returns: <integer> The index of the first occurrence of `value` in `buf`, or `-1` if `buf` does not contain `value`.

If `value` is:

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

    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()`.

    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).

    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])`#

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`. If negative, then offset is calculated from the end of `buf`. Default: `buf.length - 1`.
- `encoding` <string> If `value` is a string, this is the encoding used to determine the binary representation of the string that will be searched for in `buf`. Default: `'utf8'`.
- Returns: <integer> The index of the last occurrence of `value` in `buf`, or `-1` if `buf` does not contain `value`.

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

    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()`.

    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. This does not necessarily reflect the amount of "usable" data within `buf`.

    // 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`.

    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`#

Deprecated since: v8.0.0

Stability: 0 - Deprecated: Use `buf.buffer` instead.

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

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

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

Added in: v12.0.0

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

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

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

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

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

Added in: v12.0.0

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

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

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

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

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

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

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

History

Version | Changes
--- | ---
v10.0.0 | Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore.
v0.11.15 | Added in: v0.11.15

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

Reads a 64-bit double from `buf` at the specified `offset` with specified endian format (`readDoubleBE()` returns big endian, `readDoubleLE()` returns little endian).

    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])`#

History

Version | Changes
--- | ---
v10.0.0 | Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore.
v0.11.15 | Added in: v0.11.15

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

Reads a 32-bit float from `buf` at the specified `offset` with specified endian format (`readFloatBE()` returns big endian, `readFloatLE()` returns little endian).

    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])`#

History

Version | Changes
--- | ---
v10.0.0 | Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore.
v0.5.0 | Added in: v0.5.0

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

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

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

    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])`#

History

Version | Changes
--- | ---
v10.0.0 | Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore.
v0.5.5 | Added in: v0.5.5

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

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

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

    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])`#

History

Version | Changes
--- | ---
v10.0.0 | Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore.
v0.5.5 | Added in: v0.5.5

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

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

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

    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)`#

History

Version | Changes
--- | ---
v10.0.0 | Removed `noAssert` and no implicit coercion of the offset and `byteLength` to `uint32` anymore.
v0.11.15 | 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`.
- 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.

    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])`#

History

Version | Changes
--- | ---
v10.0.0 | Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore.
v0.5.0 | Added in: v0.5.0

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

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

    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])`#

History

Version | Changes
--- | ---
v10.0.0 | Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore.
v0.5.5 | Added in: v0.5.5

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

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

    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])`#

History

Version | Changes
--- | ---
v10.0.0 | Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore.
v0.5.5 | Added in: v0.5.5

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

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

    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)`#

History

Version | Changes
--- | ---
v10.0.0 | Removed `noAssert` and no implicit coercion of the offset and `byteLength` to `uint32` anymore.
v0.11.15 | 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`.
- 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.

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

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

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

Added in: v3.0.0

- `start` <integer> Where the new `Buffer` will start. Default: `0`.
- `end` <integer> Where the new `Buffer` will end (not inclusive). Default: `buf.length`.
- Returns: <Buffer>

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

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

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

    // Create a `Buffer` with the ASCII alphabet, take a slice, and modify one byte
    // from the original `Buffer`.

    const buf1 = Buffer.allocUnsafe(26);

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

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

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

    buf1[0] = 33;

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

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

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

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

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

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

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

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.

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

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

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

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

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

### `buf.swap16()`#

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 `ERR_INVALID_BUFFER_SIZE` if `buf.length` is not a multiple of 2.

    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:

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

### `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 `ERR_INVALID_BUFFER_SIZE` if `buf.length` is not a multiple of 4.

    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()`#

Added in: 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.

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

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

    buf1.swap64();

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

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

    buf2.swap64();
    // Throws ERR_INVALID_BUFFER_SIZE.

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

### `buf.toJSON()`#

Added in: v0.9.2

- Returns: <Object>

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

    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]]])`#

Added in: 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`. If a byte sequence in the input is not valid in the given `encoding` then it is replaced with the replacement character `U+FFFD`.

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

    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()`#

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.

    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])`#

Added in: 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.

    const buf = Buffer.alloc(256);

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

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

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

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

Added in: v12.0.0

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

Writes `value` to `buf` at the specified `offset` with specified endian format (`writeBigInt64BE()` writes big endian, `writeBigInt64LE()` writes little endian).

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

    const buf = Buffer.allocUnsafe(8);

    buf.writeBigInt64BE(0x0102030405060708n, 0);

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

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

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

Added in: v12.0.0

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

Writes `value` to `buf` at the specified `offset` with specified endian format (`writeBigUInt64BE()` writes big endian, `writeBigUInt64LE()` writes little endian).

    const buf = Buffer.allocUnsafe(8);

    buf.writeBigUInt64LE(0xdecafafecacefaden, 0);

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

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

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

History

Version | Changes
--- | ---
v10.0.0 | Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore.
v0.11.15 | 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`. Default: `0`.
- Returns: <integer> `offset` plus the number of bytes written.

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

    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])`#

History

Version | Changes
--- | ---
v10.0.0 | Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore.
v0.11.15 | 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`. Default: `0`.
- Returns: <integer> `offset` plus the number of bytes written.

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

    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])`#

History

Version | Changes
--- | ---
v10.0.0 | Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore.
v0.5.0 | 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`. Default: `0`.
- Returns: <integer> `offset` plus the number of bytes written.

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

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

    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])`#

History

Version | Changes
--- | ---
v10.0.0 | Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore.
v0.5.5 | 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`. Default: `0`.
- Returns: <integer> `offset` plus the number of bytes written.

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

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

    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])`#

History

Version | Changes
--- | ---
v10.0.0 | Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore.
v0.5.5 | 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`. Default: `0`.
- Returns: <integer> `offset` plus the number of bytes written.

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

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

    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)`#

History

Version | Changes
--- | ---
v10.0.0 | Removed `noAssert` and no implicit coercion of the offset and `byteLength` to `uint32` anymore.
v0.11.15 | 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`.
- 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.

    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])`#

History

Version | Changes
--- | ---
v10.0.0 | Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore.
v0.5.0 | 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`. Default: `0`.
- Returns: <integer> `offset` plus the number of bytes written.

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

    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])`#

History

Version | Changes
--- | ---
v10.0.0 | Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore.
v0.5.5 | 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`. Default: `0`.
- Returns: <integer> `offset` plus the number of bytes written.

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

    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])`#

History

Version | Changes
--- | ---
v10.0.0 | Removed `noAssert` and no implicit coercion of the offset to `uint32` anymore.
v0.5.5 | 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`. Default: `0`.
- Returns: <integer> `offset` plus the number of bytes written.

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

    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)`#

History

Version | Changes
--- | ---
v10.0.0 | Removed `noAssert` and no implicit coercion of the offset and `byteLength` to `uint32` anymore.
v0.5.5 | 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`.
- 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.

    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`#

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.

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`.

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.
- Returns: <Buffer>

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

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

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

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

    const buffer = require('buffer');

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

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

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

## Class: `SlowBuffer`#

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.

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.

    // 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)`#

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 `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)` to initialize a `SlowBuffer` with zeroes.

    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#

Added in: v8.2.0

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

### `buffer.constants.MAX_LENGTH`#

Added in: 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`#

Added in: 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.