# Buffer
<!--introduced_in=v0.10.0-->
> 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:
```js
// Creates a zero-filled Buffer of length 10.
const buf1 = Buffer.alloc(10);
// Creates a Buffer of length 10, filled with 0x1.
const buf2 = Buffer.alloc(10, 1);
// Creates an uninitialized buffer of length 10.
// This is faster than calling Buffer.alloc() but the returned
// Buffer instance might contain old data that needs to be
// overwritten using either fill() or write().
const buf3 = Buffer.allocUnsafe(10);
// Creates a Buffer containing [0x1, 0x2, 0x3].
const buf4 = Buffer.from([1, 2, 3]);
// Creates a Buffer containing UTF-8 bytes [0x74, 0xc3, 0xa9, 0x73, 0x74].
const buf5 = Buffer.from('tést');
// Creates a Buffer containing Latin-1 bytes [0x74, 0xe9, 0x73, 0x74].
const buf6 = Buffer.from('tést', 'latin1');
```
## `Buffer.from()`, `Buffer.alloc()`, and `Buffer.allocUnsafe()`
In versions of Node.js prior to 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. The memory allocated
for such `Buffer` instances is *not* initialized and *can contain sensitive
data*. Such `Buffer` instances *must* be initialized *manually* by using either
[`buf.fill(0)`][`buf.fill()`] 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`.
* 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()` 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]])`][`Buffer.from(arrayBuffer)`]
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])`][`Buffer.from(string)`] returns a new `Buffer`
containing a *copy* of the provided string.
* [`Buffer.alloc(size[, fill[, encoding]])`][`Buffer.alloc()`] returns a "filled"
`Buffer` instance of the specified size. This method can be significantly
slower than [`Buffer.allocUnsafe(size)`][`Buffer.allocUnsafe()`] but ensures
that newly created `Buffer` instances never contain old and potentially
sensitive data.
* [`Buffer.allocUnsafe(size)`][`Buffer.allocUnsafe()`] and
[`Buffer.allocUnsafeSlow(size)`][`Buffer.allocUnsafeSlow()`] each return a
new `Buffer` of the specified `size` whose content *must* be initialized
using either [`buf.fill(0)`][`buf.fill()`] 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
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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:
```txt
$ node --zero-fill-buffers
> Buffer.allocUnsafe(5);
<Buffer 00 00 00 00 00>
```
### What makes `Buffer.allocUnsafe()` and `Buffer.allocUnsafeSlow()` "unsafe"?
When calling [`Buffer.allocUnsafe()`] and [`Buffer.allocUnsafeSlow()`], the
segment of allocated memory is *uninitialized* (it is not zeroed-out). While
this design makes the allocation of memory quite fast, the allocated segment of
memory might contain old data that is potentially sensitive. Using a `Buffer`
created by [`Buffer.allocUnsafe()`] without *completely* overwriting the memory
can allow this old data to be leaked when the `Buffer` memory is read.
While there are clear performance advantages to using [`Buffer.allocUnsafe()`],
extra care *must* be taken in order to avoid introducing security
vulnerabilities into an application.
## Buffers and Character Encodings
`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:
```js
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 spec] 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 spec it's possible
that the server actually returned win-1252-encoded data, and using `'latin1'`
encoding may incorrectly decode the characters.
## Buffers and TypedArray
`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()`][`buf.slice()`] creates a view over the
existing `Buffer` without copying, making [`Buffer#slice()`][`buf.slice()`] far
more efficient.
It is also possible to create new [`TypedArray`] instances from a `Buffer` with
the following caveats:
1. The `Buffer` object's memory is copied to the [`TypedArray`], not shared.
2. The `Buffer` object's memory is interpreted as an array of distinct
elements, and not as a byte array of the target type. That is,
`new Uint32Array(Buffer.from([1, 2, 3, 4]))` creates a 4-element [`Uint32Array`]
with elements `[1, 2, 3, 4]`, not a [`Uint32Array`] with a single element
`[0x1020304]` or `[0x4030201]`.
It is possible to create a new `Buffer` that shares the same allocated memory as
a [`TypedArray`] instance by using the TypeArray object's `.buffer` property.
Example:
```js
const arr = new Uint16Array(2);
arr[0] = 5000;
arr[1] = 4000;
// Copies the contents of `arr`
const buf1 = Buffer.from(arr);
// Shares memory with `arr`
const buf2 = Buffer.from(arr.buffer);
// 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:
```js
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(arrayBuffer)`]
* [`Buffer.from(string[, encoding])`][`Buffer.from(string)`]
## Buffers and ES6 iteration
`Buffer` instances can be iterated over using the [`ECMAScript 2015`] (ES6) `for..of`
syntax.
Example:
```js
const buf = Buffer.from([1, 2, 3]);
// Prints:
// 1
// 2
// 3
for (const b of buf) {
console.log(b);
}
```
Additionally, the [`buf.values()`], [`buf.keys()`], and
[`buf.entries()`] methods can be used to create iterators.
## Class: Buffer
The `Buffer` class is a global type for dealing with binary data directly.
It can be constructed in a variety of ways.
### new Buffer(array)
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> 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:
```js
// Creates a new Buffer containing the UTF-8 bytes of the string 'buffer'
const buf = new Buffer([0x62, 0x75, 0x66, 0x66, 0x65, 0x72]);
```
### new Buffer(buffer)
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> 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:
```js
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(arrayBuffer[, byteOffset [, length]])
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> Stability: 0 - Deprecated: Use
> [`Buffer.from(arrayBuffer[, byteOffset [, length]])`][`Buffer.from(arrayBuffer)`]
> instead.
* `arrayBuffer` {ArrayBuffer|SharedArrayBuffer} An [`ArrayBuffer`],
[`SharedArrayBuffer`] or the `.buffer` property of a [`TypedArray`].
* `byteOffset` {integer} Index of first byte to expose. **Default:** `0`
* `length` {integer} Number of bytes to expose.
**Default:** `arrayBuffer.length - byteOffset`
This creates a view of the [`ArrayBuffer`] or [`SharedArrayBuffer`] without
copying the underlying memory. For example, when passed a reference to the
`.buffer` property of a [`TypedArray`] instance, the newly created `Buffer` will
share the same allocated memory as the [`TypedArray`].
The optional `byteOffset` and `length` arguments specify a memory range within
the `arrayBuffer` that will be shared by the `Buffer`.
Example:
```js
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(size)
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> 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. The `size` must be less than or equal
to the value of [`buffer.kMaxLength`]. Otherwise, a [`RangeError`] is thrown.
A zero-length `Buffer` will be created if `size <= 0`.
Unlike [`ArrayBuffers`][`ArrayBuffer`], the underlying memory for `Buffer` instances
created in this way is *not initialized*. The contents of a newly created `Buffer`
are unknown and *could contain sensitive data*. Use
[`Buffer.alloc(size)`][`Buffer.alloc()`] instead to initialize a `Buffer` to zeroes.
Example:
```js
const buf = new Buffer(10);
// Prints: (contents may vary): <Buffer 48 21 4b 00 00 00 00 00 30 dd>
console.log(buf);
buf.fill(0);
// Prints: <Buffer 00 00 00 00 00 00 00 00 00 00>
console.log(buf);
```
### new Buffer(string[, encoding])
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> Stability: 0 - Deprecated:
> Use [`Buffer.from(string[, encoding])`][`Buffer.from(string)`] instead.
* `string` {string} String to encode.
* `encoding` {string} The encoding of `string`. **Default:** `'utf8'`
Creates a new `Buffer` containing the given JavaScript string `string`. If
provided, the `encoding` parameter identifies the character encoding of `string`.
Examples:
```js
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]])
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* `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:
```js
const buf = Buffer.alloc(5);
// Prints: <Buffer 00 00 00 00 00>
console.log(buf);
```
The `size` must be less than or equal to the value of [`buffer.kMaxLength`].
Otherwise, a [`RangeError`] is thrown. A zero-length `Buffer` will be created if
`size <= 0`.
If `fill` is specified, the allocated `Buffer` will be initialized by calling
[`buf.fill(fill)`][`buf.fill()`].
Example:
```js
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)`][`buf.fill()`].
Example:
```js
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)
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* `size` {integer} The desired length of the new `Buffer`.
Allocates a new *non-zero-filled* `Buffer` of `size` bytes. The `size` must
be less than or equal to the value of [`buffer.kMaxLength`]. Otherwise, a
[`RangeError`] is thrown. A zero-length `Buffer` will be created if `size <= 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:
```js
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)
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* `size` {integer} The desired length of the new `Buffer`.
Allocates a new *non-zero-filled* and non-pooled `Buffer` of `size` bytes. The
`size` must be less than or equal to the value of [`buffer.kMaxLength`].
Otherwise, a [`RangeError`] is thrown. A zero-length `Buffer` will be created if
`size <= 0`.
The underlying memory for `Buffer` instances created in this way is *not
initialized*. The contents of the newly created `Buffer` are unknown and
*may contain sensitive data*. Use [`buf.fill(0)`][`buf.fill()`] to initialize such
`Buffer` instances 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:
```js
// 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])
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* `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.
*Note* that 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:
```js
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`]/
[`SharedArrayBuffer`], the actual byte length is returned.
Otherwise, converts to `String` and returns the byte length of string.
### Class Method: Buffer.compare(buf1, buf2)
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* `buf1` {Buffer}
* `buf2` {Buffer}
* Returns: {integer}
Compares `buf1` to `buf2` typically for the purpose of sorting arrays of
`Buffer` instances. This is equivalent to calling
[`buf1.compare(buf2)`][`buf.compare()`].
Example:
```js
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])
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* `list` {Array} List of `Buffer` 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
```js
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)
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* `array` {Array}
Allocates a new `Buffer` using an `array` of octets.
Example:
```js
// Creates a new Buffer containing UTF-8 bytes of the string 'buffer'
const buf = Buffer.from([0x62, 0x75, 0x66, 0x66, 0x65, 0x72]);
```
A `TypeError` will be thrown if `array` is not an `Array`.
### Class Method: Buffer.from(arrayBuffer[, byteOffset[, length]])
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* `arrayBuffer` {ArrayBuffer|SharedArrayBuffer} An [`ArrayBuffer`],
[`SharedArrayBuffer`], or the `.buffer` property of a [`TypedArray`].
* `byteOffset` {integer} Index of first byte to expose. **Default:** `0`
* `length` {integer} Number of bytes to expose.
**Default:** `arrayBuffer.length - byteOffset`
This creates a view of the [`ArrayBuffer`] without copying the underlying
memory. For example, when passed a reference to the `.buffer` property of a
[`TypedArray`] instance, the newly created `Buffer` will share the same
allocated memory as the [`TypedArray`].
Example:
```js
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:
```js
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`] or a
[`SharedArrayBuffer`].
### Class Method: Buffer.from(buffer)
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* `buffer` {Buffer} An existing `Buffer` to copy data from.
Copies the passed `buffer` data onto a new `Buffer` instance.
Example:
```js
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])
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-->
* `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:
```js
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.isBuffer(obj)
<!-- YAML
added: v0.1.101
-->
* `obj` {Object}
* Returns: {boolean}
Returns `true` if `obj` is a `Buffer`, `false` otherwise.
### Class Method: Buffer.isEncoding(encoding)
<!-- YAML
added: v0.9.1
-->
* `encoding` {string} A character encoding name to check.
* Returns: {boolean}
Returns `true` if `encoding` contains a supported character encoding, or `false`
otherwise.
### Class Property: Buffer.poolSize
<!-- YAML
added: v0.11.3
-->
* {integer} **Default:** `8192`
This is the number of bytes used to determine the size of pre-allocated, internal
`Buffer` instances used for pooling. This value may be modified.
### buf[index]
<!-- YAML
type: property
name: [index]
-->
The index operator `[index]` can be used to get and set the octet at position
`index` in `buf`. The values refer to individual bytes, so the legal value
range is between `0x00` and `0xFF` (hex) or `0` and `255` (decimal).
This operator is inherited from `Uint8Array`, so its behavior on out-of-bounds
access is the same as `UInt8Array` - that is, getting returns `undefined` and
setting does nothing.
Example: Copy an ASCII string into a `Buffer`, one byte at a time
```js
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.compare(target[, targetStart[, targetEnd[, sourceStart[, sourceEnd]]]])
<!-- YAML
added: v0.11.13
-->
* `target` {Buffer} A `Buffer` 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). **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.
Examples:
```js
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:
```js
const buf1 = Buffer.from([1, 2, 3, 4, 5, 6, 7, 8, 9]);
const buf2 = Buffer.from([5, 6, 7, 8, 9, 1, 2, 3, 4]);
// 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]]])
<!-- YAML
added: v0.1.90
-->
* `target` {Buffer|Uint8Array} A `Buffer` or [`Uint8Array`] to copy into.
* `targetStart` {integer} The offset within `target` at which to begin
copying to. **Default:** `0`
* `sourceStart` {integer} The offset within `buf` at which to begin copying from.
**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`.
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`
```js
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`
```js
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()
<!-- YAML
added: 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`
```js
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)
<!-- YAML
added: v0.11.13
-->
* `otherBuffer` {Buffer} A `Buffer` to compare to.
* Returns: {boolean}
Returns `true` if both `buf` and `otherBuffer` have exactly the same bytes,
`false` otherwise.
Examples:
```js
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])
<!-- YAML
added: 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'`
```js
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
```js
// Prints: <Buffer c8 a2 c8>
console.log(Buffer.allocUnsafe(3).fill('\u0222'));
```
### buf.includes(value[, byteOffset][, encoding])
<!-- YAML
added: v5.3.0
-->
* `value` {string|Buffer|integer} What to search for.
* `byteOffset` {integer} Where to begin searching in `buf`. **Default:** `0`
* `encoding` {string} If `value` is a string, this is its encoding.
**Default:** `'utf8'`
* Returns: {boolean} `true` if `value` was found in `buf`, `false` otherwise.
Equivalent to [`buf.indexOf() !== -1`][`buf.indexOf()`].
Examples:
```js
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])
<!-- YAML
added: v1.5.0
-->
* `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: {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`, `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:
```js
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()`].
```js
const b = Buffer.from('abcdef');
// Passing a value that's a number, but not a valid byte
// Prints: 2, equivalent to searching for 99 or 'c'
console.log(b.indexOf(99.9));
console.log(b.indexOf(256 + 99));
// Passing a byteOffset that coerces to NaN or 0
// Prints: 1, searching the whole buffer
console.log(b.indexOf('b', undefined));
console.log(b.indexOf('b', {}));
console.log(b.indexOf('b', null));
console.log(b.indexOf('b', []));
```
### buf.includes(value[, byteOffset][, encoding])
<!-- YAML
added: v5.3.0
-->
* `value` {String|Buffer|Integer} What to search for.
* `byteOffset` {Integer} Where to begin searching in `buf`. **Default:** `0`
* `encoding` {String} If `value` is a string, this is its encoding.
**Default:** `'utf8'`
* Returns: {Boolean} `true` if `value` was found in `buf`, `false` otherwise
Equivalent to [`buf.indexOf() !== -1`][`buf.indexOf()`].
Examples:
```js
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.keys()
<!-- YAML
added: v1.1.0
-->
* Returns: {Iterator}
Creates and returns an [iterator] of `buf` keys (indices).
Example:
```js
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])
<!-- YAML
added: v6.0.0
-->
* `value` {string|Buffer|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:
```js
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()`].
```js
const b = Buffer.from('abcdef');
// Passing a value that's a number, but not a valid byte
// Prints: 2, equivalent to searching for 99 or 'c'
console.log(b.lastIndexOf(99.9));
console.log(b.lastIndexOf(256 + 99));
// Passing a byteOffset that coerces to NaN
// Prints: 1, searching the whole buffer
console.log(b.lastIndexOf('b', undefined));
console.log(b.lastIndexOf('b', {}));
// Passing a byteOffset that coerces to 0
// Prints: -1, equivalent to passing 0
console.log(b.lastIndexOf('b', null));
console.log(b.lastIndexOf('b', []));
```
### buf.length
<!-- YAML
added: v0.1.90
-->
* {integer}
Returns the amount of memory allocated for `buf` in bytes. Note that this
does not necessarily reflect the amount of "usable" data within `buf`.
Example: Create a `Buffer` and write a shorter ASCII string to it
```js
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:
```js
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.readDoubleBE(offset[, noAssert])
### buf.readDoubleLE(offset[, noAssert])
<!-- YAML
added: 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 resulting behavior is undefined.
Examples:
```js
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])
<!-- YAML
added: 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 resulting behavior is undefined.
Examples:
```js
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])
<!-- YAML
added: 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 resulting behavior is undefined.
Integers read from a `Buffer` are interpreted as two's complement signed values.
Examples:
```js
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])
<!-- YAML
added: 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 resulting behavior is undefined.
Integers read from a `Buffer` are interpreted as two's complement signed values.
Examples:
```js
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])
<!-- YAML
added: 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 resulting behavior is undefined.
Integers read from a `Buffer` are interpreted as two's complement signed values.
Examples:
```js
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])
<!-- YAML
added: 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 resulting behavior is undefined.
Examples:
```js
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])
<!-- YAML
added: 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 resulting behavior is undefined.
Examples:
```js
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])
<!-- YAML
added: 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 resulting behavior is undefined.
Examples:
```js
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])
<!-- YAML
added: 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 resulting behavior is undefined.
Examples:
```js
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])
<!-- YAML
added: 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 resulting behavior is undefined.
Examples:
```js
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]])
<!-- YAML
added: 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.
**Note that 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`
```js
const buf1 = Buffer.allocUnsafe(26);
for (let i = 0; i < 26; i++) {
// 97 is the decimal ASCII value for 'a'
buf1[i] = i + 97;
}
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:
```js
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()
<!-- YAML
added: v5.10.0
-->
* Returns: {Buffer} A reference to `buf`.
Interprets `buf` as an array of unsigned 16-bit integers and swaps the byte-order
*in-place*. Throws a `RangeError` if [`buf.length`] is not a multiple of 2.
Examples:
```js
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()
<!-- YAML
added: v5.10.0
-->
* Returns: {Buffer} A reference to `buf`.
Interprets `buf` as an array of unsigned 32-bit integers and swaps the byte-order
*in-place*. Throws a `RangeError` if [`buf.length`] is not a multiple of 4.
Examples:
```js
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()
<!-- YAML
added: 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:
```js
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.toString([encoding[, start[, end]]])
<!-- YAML
added: 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`.
Examples:
```js
const buf1 = Buffer.allocUnsafe(26);
for (let i = 0; i < 26; i++) {
// 97 is the decimal ASCII value for 'a'
buf1[i] = i + 97;
}
// 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.toJSON()
<!-- YAML
added: v0.9.2
-->
* Returns: {Object}
Returns a JSON representation of `buf`. [`JSON.stringify()`] implicitly calls
this function when stringifying a `Buffer` instance.
Example:
```js
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.values()
<!-- YAML
added: v1.1.0
-->
* Returns: {Iterator}
Creates and returns an [iterator] for `buf` values (bytes). This function is
called automatically when a `Buffer` is used in a `for..of` statement.
Examples:
```js
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])
<!-- YAML
added: 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:
```js
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])
<!-- YAML
added: 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 resulting behavior is undefined.
Examples:
```js
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])
<!-- YAML
added: 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 resulting behavior is undefined.
Examples:
```js
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])
<!-- YAML
added: 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 resulting behavior is undefined.
`value` is interpreted and written as a two's complement signed integer.
Examples:
```js
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])
<!-- YAML
added: 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 resulting behavior is undefined.
`value` is interpreted and written as a two's complement signed integer.
Examples:
```js
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])
<!-- YAML
added: 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 resulting behavior is undefined.
`value` is interpreted and written as a two's complement signed integer.
Examples:
```js
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])
<!-- YAML
added: 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 resulting behavior is undefined.
Examples:
```js
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);
```
### buf.writeUInt8(value, offset[, noAssert])
<!-- YAML
added: 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 resulting behavior is undefined.
Examples:
```js
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])
<!-- YAML
added: 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 resulting behavior is undefined.
Examples:
```js
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])
<!-- YAML
added: 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 resulting behavior is undefined.
Examples:
```js
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])
<!-- YAML
added: 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 resulting behavior is undefined.
Examples:
```js
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);
```
## buffer.INSPECT_MAX_BYTES
<!-- YAML
added: v0.5.4
-->
* {integer} **Default:** `50`
Returns the maximum number of bytes that will be returned when
`buf.inspect()` is called. This can be overridden by user modules. See
[`util.inspect()`] for more details on `buf.inspect()` behavior.
Note that this is a property on the `buffer` module as returned by
`require('buffer')`, not on the `Buffer` global or a `Buffer` instance.
## buffer.kMaxLength
<!-- YAML
added: v3.0.0
-->
* {integer} The largest size allowed for a single `Buffer` instance.
On 32-bit architectures, this value is `(2^30)-1` (~1GB).
On 64-bit architectures, this value is `(2^31)-1` (~2GB).
## Class: SlowBuffer
<!-- YAML
deprecated: v6.0.0
-->
> Stability: 0 - Deprecated: Use [`Buffer.allocUnsafeSlow()`] instead.
Returns an un-pooled `Buffer`.
In order to avoid the garbage collection overhead of creating many individually
allocated `Buffer` instances, by default allocations under 4KB are sliced from a
single larger allocated object. 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:
```js
// 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)
<!-- YAML
deprecated: v6.0.0
-->
> Stability: 0 - Deprecated: Use [`Buffer.allocUnsafeSlow()`] instead.
* `size` {integer} The desired length of the new `SlowBuffer`.
Allocates a new `SlowBuffer` of `size` bytes. The `size` must be less than
or equal to the value of [`buffer.kMaxLength`]. Otherwise, a [`RangeError`] is
thrown. A zero-length `Buffer` will be created if `size <= 0`.
The underlying memory for `SlowBuffer` instances is *not initialized*. The
contents of a newly created `SlowBuffer` are unknown and could contain
sensitive data. Use [`buf.fill(0)`][`buf.fill()`] to initialize a `SlowBuffer` to zeroes.
Example:
```js
const SlowBuffer = require('buffer').SlowBuffer;
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);
```
[`buf.compare()`]: #buffer_buf_compare_target_targetstart_targetend_sourcestart_sourceend
[`buf.entries()`]: #buffer_buf_entries
[`buf.indexOf()`]: #buffer_buf_indexof_value_byteoffset_encoding
[`buf.fill()`]: #buffer_buf_fill_value_offset_end_encoding
[`buf.keys()`]: #buffer_buf_keys
[`buf.length`]: #buffer_buf_length
[`buf.slice()`]: #buffer_buf_slice_start_end
[`buf.values()`]: #buffer_buf_values
[`buffer.kMaxLength`]: #buffer_buffer_kmaxlength
[`Buffer.alloc()`]: #buffer_class_method_buffer_alloc_size_fill_encoding
[`Buffer.allocUnsafe()`]: #buffer_class_method_buffer_allocunsafe_size
[`Buffer.allocUnsafeSlow()`]: #buffer_class_method_buffer_allocunsafeslow_size
[`Buffer.from(array)`]: #buffer_class_method_buffer_from_array
[`Buffer.from(arrayBuffer)`]: #buffer_class_method_buffer_from_arraybuffer_byteoffset_length
[`Buffer.from(buffer)`]: #buffer_class_method_buffer_from_buffer
[`Buffer.from(string)`]: #buffer_class_method_buffer_from_string_encoding
[`Buffer.poolSize`]: #buffer_class_property_buffer_poolsize
[`RangeError`]: errors.html#errors_class_rangeerror
[`util.inspect()`]: util.html#util_util_inspect_object_options
[`ArrayBuffer`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer
[`ArrayBuffer#slice()`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer/slice
[`DataView`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView
[iterator]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols
[`JSON.stringify()`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON/stringify
[RFC1345]: https://tools.ietf.org/html/rfc1345
[RFC4648, Section 5]: https://tools.ietf.org/html/rfc4648#section-5
[`String.prototype.length`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/length
[`SharedArrayBuffer`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/SharedArrayBuffer
[`String#indexOf()`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/indexOf
[`String#lastIndexOf()`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/lastIndexOf
[`TypedArray`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray
[`TypedArray.from()`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray/from
[`Uint32Array`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint32Array
[`Uint8Array`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array
[WHATWG spec]: https://encoding.spec.whatwg.org/
[`ECMAScript 2015`]: https://www.ecma-international.org/ecma-262/6.0/index.html
