# arraybuffer2buffer
> Allocate a [buffer][@stdlib/buffer/ctor] from an [ArrayBuffer][@stdlib/array/buffer].
## Usage
```javascript
var arraybuffer2buffer = require( '@stdlib/buffer/from-arraybuffer' );
```
#### arraybuffer2buffer( buf\[, byteOffset\[, length]] )
Allocates a [buffer][@stdlib/buffer/ctor] from an [`ArrayBuffer`][@stdlib/array/buffer].
```javascript
var ArrayBuffer = require( '@stdlib/array/buffer' );
var ab = new ArrayBuffer( 10 );
var buf = arraybuffer2buffer( ab );
// returns
```
By default, the function allocates a [buffer][@stdlib/buffer/ctor] starting from the first byte of the provided [`ArrayBuffer`][@stdlib/array/buffer]. To specify an alternative starting index, provide a `byteOffset`.
```javascript
var ArrayBuffer = require( '@stdlib/array/buffer' );
var ab = new ArrayBuffer( 10 );
var buf = arraybuffer2buffer( ab, 2 );
// returns
var len = buf.length;
// returns 8
```
By default, the function allocates a [buffer][@stdlib/buffer/ctor] until the end of the provided [`ArrayBuffer`][@stdlib/array/buffer]. To allocate a specified number of [`ArrayBuffer`][@stdlib/array/buffer] bytes, provide a `length`.
```javascript
var ArrayBuffer = require( '@stdlib/array/buffer' );
var ab = new ArrayBuffer( 10 );
var buf = arraybuffer2buffer( ab, 2, 4 );
// returns
var len = buf.length;
// returns 4
```
## Notes
The behavior of this function varies across Node.js versions due to changes in the underlying Node.js APIs:
- `<3.0.0`: the function copies [`ArrayBuffer`][@stdlib/array/buffer] bytes to a new [`Buffer`][@stdlib/buffer/ctor] instance.
- `>=3.0.0` and `<5.10.0`: if provided a `byteOffset`, the function copies [`ArrayBuffer`][@stdlib/array/buffer] bytes to a new [`Buffer`][@stdlib/buffer/ctor] instance; otherwise, the function returns a view of an [`ArrayBuffer`][@stdlib/array/buffer] without copying the underlying memory.
- `<6.0.0`: if provided an empty [`ArrayBuffer`][@stdlib/array/buffer], the function returns an empty [`Buffer`][@stdlib/buffer/ctor] which is **not** an [`ArrayBuffer`][@stdlib/array/buffer] view.
- `>=6.0.0`: the function returns a view of an [`ArrayBuffer`][@stdlib/array/buffer] without copying the underlying memory.
## Examples
```javascript
var ArrayBuffer = require( '@stdlib/array/buffer' );
var Float64Array = require( '@stdlib/array/float64' );
var randu = require( '@stdlib/random/base/randu' );
var IS_LITTLE_ENDIAN = require( '@stdlib/assert/is-little-endian' );
var arraybuffer2buffer = require( '@stdlib/buffer/from-arraybuffer' );
var high;
var view;
var low;
var buf;
var ab;
var i;
// Allocate an ArrayBuffer:
ab = new ArrayBuffer( 64 );
// Create a Float64 view and set random values:
view = new Float64Array( ab );
for ( i = 0; i < view.length; i++ ) {
view[ i ] = randu();
}
// Create a new buffer from the ArrayBuffer:
buf = arraybuffer2buffer( ab );
// Read the high and low words for each double:
for ( i = 0; i < view.length; i++ ) {
if ( IS_LITTLE_ENDIAN ) {
high = buf.readUInt32LE( (8*i)+4 );
low = buf.readUInt32LE( 8*i );
} else {
high = buf.readUInt32BE( 8*i );
low = buf.readUInt32BE( (8*i)+4 );
}
console.log( 'Value: %d. High: %d. Low: %d.', view[ i ], high, low );
}
```
[@stdlib/buffer/ctor]: https://www.npmjs.com/package/@stdlib/buffer/tree/main/ctor
[@stdlib/array/buffer]: https://www.npmjs.com/package/@stdlib/array-buffer