ArrayBuffer

Description

Resizing ArrayBuffers

ArrayBuffer objects can be made resizable by including the maxByteLength option when calling the ArrayBuffer() constructor. You can query whether an ArrayBuffer is resizable and what its maximum size is by accessing its resizable and maxByteLength properties, respectively. You can assign a new size to a resizable ArrayBuffer with a resize() call. New bytes are initialized to 0.

These features make resizing ArrayBuffers more efficient — otherwise, you have to make a copy of the buffer with a new size. It also gives JavaScript parity with WebAssembly in this regard (Wasm linear memory can be resized with WebAssembly.Memory.prototype.grow()).

Transferring ArrayBuffers

ArrayBuffer objects can be transferred between different execution contexts, like Web Workers or Service Workers, using the structured clone algorithm. This is done by passing the ArrayBuffer as a transferable object in a call to Worker.postMessage() or ServiceWorker.postMessage(). In pure JavaScript, you can also transfer the ownership of memory from one ArrayBuffer to another using its transfer() or transferToFixedLength() method.

When an ArrayBuffer is transferred, its original copy becomes detached — this means it is no longer usable. At any moment, there will only be one copy of the ArrayBuffer that actually has access to the underlying memory. Detached buffers have the following behaviors:

• byteLength becomes 0 (in both the buffer and the associated typed array views).
• Methods, such as resize() and slice(), throw a TypeError when invoked. The associated typed array views' methods also throw a TypeError.

You can check whether an ArrayBuffer is detached by its detached property.

Constructor

ArrayBuffer()

Creates a new ArrayBuffer object.

Static properties

ArrayBuffer[Symbol.species]

The constructor function that is used to create derived objects.

Static methods

ArrayBuffer.isView()

Returns true if arg is one of the ArrayBuffer views, such as typed array objects or a DataView. Returns false otherwise.

Instance properties

These properties are defined on ArrayBuffer.prototype and shared by all ArrayBuffer instances.

ArrayBuffer.prototype.byteLength

The size, in bytes, of the ArrayBuffer. This is established when the array is constructed and can only be changed using the ArrayBuffer.prototype.resize() method if the ArrayBuffer is resizable.

ArrayBuffer.prototype.constructor

The constructor function that created the instance object. For ArrayBuffer instances, the initial value is the ArrayBuffer constructor.

ArrayBuffer.prototype.detached

Read-only. Returns true if the ArrayBuffer has been detached (transferred), or false if not.

ArrayBuffer.prototype.maxByteLength

The read-only maximum length, in bytes, that the ArrayBuffer can be resized to. This is established when the array is constructed and cannot be changed.

ArrayBuffer.prototype.resizable

Read-only. Returns true if the ArrayBuffer can be resized, or false if not.

ArrayBuffer.prototype[Symbol.toStringTag]

The initial value of the [Symbol.toStringTag] property is the string "ArrayBuffer". This property is used in Object.prototype.toString().

Instance methods

ArrayBuffer.prototype.resize()

Resizes the ArrayBuffer to the specified size, in bytes.

ArrayBuffer.prototype.slice()

Returns a new ArrayBuffer whose contents are a copy of this ArrayBuffer's bytes from begin (inclusive) up to end (exclusive). If either begin or end is negative, it refers to an index from the end of the array, as opposed to from the beginning.

ArrayBuffer.prototype.transfer()

Creates a new ArrayBuffer with the same byte content as this buffer, then detaches this buffer.

ArrayBuffer.prototype.transferToFixedLength()

Creates a new non-resizable ArrayBuffer with the same byte content as this buffer, then detaches this buffer.

Examples

Creating an ArrayBuffer

In this example, we create a 8-byte buffer with an Int32Array view referring to the buffer:

const buffer = new ArrayBuffer(8);
const view = new Int32Array(buffer);

Specifications

Browser compatibility

See also

• Polyfill of ArrayBuffer in core-js
• JavaScript typed arrays guide
• SharedArrayBuffer
• RangeError: invalid array length