ArrayBuffer
The ArrayBuffer
object is used to represent a generic raw binary data buffer.
It is an array of bytes, often referred to in other languages as a "byte array". You cannot directly manipulate the contents of an ArrayBuffer
; instead, you create one of the typed array objects or a DataView
object which represents the buffer in a specific format, and use that to read and write the contents of the buffer.
The ArrayBuffer()
constructor creates a new ArrayBuffer
of the given length in bytes. You can also get an array buffer from existing data, for example, from a Base64 string or from a local file.
ArrayBuffer
is a transferable object.
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 ArrayBuffer
s 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()
andslice()
, throw aTypeError
when invoked. The associated typed array views' methods also throw aTypeError
.
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
ifarg
is one of the ArrayBuffer views, such as typed array objects or aDataView
. Returnsfalse
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 theArrayBuffer.prototype.resize()
method if theArrayBuffer
is resizable. ArrayBuffer.prototype.constructor
-
The constructor function that created the instance object. For
ArrayBuffer
instances, the initial value is theArrayBuffer
constructor. ArrayBuffer.prototype.detached
-
Read-only. Returns
true
if theArrayBuffer
has been detached (transferred), orfalse
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 theArrayBuffer
can be resized, orfalse
if not. ArrayBuffer.prototype[Symbol.toStringTag]
-
The initial value of the
[Symbol.toStringTag]
property is the string"ArrayBuffer"
. This property is used inObject.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 thisArrayBuffer
's bytes frombegin
(inclusive) up toend
(exclusive). If eitherbegin
orend
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 a Int32Array
view referring to the buffer:
const buffer = new ArrayBuffer(8);
const view = new Int32Array(buffer);
Specifications
Specification |
---|
ECMAScript Language Specification # sec-arraybuffer-objects |
Browser compatibility
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