SharedArrayBuffer() constructor
Baseline
Widely available
*
This feature is well established and works across many devices and browser versions. It’s been available across browsers since December 2021.
* Some parts of this feature may have varying levels of support.
Note:
The SharedArrayBuffer constructor may not always be globally available unless certain security requirements are met.
The SharedArrayBuffer() constructor creates SharedArrayBuffer objects.
Syntax
new SharedArrayBuffer(length)
new SharedArrayBuffer(length, options)
Parameters
length-
The size, in bytes, of the array buffer to create.
optionsOptional-
An object, which can contain the following properties:
maxByteLengthOptional-
The maximum size, in bytes, that the shared array buffer can be resized to.
Return value
A new SharedArrayBuffer object of the specified size, with its maxByteLength property set to the specified maxByteLength if one was specified. Its contents are initialized to 0.
Examples
Note that these examples cannot be run directly from the console or an arbitrary web page, because SharedArrayBuffer is not defined unless its security requirements are met.
Basic usage
Create a buffer specifying its size in bytes.
// Create a SharedArrayBuffer with a size in bytes
const buffer = new SharedArrayBuffer(8);
console.log(buffer.byteLength); // 8
Always use the new operator to create a SharedArrayBuffer
SharedArrayBuffer constructors are required to be constructed with a new operator. Calling a SharedArrayBuffer constructor as a function without new will throw a TypeError.
const sab = SharedArrayBuffer(1024);
// TypeError: calling a builtin SharedArrayBuffer constructor
// without new is forbidden
const sab = new SharedArrayBuffer(1024);
Growing a growable SharedArrayBuffer
In this example, we create an 8-byte buffer that is growable to a max length of 16 bytes, then grow() it to 12 bytes:
const buffer = new SharedArrayBuffer(8, { maxByteLength: 16 });
buffer.grow(12);
Note:
It is recommended that maxByteLength is set to the smallest value possible for your use case. It should never exceed 1073741824 (1GB), to reduce the risk of out-of-memory errors.
Specifications
| Specification |
|---|
| ECMAScript® 2026 Language Specification # sec-sharedarraybuffer-constructor |