Atomics.notify() - JavaScript | MDN

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Atomics.notify()

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.

The Atomics.notify() static method notifies up some agents that are sleeping in the wait queue.

Note: This operation only works with an Int32Array or BigInt64Array that views a SharedArrayBuffer. It will return 0 on non-shared ArrayBuffer objects.

Syntax

Atomics.notify(typedArray, index, count)

Parameters

typedArray

An Int32Array or BigInt64Array that views a SharedArrayBuffer.

index

The position in the typedArray to wake up on.

count Optional

The number of sleeping agents to notify. Defaults to Infinity.

Return value

Returns the number of woken up agents, or 0 if typedArray is a view on a non-shared ArrayBuffer.

Exceptions

TypeError

Thrown if typedArray is not an Int32Array or BigInt64Array.

RangeError

Thrown if index is out of bounds in the typedArray.

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.

Using Atomics.notify()

Given a shared Int32Array:

js
const sab = new SharedArrayBuffer(1024);
const int32 = new Int32Array(sab);

A reading thread is sleeping and waiting on location 0 because the provided value matches what is stored at the provided index. The reading thread will not move on until the writing thread has called Atomics.notify() on position 0 of the provided typedArray. Note that if, after being woken up, the value of location 0 has not been changed by the writing thread, the reading thread will not go back to sleep, but will continue on.

js
Atomics.wait(int32, 0, 0);
console.log(int32[0]); // 123

A writing thread stores a new value and notifies the waiting thread once it has written:

js
console.log(int32[0]); // 0;
Atomics.store(int32, 0, 123);
Atomics.notify(int32, 0, 1);

Specifications

Specification

ECMAScript® 2027 Language Specification
# sec-atomics.notify

Browser compatibility

Enable JavaScript to view this browser compatibility table.

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This page was last modified on Feb 10, 2026 by MDN contributors.

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