This is an experimental technology
Because this technology's specification has not stabilized, check the compatibility table for usage in various browsers. Also note that the syntax and behavior of an experimental technology is subject to change in future versions of browsers as the specification changes.

The static Atomics.wait() method verifies that a given position in an Int32Array still contains a given value and sleeps awaiting or times out. It returns a string which is either "ok", "not-equal", or "timed-out".

Note: This operation only works with a shared Int32Array and is not allowed on the main thread.


Atomics.wait(typedArray, index, value[, timeout])


A shared Int32Array.
The position in the typedArray to wait on.
The expected value to test .
timeout Optional
Time to wait in milliseconds. Infinity, if no time is provided.

Return value

A String which is either "ok", "not-equal", or "timed-out".



Given a shared Int32Array:

var sab = new SharedArrayBuffer(1024);
var int32 = new Int32Array(sab);

A reading thread is sleeping and waiting on location 0 which is expected to be 0. As long as that is true, it will not go on. However, once the writing thread has stored a new value, it will be woken up by the writing thread and return the new value (123).

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

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

console.log(int32[0]); // 0;, 0, 123); 
Atomics.wake(int32, 0, 1);


Specification Status Comment
ECMAScript Shared Memory and Atomics
The definition of 'Atomics.wait' in that specification.
Draft Initial definition.

Browser compatibility

Feature Chrome Edge Firefox (Gecko) Internet Explorer Opera Safari
Basic support No support [2] No support 46 (46) [1] [3] No support No support No support
Feature Android Chrome for Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
Basic support No support No support 46.0 (46) [1] No support No support No support

[1] This feature is disabled by a preference setting. In about:config, set javascript.options.shared_memory to true

[2] The implementation is under development and needs these runtime flags: --js-flags=--harmony-sharedarraybuffer --enable-blink-feature=SharedArrayBuffer

[3] In versions 46 and 47, this method was named Atomics.futexWait() and the properties Atomics.OK, Atomics.TIMEDOUT, Atomics.NOTEQUAL were returned instead of the strings.

See also


© 2016 Mozilla Contributors
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.

Atomics Experimental JavaScript Method Shared Memory