Web/JavaScript/Reference/Global objects/Atomics/wait

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

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

Syntax

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

Parameters

typedArray: A shared Int32Array.
index: The position in the typedArray to wait on.
value: 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".

Exceptions

Throws a TypeError, if typedArray is not a shared Int32Array.
Throws a RangeError, if index is out of bounds in the typedArray.

Examples

Using wait()

Given a shared Int32Array:

const sab = new SharedArrayBuffer(1024);
const 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 notified 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 notifies the waiting thread once it has written:

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

Specifications

Specification
ECMAScript (ECMA-262)The definition of 'Atomics.wait' in that specification.

Browser compatibility

Update compatibility data on GitHub

	Desktop						Mobile						Server
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet	Node.js
`wait`	Chrome Full support 68 Full support 68 No support 60 — 63 Notes' Notes' Chrome disabled `SharedArrayBuffer` on January 5, 2018 to help reduce the efficacy of speculative side-channel attacks. This was a temporary removal while mitigations were put in place.	Edge Full support 79 Full support 79 No support 16 — 17 Notes' Notes' Support was removed to mitigate speculative execution side-channel attacks (Windows blog).	Firefox Full support 78 Full support 78 Full support 57 Notes' Disabled' Notes' Support was disabled by default to mitigate speculative execution side-channel attacks (Mozilla Security Blog). Disabled' From version 57: this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config. No support 55 — 57 No support 48 — 55 Disabled' Disabled' From version 48 until version 55 (exclusive): this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config. No support 46 — 48 Notes' Alternate Name' Disabled' Notes' The method returns values `Atomics.OK`, `Atomics.TIMEDOUT`, and `Atomics.NOTEQUAL`, instead of the later-specified strings. Alternate Name' Uses the non-standard name: `futexWait` Disabled' From version 46 until version 48 (exclusive): this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config.	IE No support No	Opera No support No	Safari No support 10.1 — 11.1	WebView Android No support 60 — 63 Notes' No support 60 — 63 Notes' Notes' Chrome disabled `SharedArrayBuffer` on January 5, 2018 to help reduce the efficacy of speculative side-channel attacks. This is intended as a temporary measure until other mitigations are in place.	Chrome Android No support 60 — 63 Notes' No support 60 — 63 Notes' Notes' Chrome disabled `SharedArrayBuffer` on January 5, 2018 to help reduce the efficacy of speculative side-channel attacks. This is intended as a temporary measure until other mitigations are in place.	Firefox Android Full support 57 Notes' Disabled' Full support 57 Notes' Disabled' Notes' Support was disabled by default to mitigate speculative execution side-channel attacks (Mozilla Security Blog). Disabled' From version 57: this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config. No support 55 — 57 No support 48 — 55 Disabled' Disabled' From version 48 until version 55 (exclusive): this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config. No support 46 — 48 Notes' Alternate Name' Disabled' Notes' The method returns values `Atomics.OK`, `Atomics.TIMEDOUT`, and `Atomics.NOTEQUAL`, instead of the later-specified strings. Alternate Name' Uses the non-standard name: `futexWait` Disabled' From version 46 until version 48 (exclusive): this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config.	Opera Android No support No	Safari iOS No support 10.3 — 11.3	Samsung Internet Android No support No Notes' No support No Notes' Notes' Chrome disabled `SharedArrayBuffer` on January 5, 2018 to help reduce the efficacy of speculative side-channel attacks. This is intended as a temporary measure until other mitigations are in place.	nodejs Full support 8.10.0

Legend

Full support: Full support
No support: No support
See implementation notes.': See implementation notes.
User must explicitly enable this feature.': User must explicitly enable this feature.
Uses a non-standard name.': Uses a non-standard name.