Web/JavaScript/Reference/Global objects/Atomics/add

The static Atomics.add() method adds a given value at a given position in the array and returns the old value at that position. This atomic operation guarantees that no other write happens until the modified value is written back.

Syntax

Atomics.add(typedArray, index, value)

Parameters

typedArray: An integer typed array. One of Int8Array, Uint8Array, Int16Array, Uint16Array, Int32Array, Uint32Array, BigInt64Array, or BigUint64Array.
index: The position in the typedArray to add a value to.
value: The number to add.

Return value

The old value at the given position (typedArray[index]).

Exceptions

Throws a TypeError, if typedArray is not one of the allowed integer types.
Throws a RangeError, if index is out of bounds in the typedArray.

Examples

Using add()

const sab = new SharedArrayBuffer(1024);
const ta = new Uint8Array(sab);

Atomics.add(ta, 0, 12); // returns 0, the old value
Atomics.load(ta, 0); // 12

Specifications

Specification
ECMAScript (ECMA-262)The definition of 'Atomics.add' 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
`add`	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 46 — 55 Disabled' Disabled' From version 46 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.	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 46 — 55 Disabled' Disabled' From version 46 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.	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.