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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
A shared integer typed array. One of Int8Array, Uint8Array, Int16Array, Uint16Array, Int32Array, or Uint32Array.
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 TypeError, if typedArray is not a shared typed array type.
  • Throws a RangeError, if index is out of bounds in the typedArray.

Examples

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

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

Specifications

Specification Status Comment
ECMAScript Latest Draft (ECMA-262)
The definition of 'Atomics.add' in that specification.
Draft Initial definition in ES2017.

Browser compatibility

Feature Chrome Edge Firefox Internet Explorer Opera Safari
Basic support 601 No2

573 4

55 — 57

46 — 555

No No 10.1 —?
Feature Android webview Chrome for Android Edge mobile Firefox for Android Opera Android iOS Safari Samsung Internet
Basic support 601 601 ?

573 4

55 — 57

46 — 555

No No ?

1. 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.

2. Support was removed to mitigate speculative execution side-channel attacks (Windows blog).

3. Support was disabled by default to mitigate speculative execution side-channel attacks (Mozilla Security Blog).

4. 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.

5. 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.

See also

© 2005–2018 Mozilla Developer Network and individual contributors.
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Atomics/add