The static Atomics
.compareExchange()
method exchanges a given replacement value at a given position in the array, if a given expected value equals the old value. It returns the old value at that position whether it was equal to the expected value or not. This atomic operation guarantees that no other write happens until the modified value is written back.
Syntax
Atomics.compareExchange(typedArray, index, expectedValue, replacementValue)
Parameters
typedArray
- A shared integer typed array. One of
Int8Array
,Uint8Array
,Int16Array
,Uint16Array
,Int32Array
, orUint32Array
. index
- The position in the
typedArray
to exchange avalue
. expectedValue
- The value to check for equality.
- replacementValue
- The number to exchange.
Return value
The old value at the given position (typedArray[index]
).
Exceptions
- Throws a
TypeError
, iftypedArray
is not one of the allowed integer types. - Throws a
TypeError
, iftypedArray
is not a shared typed array type. - Throws a
RangeError
, ifindex
is out of bounds in thetypedArray
.
Examples
var sab = new SharedArrayBuffer(1024); var ta = new Uint8Array(sab); ta[0] = 7; Atomics.compareExchange(ta, 0, 7, 12); // returns 7, the old value Atomics.load(ta, 0); // 12
Specifications
Specification | Status | Comment |
---|---|---|
ECMAScript Latest Draft (ECMA-262) The definition of 'Atomics.compareExchange' in that specification. |
Living Standard | Initial definition in ES2017. |
Browser compatibility
Feature | Chrome | Edge | Firefox | Internet Explorer | Opera | Safari |
---|---|---|---|---|---|---|
Basic support | 60 | 16 | 55 46 — 541 | No | No | 10.1 |
Feature | Android webview | Chrome for Android | Edge mobile | Firefox for Android | IE mobile | Opera Android | iOS Safari |
---|---|---|---|---|---|---|---|
Basic support | 60 | 60 | ? | 55 46 — 541 | No | No | No |
1. From version 46 until version 54 (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.