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.
Atomics.compareExchange(typedArray, index, expectedValue, replacementValue)
typedArray
An integer typed array. One of Int8Array
, Uint8Array
, Int16Array
, Uint16Array
, Int32Array
, Uint32Array
, BigInt64Array
, or BigUint64Array
.
index
The position in the typedArray
to exchange a value
.
expectedValue
The value to check for equality.
replacementValue
The number to exchange.
The old value at the given position (typedArray[index]
).
TypeError
, if typedArray
is not one of the allowed integer types. RangeError
, if index
is out of bounds in the typedArray
. const sab = new SharedArrayBuffer(1024); const ta = new Uint8Array(sab); ta[0] = 7; Atomics.compareExchange(ta, 0, 7, 12); // returns 7, the old value Atomics.load(ta, 0); // 12
Desktop | Mobile | Server | ||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Chrome | Edge | Firefox | Internet Explorer | Opera | Safari | WebView Android | Chrome Android | Firefox for Android | Opera Android | Safari on IOS | Samsung Internet | Deno | Node.js | |
compareExchange |
68
60-63
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. |
79
16-17
Support was removed to mitigate speculative execution side-channel attacks (Windows blog).
|
78
57
Support was disabled by default to mitigate speculative execution side-channel attacks (Mozilla Security Blog).
55-57
46-55
|
No |
No |
10.1-11.1 |
60-63
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. |
60-63
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. |
57
Support was disabled by default to mitigate speculative execution side-channel attacks (Mozilla Security Blog).
55-57
46-55
|
No |
10.3-11.3 |
No
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. |
1.0 |
8.10.0 |
© 2005–2021 MDN 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/compareExchange