Atomics.compareExchange()
The Atomics.compareExchange() static 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.
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Syntax
Atomics.compareExchange(typedArray, index, expectedValue, replacementValue)
Parameters
typedArray-
An integer typed array. One of
Int8Array,Uint8Array,Int16Array,Uint16Array,Int32Array,Uint32Array,BigInt64Array, orBigUint64Array. index-
The position in the
typedArrayto exchange areplacementValue. expectedValue-
The value to check for equality.
replacementValue-
The number to exchange.
Return value
The old value at the given position (typedArray[index]).
Exceptions
TypeError-
Thrown if
typedArrayis not one of the allowed integer types. RangeError-
Thrown if
indexis out of bounds in thetypedArray.
Examples
Using compareExchange()
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
Specifications
| Specification |
|---|
| ECMAScript Language Specification # sec-atomics.compareexchange |
Browser compatibility
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