Atomics.exchange()

BaselineWidely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since December 2021.

TheAtomics.exchange() static method exchanges 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 between the read of the old value and the write of the new value.

Try it

// Create a SharedArrayBuffer with a size in bytesconst buffer = new SharedArrayBuffer(16);const uint8 = new Uint8Array(buffer);uint8[0] = 5;console.log(Atomics.load(uint8, 0));// Expected output: 5Atomics.exchange(uint8, 0, 2); // Returns 5console.log(Atomics.load(uint8, 0));// Expected output: 2

Syntax

Atomics.exchange(typedArray, index, value)

Parameters

typedArray: An integer typed array. One ofInt8Array,Uint8Array,Int16Array,Uint16Array,Int32Array,Uint32Array,BigInt64Array, orBigUint64Array.
index: The position in thetypedArray to exchange avalue.
value: The number to exchange.

Return value

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

Exceptions

TypeError: Thrown iftypedArray is not one of the allowed integer types.
RangeError: Thrown ifindex is out of bounds in thetypedArray.

Examples

Using exchange()

const sab = new SharedArrayBuffer(1024);const ta = new Uint8Array(sab);Atomics.exchange(ta, 0, 12); // returns 0, the old valueAtomics.load(ta, 0); // 12