Atomics.add()
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.add() staticmethod adds a given value at a given position in the array and returns the old value atthat position. This atomic operation guarantees that no other write happens until themodified value is written back.
Try it
// Create a SharedArrayBuffer with a size in bytesconst buffer = new SharedArrayBuffer(16);const uint8 = new Uint8Array(buffer);uint8[0] = 7;// 7 + 2 = 9console.log(Atomics.add(uint8, 0, 2));// Expected output: 7console.log(Atomics.load(uint8, 0));// Expected output: 9Syntax
js
Atomics.add(typedArray, index, value)Parameters
typedArrayAn integer typed array. One of
Int8Array,Uint8Array,Int16Array,Uint16Array,Int32Array,Uint32Array,BigInt64Array, orBigUint64Array.indexThe position in the
typedArrayto add avalueto.valueThe number to add.
Return value
The old value at the given position(typedArray[index]).
Exceptions
TypeErrorThrown if
typedArrayis not one of the allowed integer types.RangeErrorThrown if
indexis out of bounds in thetypedArray.
Examples
Using add()
js
const sab = new SharedArrayBuffer(1024);const ta = new Uint8Array(sab);Atomics.add(ta, 0, 12); // returns 0, the old valueAtomics.load(ta, 0); // 12Specifications
| Specification |
|---|
| ECMAScript® 2026 Language Specification # sec-atomics.add |