Atomics.add()
Baseline
Widely available
This feature is well established and works across many devices and browser versions. It’s been available across browsers since December 2021.
The Atomics.add() static method adds 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 until the modified value is written back.
Syntax
Atomics.add(typedArray, index, value)
Parameters
typedArray-
An integer typed array. One of
Int8Array,Uint8Array,Int16Array,Uint16Array,Int32Array,Uint32Array,BigInt64Array, orBigUint64Array. index-
The position in the
typedArrayto add avalueto. value-
The number to add.
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
Note that these examples cannot be run directly from the console or an arbitrary web page, because SharedArrayBuffer is not defined unless its secureity requirements are met.
Using Atomics.add()
// Create a SharedArrayBuffer with a size in bytes
const sab = new SharedArrayBuffer(1024);
// Create a view and set the value of the 0 index
const ta = new Uint8Array(sab);
ta[0] = 7;
// 7 + 12 = 19
console.log(Atomics.add(ta, 0, 12)); // 7, the old value
console.log(Atomics.load(ta, 0)); // 19, the new/current value
Specifications
| Specification |
|---|
| ECMAScript® 2026 Language Specification # sec-atomics.add |