Atomics.add()

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 {{jsxref("Int8Array")}}, {{jsxref("Uint8Array")}}, {{jsxref("Int16Array")}}, {{jsxref("Uint16Array")}}, {{jsxref("Int32Array")}}, {{jsxref("Uint32Array")}}, {{jsxref("BigInt64Array")}}, or {{jsxref("BigUint64Array")}}.
• index
• : The position in the typedArray to add a value to.
• value
• : The number to add.

Return value#

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

Exceptions#

• {{jsxref("TypeError")}}
• : Thrown if typedArray is not one of the allowed integer types.
• {{jsxref("RangeError")}}
• : Thrown if index is out of bounds in the typedArray.

Examples#

Note that these examples cannot be run directly from the console or an arbitrary web page, because SharedArrayBuffer is not defined unless its security 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#

{{Specifications}}

Browser compatibility#

{{Compat}}

See also#

• {{jsxref("Atomics")}}
• {{jsxref("Atomics.sub()")}}