files/en-us/web/javascript/reference/global_objects/atomics/exchange/index.md

metadata

title: Atomics.exchange()
short-title: exchange()
slug: Web/JavaScript/Reference/Global_Objects/Atomics/exchange
page-type: javascript-static-method
browser-compat: javascript.builtins.Atomics.exchange
sidebar: jsref

The Atomics.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.

{{InteractiveExample("JavaScript Demo: Atomics.exchange()")}}

// Create a SharedArrayBuffer with a size in bytes
const buffer = new SharedArrayBuffer(16);
const uint8 = new Uint8Array(buffer);
uint8[0] = 5;

console.log(Atomics.load(uint8, 0));
// Expected output: 5

Atomics.exchange(uint8, 0, 2); // Returns 5
console.log(Atomics.load(uint8, 0));
// Expected output: 2

Syntax

Atomics.exchange(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 exchange a value.
• value
  • : The number to exchange.

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

Using exchange()

const sab = new SharedArrayBuffer(1024);
const ta = new Uint8Array(sab);

Atomics.exchange(ta, 0, 12); // returns 0, the old value
Atomics.load(ta, 0); // 12

Specifications

{{Specifications}}

Browser compatibility

{{Compat}}

See also

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