Atomics.exchange

The static Atomics.exchange() 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 until the modified value is written back.

Syntax

Atomics.exchange(typedArray, index, value)

Parameters

typedArray

A shared integer typed array. One of Int8Array, Uint8Array, Int16Array, Uint16Array, Int32Array, or Uint32Array.

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

• Throws a TypeError, if typedArray is not one of the allowed integer types.
• Throws a TypeError, if typedArray is not a shared typed array type.
• Throws a RangeError, if index is out of bounds in the typedArray.

Examples

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

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

Specifications

Specification	Status	Comment
ECMAScript Shared Memory and Atomics The definition of 'Atomics.exchange' in that specification.	Draft	Initial definition.

Browser compatibility

[1] In Firefox version 46 until version 51, this feature was disabled by a preference setting. In about:config, set javascript.options.shared_memory to true.

[2] The implementation is under development and needs these runtime flags: --js-flags=--harmony-sharedarraybuffer --enable-blink-feature=SharedArrayBuffer

See also

• Atomics
• Atomics.compareExchange()