Atomics

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Compatibility notes
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The Atomics object provides atomic operations as static methods. They are used with SharedArrayBuffer objects.

The Atomic operations are installed on an Atomics module. Unlike the other global objects, Atomics is not a constructor. You cannot use it with a new operator or invoke the Atomics object as a function. All properties and methods of Atomics are static (as is the case with the Math object, for example).

Properties

Atomics[Symbol.toStringTag]: The value of this property is "Atomics".

Methods

Atomic operations

When memory is shared, multiple threads can read and write the same data in memory. Atomic operations make sure that predictable values are written and read, that operations are finished before the next operation starts and that operations are not interrupted.

Atomics.add(): Adds the provided value to the existing value at the specified index of the array. Returns the old value at that index.
Atomics.and(): Computes a bitwise AND on the value at the specified index of the array with the provided value. Returns the old value at that index.
Atomics.compareExchange(): Stores a value at the specified index of the array, if it equals a value. Returns the old value.
Atomics.exchange(): Stores a value at the specified index of the array. Returns the old value.

Atomics.load(): Returns the value at the specified index of the array.
Atomics.or(): Computes a bitwise OR on the value at the specified index of the array with the provided value. Returns the old value at that index.
Atomics.store(): Stores a value at the specified index of the array. Returns the value.
Atomics.sub(): Subtracts a value at the specified index of the array. Returns the old value at that index.
Atomics.xor(): Computes a bitwise XOR on the value at the specified index of the array with the provided value. Returns the old value at that index.

Wait and wake

The wait() and wake() methods are modeled on Linux futexes ("fast user-space mutex") and provide ways for waiting until a certain condition becomes true and are typically used as blocking constructs.

Atomics.wait(): Verifies that the specified index of the array still contains a value and sleeps awaiting or times out. Returns either "ok", "not-equal", or "timed-out". If waiting is not allowed in the calling agent then it throws an Error exception (most browsers will not allow wait() on the browser's main thread).
Atomics.wake(): Wakes up agents that are waiting on the specified index of the array. Returns the number of agents that were woken up.
Atomics.isLockFree(size): An optimization primitive that can be used to determine whether to use locks or atomic operations. Returns true, if an atomic operation on arrays of the given element size will be implemented using a hardware atomic operation (as opposed to a lock). Experts only.

Specifications

Specification	Status	Comment
ECMAScript Latest Draft (ECMA-262) The definition of 'Atomics' in that specification.	Draft	Initial definition in ES2017.
ECMAScript 2017 (ECMA-262) The definition of 'Atomics' in that specification.	Standard

Feature	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari
Basic support	68 60 — 63²	No³	57⁴ ⁵ 55 — 57 46 — 55⁶	No	No	10.1 —?
`add`	68 60 — 63²	16³	57⁴ ⁵ 55 — 57 46 — 55⁶	No	No	10.1 —?
`and`	68 60 — 63²	16³	57⁴ ⁵ 55 — 57 46 — 55⁶	No	No	10.1 —?
`compareExchange`	68 60 — 63²	16³	57⁴ ⁵ 55 — 57 46 — 55⁶	No	No	10.1 —?
`exchange`	68 60 — 63²	16³	57⁴ ⁵ 55 — 57 46 — 55⁶	No	No	10.1 —?
`isLockFree`	68 60 — 63²	16³	57⁴ ⁵ 55 — 57 46 — 55⁶	No	No	10.1 —?
`load`	68 60 — 63²	16³	57⁴ ⁵ 55 — 57 46 — 55⁶	No	No	10.1 —?
`or`	68 60 — 63²	16³	57⁴ ⁵ 55 — 57 46 — 55⁶	No	No	10.1 —?
`store`	68 60 — 63²	16³	57⁴ ⁵ 55 — 57 46 — 55⁶	No	No	10.1 —?
`sub`	68 60 — 63²	16³	57⁴ ⁵ 55 — 57 46 — 55⁶	No	No	10.1 —?
`wait`	68 60 — 63²	16³	57⁴ ⁵ 55 — 57 48 — 55⁷ 46 — 48¹⁰ ⁸ ⁹	No	No	10.1 —?
`wake`	68 60 — 63²	16³	57⁴ ⁵ 55 — 57 48 — 55⁷ 46 — 48¹¹ ¹² ⁹	No	No	10.1 —?
`xor`	68 60 — 63²	16³	57⁴ ⁵ 55 — 57 46 — 55⁶	No	No	10.1 —?

Feature	Android webview	Chrome for Android	Edge mobile	Firefox for Android	Opera Android	iOS Safari	Samsung Internet
Basic support	60 — 63¹	60 — 63¹	?	57⁴ ⁵ 55 — 57 46 — 55⁶	No	No	No
`add`	60 — 63¹	60 — 63¹	?	57⁴ ⁵ 55 — 57 46 — 55⁶	No	No	No
`and`	60 — 63¹	60 — 63¹	?	57⁴ ⁵ 55 — 57 46 — 55⁶	No	No	No
`compareExchange`	60 — 63¹	60 — 63¹	?	57⁴ ⁵ 55 — 57 46 — 55⁶	No	No	No
`exchange`	60 — 63¹	60 — 63¹	?	57⁴ ⁵ 55 — 57 46 — 55⁶	No	No	No
`isLockFree`	60 — 63¹	60 — 63¹	?	57⁴ ⁵ 55 — 57 46 — 55⁶	No	No	No
`load`	60 — 63¹	60 — 63¹	?	57⁴ ⁵ 55 — 57 46 — 55⁶	No	No	No
`or`	60 — 63¹	60 — 63¹	?	57⁴ ⁵ 55 — 57 46 — 55⁶	No	No	No
`store`	60 — 63¹	60 — 63¹	?	57⁴ ⁵ 55 — 57 46 — 55⁶	No	No	No
`sub`	60 — 63¹	60 — 63¹	?	57⁴ ⁵ 55 — 57 46 — 55⁶	No	No	No
`wait`	60 — 63¹	60 — 63¹	?	57⁴ ⁵ 55 — 57 48 — 55⁷ 46 — 48¹⁰ ⁸ ⁹	No	No	No
`wake`	60 — 63¹	60 — 63¹	?	57⁴ ⁵ 55 — 57 48 — 55⁷ 46 — 48¹¹ ¹² ⁹	No	No	No
`xor`	60 — 63¹	60 — 63¹	?	57⁴ ⁵ 55 — 57 46 — 55⁶	No	No	No

1. Chrome disabled SharedArrayBuffer on January 5, 2018 to help reduce the efficacy of speculative side-channel attacks. This is intended as a temporary measure until other mitigations are in place.

2. Chrome disabled SharedArrayBuffer on January 5, 2018 to help reduce the efficacy of speculative side-channel attacks. This was a temporary removal while mitigations were put in place.

3. Support was removed to mitigate speculative execution side-channel attacks (Windows blog).

4. Support was disabled by default to mitigate speculative execution side-channel attacks (Mozilla Security Blog).

5. From version 57: this feature is behind the javascript.options.shared_memory preference (needs to be set to true). To change preferences in Firefox, visit about:config.

6. From version 46 until version 55 (exclusive): this feature is behind the javascript.options.shared_memory preference (needs to be set to true). To change preferences in Firefox, visit about:config.

7. From version 48 until version 55 (exclusive): this feature is behind the javascript.options.shared_memory preference (needs to be set to true). To change preferences in Firefox, visit about:config.

8. The method returns values Atomics.OK, Atomics.TIMEDOUT, and Atomics.NOTEQUAL, instead of the later-specified strings.

9. From version 46 until version 48 (exclusive): this feature is behind the javascript.options.shared_memory preference (needs to be set to true). To change preferences in Firefox, visit about:config.

10. Supported as futexWait.

11. The count parameter defaults to 0 instead of the later-specified +Infinity.

12. Supported as futexWake.

	Desktop						Mobile							Server
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Edge Mobile	Firefox for Android	Opera for Android	iOS Safari	Samsung Internet	Node.js
Basic support	Full support 68 Full support 68 No support 60 — 63 Notes Notes Chrome disabled SharedArrayBuffer on January 5, 2018 to help reduce the efficacy of speculative side-channel attacks. This was a temporary removal while mitigations were put in place.	No support No Notes No support No Notes Notes Support was removed to mitigate speculative execution side-channel attacks (Windows blog).	Full support 57 Notes Disabled Full support 57 Notes Disabled Notes Support was disabled by default to mitigate speculative execution side-channel attacks (Mozilla Security Blog). Disabled From version 57: this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config. No support 55 — 57 No support 46 — 55 Disabled Disabled From version 46 until version 55 (exclusive): this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config.	No support No	No support No	No support 10.1 — ?	No support 60 — 63 Notes No support 60 — 63 Notes Notes Chrome disabled SharedArrayBuffer on January 5, 2018 to help reduce the efficacy of speculative side-channel attacks. This is intended as a temporary measure until other mitigations are in place.	No support 60 — 63 Notes No support 60 — 63 Notes Notes Chrome disabled SharedArrayBuffer on January 5, 2018 to help reduce the efficacy of speculative side-channel attacks. This is intended as a temporary measure until other mitigations are in place.	?	Full support 57 Notes Disabled Full support 57 Notes Disabled Notes Support was disabled by default to mitigate speculative execution side-channel attacks (Mozilla Security Blog). Disabled From version 57: this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config. No support 55 — 57 No support 46 — 55 Disabled Disabled From version 46 until version 55 (exclusive): this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config.	No support No	No support No	No support No	No support No
`add`	Full support 68 Full support 68 No support 60 — 63 Notes Notes Chrome disabled SharedArrayBuffer on January 5, 2018 to help reduce the efficacy of speculative side-channel attacks. This was a temporary removal while mitigations were put in place.	Full support 16 Notes Full support 16 Notes Notes Support was removed to mitigate speculative execution side-channel attacks (Windows blog).	Full support 57 Notes Disabled Full support 57 Notes Disabled Notes Support was disabled by default to mitigate speculative execution side-channel attacks (Mozilla Security Blog). Disabled From version 57: this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config. No support 55 — 57 No support 46 — 55 Disabled Disabled From version 46 until version 55 (exclusive): this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config.	No support No	No support No	No support 10.1 — ?	No support 60 — 63 Notes No support 60 — 63 Notes Notes Chrome disabled SharedArrayBuffer on January 5, 2018 to help reduce the efficacy of speculative side-channel attacks. This is intended as a temporary measure until other mitigations are in place.	No support 60 — 63 Notes No support 60 — 63 Notes Notes Chrome disabled SharedArrayBuffer on January 5, 2018 to help reduce the efficacy of speculative side-channel attacks. This is intended as a temporary measure until other mitigations are in place.	?	Full support 57 Notes Disabled Full support 57 Notes Disabled Notes Support was disabled by default to mitigate speculative execution side-channel attacks (Mozilla Security Blog). Disabled From version 57: this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config. No support 55 — 57 No support 46 — 55 Disabled Disabled From version 46 until version 55 (exclusive): this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config.	No support No	No support No	No support No	Full support 8.10.0
`and`	Full support 68 Full support 68 No support 60 — 63 Notes Notes Chrome disabled SharedArrayBuffer on January 5, 2018 to help reduce the efficacy of speculative side-channel attacks. This was a temporary removal while mitigations were put in place.	Full support 16 Notes Full support 16 Notes Notes Support was removed to mitigate speculative execution side-channel attacks (Windows blog).	Full support 57 Notes Disabled Full support 57 Notes Disabled Notes Support was disabled by default to mitigate speculative execution side-channel attacks (Mozilla Security Blog). Disabled From version 57: this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config. No support 55 — 57 No support 46 — 55 Disabled Disabled From version 46 until version 55 (exclusive): this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config.	No support No	No support No	No support 10.1 — ?	No support 60 — 63 Notes No support 60 — 63 Notes Notes Chrome disabled SharedArrayBuffer on January 5, 2018 to help reduce the efficacy of speculative side-channel attacks. This is intended as a temporary measure until other mitigations are in place.	No support 60 — 63 Notes No support 60 — 63 Notes Notes Chrome disabled SharedArrayBuffer on January 5, 2018 to help reduce the efficacy of speculative side-channel attacks. This is intended as a temporary measure until other mitigations are in place.	?	Full support 57 Notes Disabled Full support 57 Notes Disabled Notes Support was disabled by default to mitigate speculative execution side-channel attacks (Mozilla Security Blog). Disabled From version 57: this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config. No support 55 — 57 No support 46 — 55 Disabled Disabled From version 46 until version 55 (exclusive): this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config.	No support No	No support No	No support No	Full support 8.10.0
`compareExchange`	Full support 68 Full support 68 No support 60 — 63 Notes Notes Chrome disabled SharedArrayBuffer on January 5, 2018 to help reduce the efficacy of speculative side-channel attacks. This was a temporary removal while mitigations were put in place.	Full support 16 Notes Full support 16 Notes Notes Support was removed to mitigate speculative execution side-channel attacks (Windows blog).	Full support 57 Notes Disabled Full support 57 Notes Disabled Notes Support was disabled by default to mitigate speculative execution side-channel attacks (Mozilla Security Blog). Disabled From version 57: this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config. No support 55 — 57 No support 46 — 55 Disabled Disabled From version 46 until version 55 (exclusive): this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config.	No support No	No support No	No support 10.1 — ?	No support 60 — 63 Notes No support 60 — 63 Notes Notes Chrome disabled SharedArrayBuffer on January 5, 2018 to help reduce the efficacy of speculative side-channel attacks. This is intended as a temporary measure until other mitigations are in place.	No support 60 — 63 Notes No support 60 — 63 Notes Notes Chrome disabled SharedArrayBuffer on January 5, 2018 to help reduce the efficacy of speculative side-channel attacks. This is intended as a temporary measure until other mitigations are in place.	?	Full support 57 Notes Disabled Full support 57 Notes Disabled Notes Support was disabled by default to mitigate speculative execution side-channel attacks (Mozilla Security Blog). Disabled From version 57: this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config. No support 55 — 57 No support 46 — 55 Disabled Disabled From version 46 until version 55 (exclusive): this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config.	No support No	No support No	No support No	Full support 8.10.0
`exchange`	Full support 68 Full support 68 No support 60 — 63 Notes Notes Chrome disabled SharedArrayBuffer on January 5, 2018 to help reduce the efficacy of speculative side-channel attacks. This was a temporary removal while mitigations were put in place.	Full support 16 Notes Full support 16 Notes Notes Support was removed to mitigate speculative execution side-channel attacks (Windows blog).	Full support 57 Notes Disabled Full support 57 Notes Disabled Notes Support was disabled by default to mitigate speculative execution side-channel attacks (Mozilla Security Blog). Disabled From version 57: this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config. No support 55 — 57 No support 46 — 55 Disabled Disabled From version 46 until version 55 (exclusive): this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config.	No support No	No support No	No support 10.1 — ?	No support 60 — 63 Notes No support 60 — 63 Notes Notes Chrome disabled SharedArrayBuffer on January 5, 2018 to help reduce the efficacy of speculative side-channel attacks. This is intended as a temporary measure until other mitigations are in place.	No support 60 — 63 Notes No support 60 — 63 Notes Notes Chrome disabled SharedArrayBuffer on January 5, 2018 to help reduce the efficacy of speculative side-channel attacks. This is intended as a temporary measure until other mitigations are in place.	?	Full support 57 Notes Disabled Full support 57 Notes Disabled Notes Support was disabled by default to mitigate speculative execution side-channel attacks (Mozilla Security Blog). Disabled From version 57: this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config. No support 55 — 57 No support 46 — 55 Disabled Disabled From version 46 until version 55 (exclusive): this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config.	No support No	No support No	No support No	Full support 8.10.0
`isLockFree`	Full support 68 Full support 68 No support 60 — 63 Notes Notes Chrome disabled SharedArrayBuffer on January 5, 2018 to help reduce the efficacy of speculative side-channel attacks. This was a temporary removal while mitigations were put in place.	Full support 16 Notes Full support 16 Notes Notes Support was removed to mitigate speculative execution side-channel attacks (Windows blog).	Full support 57 Notes Disabled Full support 57 Notes Disabled Notes Support was disabled by default to mitigate speculative execution side-channel attacks (Mozilla Security Blog). Disabled From version 57: this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config. No support 55 — 57 No support 46 — 55 Disabled Disabled From version 46 until version 55 (exclusive): this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config.	No support No	No support No	No support 10.1 — ?	No support 60 — 63 Notes No support 60 — 63 Notes Notes Chrome disabled SharedArrayBuffer on January 5, 2018 to help reduce the efficacy of speculative side-channel attacks. This is intended as a temporary measure until other mitigations are in place.	No support 60 — 63 Notes No support 60 — 63 Notes Notes Chrome disabled SharedArrayBuffer on January 5, 2018 to help reduce the efficacy of speculative side-channel attacks. This is intended as a temporary measure until other mitigations are in place.	?	Full support 57 Notes Disabled Full support 57 Notes Disabled Notes Support was disabled by default to mitigate speculative execution side-channel attacks (Mozilla Security Blog). Disabled From version 57: this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config. No support 55 — 57 No support 46 — 55 Disabled Disabled From version 46 until version 55 (exclusive): this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config.	No support No	No support No	No support No	Full support 8.10.0
`load`	Full support 68 Full support 68 No support 60 — 63 Notes Notes Chrome disabled SharedArrayBuffer on January 5, 2018 to help reduce the efficacy of speculative side-channel attacks. This was a temporary removal while mitigations were put in place.	Full support 16 Notes Full support 16 Notes Notes Support was removed to mitigate speculative execution side-channel attacks (Windows blog).	Full support 57 Notes Disabled Full support 57 Notes Disabled Notes Support was disabled by default to mitigate speculative execution side-channel attacks (Mozilla Security Blog). Disabled From version 57: this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config. No support 55 — 57 No support 46 — 55 Disabled Disabled From version 46 until version 55 (exclusive): this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config.	No support No	No support No	No support 10.1 — ?	No support 60 — 63 Notes No support 60 — 63 Notes Notes Chrome disabled SharedArrayBuffer on January 5, 2018 to help reduce the efficacy of speculative side-channel attacks. This is intended as a temporary measure until other mitigations are in place.	No support 60 — 63 Notes No support 60 — 63 Notes Notes Chrome disabled SharedArrayBuffer on January 5, 2018 to help reduce the efficacy of speculative side-channel attacks. This is intended as a temporary measure until other mitigations are in place.	?	Full support 57 Notes Disabled Full support 57 Notes Disabled Notes Support was disabled by default to mitigate speculative execution side-channel attacks (Mozilla Security Blog). Disabled From version 57: this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config. No support 55 — 57 No support 46 — 55 Disabled Disabled From version 46 until version 55 (exclusive): this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config.	No support No	No support No	No support No	Full support 8.10.0
`or`	Full support 68 Full support 68 No support 60 — 63 Notes Notes Chrome disabled SharedArrayBuffer on January 5, 2018 to help reduce the efficacy of speculative side-channel attacks. This was a temporary removal while mitigations were put in place.	Full support 16 Notes Full support 16 Notes Notes Support was removed to mitigate speculative execution side-channel attacks (Windows blog).	Full support 57 Notes Disabled Full support 57 Notes Disabled Notes Support was disabled by default to mitigate speculative execution side-channel attacks (Mozilla Security Blog). Disabled From version 57: this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config. No support 55 — 57 No support 46 — 55 Disabled Disabled From version 46 until version 55 (exclusive): this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config.	No support No	No support No	No support 10.1 — ?	No support 60 — 63 Notes No support 60 — 63 Notes Notes Chrome disabled SharedArrayBuffer on January 5, 2018 to help reduce the efficacy of speculative side-channel attacks. This is intended as a temporary measure until other mitigations are in place.	No support 60 — 63 Notes No support 60 — 63 Notes Notes Chrome disabled SharedArrayBuffer on January 5, 2018 to help reduce the efficacy of speculative side-channel attacks. This is intended as a temporary measure until other mitigations are in place.	?	Full support 57 Notes Disabled Full support 57 Notes Disabled Notes Support was disabled by default to mitigate speculative execution side-channel attacks (Mozilla Security Blog). Disabled From version 57: this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config. No support 55 — 57 No support 46 — 55 Disabled Disabled From version 46 until version 55 (exclusive): this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config.	No support No	No support No	No support No	Full support 8.10.0
`store`	Full support 68 Full support 68 No support 60 — 63 Notes Notes Chrome disabled SharedArrayBuffer on January 5, 2018 to help reduce the efficacy of speculative side-channel attacks. This was a temporary removal while mitigations were put in place.	Full support 16 Notes Full support 16 Notes Notes Support was removed to mitigate speculative execution side-channel attacks (Windows blog).	Full support 57 Notes Disabled Full support 57 Notes Disabled Notes Support was disabled by default to mitigate speculative execution side-channel attacks (Mozilla Security Blog). Disabled From version 57: this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config. No support 55 — 57 No support 46 — 55 Disabled Disabled From version 46 until version 55 (exclusive): this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config.	No support No	No support No	No support 10.1 — ?	No support 60 — 63 Notes No support 60 — 63 Notes Notes Chrome disabled SharedArrayBuffer on January 5, 2018 to help reduce the efficacy of speculative side-channel attacks. This is intended as a temporary measure until other mitigations are in place.	No support 60 — 63 Notes No support 60 — 63 Notes Notes Chrome disabled SharedArrayBuffer on January 5, 2018 to help reduce the efficacy of speculative side-channel attacks. This is intended as a temporary measure until other mitigations are in place.	?	Full support 57 Notes Disabled Full support 57 Notes Disabled Notes Support was disabled by default to mitigate speculative execution side-channel attacks (Mozilla Security Blog). Disabled From version 57: this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config. No support 55 — 57 No support 46 — 55 Disabled Disabled From version 46 until version 55 (exclusive): this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config.	No support No	No support No	No support No	Full support 8.10.0
`sub`	Full support 68 Full support 68 No support 60 — 63 Notes Notes Chrome disabled SharedArrayBuffer on January 5, 2018 to help reduce the efficacy of speculative side-channel attacks. This was a temporary removal while mitigations were put in place.	Full support 16 Notes Full support 16 Notes Notes Support was removed to mitigate speculative execution side-channel attacks (Windows blog).	Full support 57 Notes Disabled Full support 57 Notes Disabled Notes Support was disabled by default to mitigate speculative execution side-channel attacks (Mozilla Security Blog). Disabled From version 57: this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config. No support 55 — 57 No support 46 — 55 Disabled Disabled From version 46 until version 55 (exclusive): this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config.	No support No	No support No	No support 10.1 — ?	No support 60 — 63 Notes No support 60 — 63 Notes Notes Chrome disabled SharedArrayBuffer on January 5, 2018 to help reduce the efficacy of speculative side-channel attacks. This is intended as a temporary measure until other mitigations are in place.	No support 60 — 63 Notes No support 60 — 63 Notes Notes Chrome disabled SharedArrayBuffer on January 5, 2018 to help reduce the efficacy of speculative side-channel attacks. This is intended as a temporary measure until other mitigations are in place.	?	Full support 57 Notes Disabled Full support 57 Notes Disabled Notes Support was disabled by default to mitigate speculative execution side-channel attacks (Mozilla Security Blog). Disabled From version 57: this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config. No support 55 — 57 No support 46 — 55 Disabled Disabled From version 46 until version 55 (exclusive): this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config.	No support No	No support No	No support No	Full support 8.10.0
`wait`	Full support 68 Full support 68 No support 60 — 63 Notes Notes Chrome disabled SharedArrayBuffer on January 5, 2018 to help reduce the efficacy of speculative side-channel attacks. This was a temporary removal while mitigations were put in place.	Full support 16 Notes Full support 16 Notes Notes Support was removed to mitigate speculative execution side-channel attacks (Windows blog).	Full support 57 Notes Disabled Full support 57 Notes Disabled Notes Support was disabled by default to mitigate speculative execution side-channel attacks (Mozilla Security Blog). Disabled From version 57: this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config. No support 55 — 57 No support 48 — 55 Disabled Disabled From version 48 until version 55 (exclusive): this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config. No support 46 — 48 Notes Alternate Name Disabled Notes The method returns values `Atomics.OK`, `Atomics.TIMEDOUT`, and `Atomics.NOTEQUAL`, instead of the later-specified strings. Alternate Name Uses the non-standard name: `futexWait` Disabled From version 46 until version 48 (exclusive): this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config.	No support No	No support No	No support 10.1 — ?	No support 60 — 63 Notes No support 60 — 63 Notes Notes Chrome disabled SharedArrayBuffer on January 5, 2018 to help reduce the efficacy of speculative side-channel attacks. This is intended as a temporary measure until other mitigations are in place.	No support 60 — 63 Notes No support 60 — 63 Notes Notes Chrome disabled SharedArrayBuffer on January 5, 2018 to help reduce the efficacy of speculative side-channel attacks. This is intended as a temporary measure until other mitigations are in place.	?	Full support 57 Notes Disabled Full support 57 Notes Disabled Notes Support was disabled by default to mitigate speculative execution side-channel attacks (Mozilla Security Blog). Disabled From version 57: this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config. No support 55 — 57 No support 48 — 55 Disabled Disabled From version 48 until version 55 (exclusive): this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config. No support 46 — 48 Notes Alternate Name Disabled Notes The method returns values `Atomics.OK`, `Atomics.TIMEDOUT`, and `Atomics.NOTEQUAL`, instead of the later-specified strings. Alternate Name Uses the non-standard name: `futexWait` Disabled From version 46 until version 48 (exclusive): this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config.	No support No	No support No	No support No	Full support 8.10.0
`wake`	Full support 68 Full support 68 No support 60 — 63 Notes Notes Chrome disabled SharedArrayBuffer on January 5, 2018 to help reduce the efficacy of speculative side-channel attacks. This was a temporary removal while mitigations were put in place.	Full support 16 Notes Full support 16 Notes Notes Support was removed to mitigate speculative execution side-channel attacks (Windows blog).	Full support 57 Notes Disabled Full support 57 Notes Disabled Notes Support was disabled by default to mitigate speculative execution side-channel attacks (Mozilla Security Blog). Disabled From version 57: this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config. No support 55 — 57 No support 48 — 55 Disabled Disabled From version 48 until version 55 (exclusive): this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config. No support 46 — 48 Notes Alternate Name Disabled Notes The `count` parameter defaults to `0` instead of the later-specified `+Infinity`. Alternate Name Uses the non-standard name: `futexWake` Disabled From version 46 until version 48 (exclusive): this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config.	No support No	No support No	No support 10.1 — ?	No support 60 — 63 Notes No support 60 — 63 Notes Notes Chrome disabled SharedArrayBuffer on January 5, 2018 to help reduce the efficacy of speculative side-channel attacks. This is intended as a temporary measure until other mitigations are in place.	No support 60 — 63 Notes No support 60 — 63 Notes Notes Chrome disabled SharedArrayBuffer on January 5, 2018 to help reduce the efficacy of speculative side-channel attacks. This is intended as a temporary measure until other mitigations are in place.	?	Full support 57 Notes Disabled Full support 57 Notes Disabled Notes Support was disabled by default to mitigate speculative execution side-channel attacks (Mozilla Security Blog). Disabled From version 57: this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config. No support 55 — 57 No support 48 — 55 Disabled Disabled From version 48 until version 55 (exclusive): this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config. No support 46 — 48 Notes Alternate Name Disabled Notes The `count` parameter defaults to `0` instead of the later-specified `+Infinity`. Alternate Name Uses the non-standard name: `futexWake` Disabled From version 46 until version 48 (exclusive): this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config.	No support No	No support No	No support No	Full support 8.10.0
`xor`	Full support 68 Full support 68 No support 60 — 63 Notes Notes Chrome disabled SharedArrayBuffer on January 5, 2018 to help reduce the efficacy of speculative side-channel attacks. This was a temporary removal while mitigations were put in place.	Full support 16 Notes Full support 16 Notes Notes Support was removed to mitigate speculative execution side-channel attacks (Windows blog).	Full support 57 Notes Disabled Full support 57 Notes Disabled Notes Support was disabled by default to mitigate speculative execution side-channel attacks (Mozilla Security Blog). Disabled From version 57: this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config. No support 55 — 57 No support 46 — 55 Disabled Disabled From version 46 until version 55 (exclusive): this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config.	No support No	No support No	No support 10.1 — ?	No support 60 — 63 Notes No support 60 — 63 Notes Notes Chrome disabled SharedArrayBuffer on January 5, 2018 to help reduce the efficacy of speculative side-channel attacks. This is intended as a temporary measure until other mitigations are in place.	No support 60 — 63 Notes No support 60 — 63 Notes Notes Chrome disabled SharedArrayBuffer on January 5, 2018 to help reduce the efficacy of speculative side-channel attacks. This is intended as a temporary measure until other mitigations are in place.	?	Full support 57 Notes Disabled Full support 57 Notes Disabled Notes Support was disabled by default to mitigate speculative execution side-channel attacks (Mozilla Security Blog). Disabled From version 57: this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config. No support 55 — 57 No support 46 — 55 Disabled Disabled From version 46 until version 55 (exclusive): this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config.	No support No	No support No	No support No	Full support 8.10.0

Legend

Full support: Full support
No support: No support
Compatibility unknown: Compatibility unknown
See implementation notes.: See implementation notes.
User must explicitly enable this feature.: User must explicitly enable this feature.
Uses a non-standard name.: Uses a non-standard name.

Compatibility notes

Prior to Firefox 48, the latest API names and semantics weren't implemented yet. The changes between Firefox version 46 and version 48 are:

The methods Atomics.futexWakeOrRequeue() and Atomics.fence() are now removed entirely (bug 1259544 and bug 1225028).
The methods Atomics.wait() and Atomics.wake() were named Atomics.futexWait() and Atomics.futexWake() (bug 1260910). Note: The old names have been removed in version 49 and later (bug 1262062).
The properties Atomics.OK, Atomics.TIMEDOUT, Atomics.NOTEQUAL have been removed. The Atomics.wait() method now returns the strings "ok", "timed-out" and "not-equal" (bug 1260835).
The count parameter of the Atomics.wake() method has been changed: it now defaults to +Infinity, not 0 (bug 1253350).

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Contributors to this page: rwaldron, fscholz, mgthomas99, PatrickKettner, ryanmurakami, jameshkramer, erikadoyle, keffidesign, Satya_Achanta, Kaku, lth, Sheppy

Last updated by: rwaldron, Apr 26, 2018, 7:46:30 AM