WeakMap

A WeakMap is a collection of key/value pairs whose keys must be objects or non-registered symbols, with values of any arbitrary JavaScript type, and which does not create strong references to its keys. That is, an object's presence as a key in a WeakMap does not prevent the object from being garbage collected. Once an object used as a key has been collected, its corresponding values in any WeakMap become candidates for garbage collection as well — as long as they aren't strongly referred to elsewhere. The only primitive type that can be used as a WeakMap key is symbol — more specifically, non-registered symbols — because non-registered symbols are guaranteed to be unique and cannot be re-created.

Safe to Use

Browsers

Servers

Version Breakdown

See Also

• Polyfill of WeakMap in core-js
• WeakMap object in the Keyed collections guide
• Hiding Implementation Details with ECMAScript 6 WeakMaps
• Map
• Set
• WeakSet

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