CodeParkA WeakMap is a key-value collection that does not keep its keys alive. When nothing else references a key object, the garbage collector can free it, and its entry disappears too.
Keys: they must be objects, or non-registered symbols (symbols not created with Symbol.for). The map holds them weakly.
Limits: entries can disappear at any time. So a WeakMap cannot be looped over, has no size and has no clear. You can only use get, set, has and delete, with a key you already hold.
When to use it: to attach data to objects you do not own, without leaking memory. Examples:
- caching results per object, like memoizing a function with an object argument
- storing private data for class instances
- storing metadata for DOM nodes that should go away when the node is removed
A regular Map would keep those objects alive forever.
Related: WeakSet is the same idea for checking membership. WeakRef gives a weak reference to one single object.
WeakMapkeys are objects held weakly. Entries disappear when their keys are garbage collected.- A
WeakMapcannot be looped over and has nosize, because its contents depend on GC timing. - Use it for per-object caches, private data and DOM metadata.
- A normal
Mapwith object keys stops those objects from being collected.
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