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I am trying to do the obvious thing with WeakMaps: I want to create a weak reference. In particular, I want to have a list of event-listeners without that list influencing the life of the listener.
So I was very excited to find WeakMaps, until I saw they were only built to satisfy one (fairly rare) use-case, extending objects that were otherwise sealed. I can't think when I ever wanted to do that, but I need lists of listeners all the time.
Is this possible to use WeakMaps in some clever way I haven't thought of to do this?
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WeakMap is Map -like collection that allows only objects as keys and removes them together with associated value once they become inaccessible by other means. WeakSet is Set -like collection that stores only objects and removes them once they become inaccessible by other means.
WeakSet in JavaScript is used to store a collection of objects. It adapts the same properties of that of a set i.e. does not store duplicates. The major difference of a WeakSet with the set is that a WeakSet is a collection of objects and not values of some particular type.
A WeakRef object contains a weak reference to an object, which is called its target or referent. A weak reference to an object is a reference that does not prevent the object from being reclaimed by the garbage collector. In contrast, a normal (or strong) reference keeps an object in memory.
Whenever you want to extend an object but can't because it is sealed - or from an external source - a WeakMap can be applied. A WeakMap is a map (dictionary) where the keys are weak - that is, if all references to the key are lost and there are no more references to the value - the value can be garbage collected.
No, it is impossible to use WeakMaps to create a weak reference. WeakMaps are not iterable, to use them you always need the key. This was a deliberate decision (also here), so that garbage collection does not influence the semantics of your program - which is exactly what you want.
Real weak references might come with ES8, see here and there for drafts.
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