WeakMap and WeakSet

A good explanation of weakmap use case

WeakMap only has these instance methods:

WeakMap.prototype.delete()
WeakMap.prototype.get()
WeakMap.prototype.has()
WeakMap.prototype.set()

A weakmap can't tell how big it is, and can't keep order of keys like Object.

• Map/WeakMap/Object all can use object as key
• WeakMap can only use object as key
• WeakMap use weak reference, so the key will be garbage collected if the object is no longer in use. This can help prevent memory leak.