WeakSets are a collection of Objects where each object can only appear once in the set similar to Set. Unlike Set, WeakSet does not allow iterating over its values. If WeakSet would be the only object holding on to the value, the value will be released from memory. The values stored in WeakSet cannot be primitive values (Boolean, Number, String, or undefined).
value is already stored, there is no change to the WeakSet. Returns
value was in
this before deleting it.