Subverting control with weak references

In JavaScript we have two APIs to work with weak references: WeakMap and WeakRef. (Before I wrote this article I thought WeakRef was only a proposal, but it turns out most browsers have already implemented it) One of the more common use cases uses WeakMap. This data structure keeps a weak reference to the keys in the map, and a strong reference between the keys and values. I guess I should explain what a "weak reference" is: usually if you have a reference to an object in a variable, it stops the garbage collector from deleting it (which makes sense). It'd be weird if suddenly your variable pointed to nothing right?.