[danielnaab]

I've used a WeakMap for a kind of memoization.

Assume an immutable object may undergo an expensive transform that returns an object, which is then stored in a WeakMap keyed to the immutable. When there are no new references to that object, the garbage collector will clean it up, but otherwise the expensive transform may be avoided with a lookup on the WeakMap.

It provides a pretty nice way to decouple your caching from the rest of the codebase.