[stickupkid]

It does, but the map has a reference to it, so it will "leak" (in gc languages an unwanted reference is considered a leak). If this map got rather large, you could end up with a rather large heap and it would be un-obvious why at first.

[withinboredom]

Do Promises hold a reference to the chain of functions that end in the result? If so, that seems like a bug.

[epolanski]

A promise is just an object, it does not contain any reference to the chained functions.