Sure they do. You just need to start thinking of javascript as a functional language and all this stuff becomes much ... simpler.

First of all, why would you even need to reason about a function's internal state? That's a sign of a leaky abstraction.

Furthermore, every time you want to manipulate the internal state of a function, what you're really after is defining a better API to provide arguments to said function.

And if you still for some reason need to dick around with a function's internal state, just use partial function application.