Nope, they are not particularly well documented.

I find JS is well documented on MDN, but doc writers can't possibly imagine all edge cases and interactions. A lot of these cases are "If you knew about that simple feature of instruction A and the simple feature of instruction B and how they work together then you can solve this problem".

Oh. I actually clean forgot that MDN has docs on JS, not just DOM :)

Yes. You're correct about that