I can't really reconcile wanting to avoid nested functions with what you did with NFEs and IIFEs.

That comment wasn't directed at you but at the person that voted this Best Practice. ( I sincerely hope that wasn't you. )

I actually like some of what you're doing, though un- and restructuring arr before map is quite unnecessary, renaming length to notEmpty is as well, and I can only hope Node is smart enough to reuse tails in `([a,...arr]).

that is typeScript.

The program uses flow (type checker) to write it.

to replicate it (Im assuming that is your question).

kindly switch to Babel and then type comment @flow and then follow up with your code.

Hope that helps.

For information on flow see : https://flow.org/

You tried to create some array of millions of elements or something like that (possibly infinite loop).

Oh you know, ... yet another cheating.