Great solution

but quadratic in the number of copies of the resultant strings that are made. not best practice.

I don't comprehend this solution. Can someone explain how it works? Particularly what's being fed to accumulator...?

Does anyone else get uncomfortable relying on the fact that JS out-of-bounds array access is undefined instead of error-throwing for a kata or is that just me.

very clever solution, though a little problem. since there is no initial value been passed, the current index will start from 1 and never become 0.

O(n) in time complexity as well. +1

This is how I initially intended to code it, but I couldn't figure out how to code it, so I went with a more naive approach. Good job.

This is my favorite solution I've seen thus far. Very nice and understandable implementation. Clever!