Agreed. I'm still in the early learning stages but it has been pretty awesome so far.
Whelp. I'm horrible at these things but I'll give it a shot.
That is literally the first time that I've ever seen someone initialize 2 variables in a for...loop. Kudos. Very crafty.
.join() actually defaults to using a comma, .join(",") is actually what you are doing. Instead you will want to do .join("") to combine without any separator.
Using a little ES6 yo. https://jsfiddle.net/u6Lzgr7a/