Nope, totally readable to me; this is pretty much (I think) the standard way to populate a 2D array with specific values.

If you're using JS then you shouldn't be expecting to read for loops and C-like constructs all the time; that's why you're writing in JS and not C, right? (Just like in Ruby you abuse all the aliases because they're here :D)

Check to see if there's a space at the end of your returned string. This was an issue on a previous KATA, could be your issue as well. Also maybe you're supposed to return a float or int? Are you sure its supposed to be a string?

When I'm writing code that has to be maintained, I don't golf. I mean, seriously, even I can barely read this, and it wasn't that long ago.

I'd probably use something boring, like for loops. Lame.

If I was a developer working on a team with you I would pull out every single hair on my head trying to keep up.