actually map itself has nothing to do with the repeat - it just passes the element's index to the callback function. the repetition is provided by repeat() getting the index in this specific case.

I guess you learn something new everyday lol, I had no idea you could add an incrementor to map(). I guess it's because map() is an iterative method, there's a couple of examples of an index being used with map() on the mdn, but it isn't explicitly stated anywhere else to my knowledge.