terrible test cases, as well as a description

Confusing description. And it definitely looks like 6

agreed. could be done in a single loop which would be a better practice

"accepting a native Array method is not working"
Failed on 5th test

additional counter "j" would be even faster )

very complicated solution (memory) for such a simple task

works just for short array. On very large it drops with - "RangeError: Maximum call stack size exceeded"

interesting solution. But for very big matrix it's a litlle bit slower than through traditional for-like and if. At least in Chrome

.replace is 3 to 15 times faster (Chrome). Just tested.

very very clever ;)

Tests for this cata makes me feel bad.

not bad ;)