Trivial map/filter/reduce is not a novel kata idea.

Your example solution is regrettably imperative - which is entirely a matter of taste. :D I just like a more functional style.

It's also showcasing some Less-than-good Practices, such as inconsistent indentation and for .. in instead of for .. of.

See the fork. I suggest this is not what you want to be showcasing as an example solution.

IMO the spec is a bit ambiguous. It doesn't specify that special values such as null will be tested and doesn't specify that nested arrays and/or objects will not be passed in. Perhaps you could clarify in the Description a bit exactly what type of values the solver should expect to deal with in the array passed in? Cheers :)