agree!

Well, it certainly isn't best practice.

First point is correct but your second point is wrong. Becuase zero is falsy as well your suggested filter function would drop 0 from the result and fail when the first letter is upper case.

cool

Use single quotes unless string interpolation is required.

great solution! I like it, man!

This is surely clever, but probably shouldn't be used or marked as best practice. I'd have to performance test to be sure, but allocating an array on heap seems like it would be much slower than a branch with no array allocation. Maybe I'm wrong, in which case this would be a nice answer, but the bitwise and will always be better for both performance and readability.

If did that, than you should be proud of yourself. Constructing a algorithm to treat string dates ins't something trivial.

No let?

I know it's trivial, but how is mutating the original arrays being accepted as a valid solution?. Likewise for most of the other answers here

No const ?

Yeah, very disappointing to see this top-rated with such an obvious error.

so elegant!