You're not even enforcing the use of splice.

Check this solution out, as well as my own solution.

This kata is terrible by design. There's no point in using a method modifying the array AND returning the same array as the result of the operation (on success the result is an array, but on failure it's boolean - great idea). Because of this senseless decision filter is also forbidden as "it allows you to solve the task in a way that was not intended" (this is not even mentioned in the description).

Please add random tests.

Whenever I see katas like this, I always wonder what the codewars policy say about editing katas that is not yours!

1. Can I just dive in and change (or improve) the concept? (Of course this will almost all the time lead to all previous solutions becoming invalid).
2. When you look at the Issues reported, you see some dating back to several years (3 years in the case of this particular kata) does it mean these katas should just be left alone?

I am sorry, but this Kata does not force you to use any language related features ..... IMO, it should be changed.

Need more tests.
One more.