The main problem here is that Codewars does not indicate which JavaScript version the katas and solutions target.

There is also no indication how old this kata and the solutions are, in fact they are from a time when fat arrows and other modern constructs were not yet available in JavaScript.

Another problem is that there is no indication whether the solution should be optimized for speed or for readability.

If the lists are very small and the function is not used frequently, a simple and readable solution might be preferred over an optimized and faster one.

Looks like you start to recognize the whole vanity of life...

Would still consider this a pretty obvious and readable Python solution, not a "clever hack" and not in any way terrible.

Even JavaScript and other languages used in Code Wars have evolved and now have features that were not available 5 years ago.

Also note that this is all work by volunteers. If anybody wants to create a new kata with a better description or tests, please go ahead. Or try to convince the author with positive criticism and friendly feedback. Personally I don't feel motivated to go back to what I posted years ago and put time and efford in changing it or adapting it to new standards, if all I get are snarky comments that "the description is a mess" and what is missing as feedback.

Also keep in mind that in a real developer's life problem descriptions are much less complete and exact, often misleading, often formulated by people coming from different domains who think very differently from you. I don't think katas should treat people with velvet gloves and make the path too smooth and straight forward, but give people something to think and experiment, that they can apply in real life as well.

Keep cool and don't make a drama out of everything. There will be always katas that you don't get or don't like but are fun and helpful for others. I like the diversity and have no problem with some mixed quality.

See my comment when somebody complained it's O(n^2). Btw, O(2n) = O(n).

What is readable is also a matter of experience and taste. For instance, some believe writing "u" instead of "you" is better readable, others don't think so.