This solution was authored 2013-10-12 btw. Latest Node.js version was v0.11.7

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.

I don't get it, if generally is ok, but in one of the languages the convention is different, why the kata should be renamed affecting all languages? I'd have probably used PascalCase from the beginning, but changing the name of the kata and the function's name in every language isn't free. You need to make all tests backward compatible to not render all solutions invalid.

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