I made the JS-version of this kata, so the chicken and egg was made simultaneously :)

This is a carbon copy of the actual test assertion. What came first who knows?...Chicken and egg...

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_expressions

clean, but the intital split/filter repetition seems a bit high in performance cost and very reduceable.

insane

20 lines? 🙂

very nooice

Pretty clean, love it

Or you could just use a.localeCompare(b) instead of trying to find the index. Misread that.

I'd say the best say is

[...'abcdefghijklmnopqrstuvwxyz']

How this test works? can you explain this?

To conclude: the best possible solution for this problem is a O(n) complexity (check my solution),
which is scaled out to O(2n) with this most "Clever"/"Best Practice".

The point is how s/he leverages pass by reference in his/her solution.

Thanks for your informative comment.