Agreed. Mine is fugly in comparaison... ;-)

Well, some of the upvoted solutions do not cover all the bases, or fail on some cases. I like to test them sometimes when they look kinda iffy.

Thanks for this Kata. My suggestion would be to clearly state the type and form of the output. I started assuming it was a string.... Silly me!

Agreed. The new RegExp should go like this:

new RegExp( "[" + s[i] + "]", "gi")

Great use of spread syntax!

Could you please explain?

Liked it, though ranked somewhat high IMHO.
Thanks g964 for this one!

You're right, just wanted to mention the recycling of the parameter.

Not working

Mutating the input values and rather WET, not great....

Nice & clean! Love it.

Agreed. It seems to me this and most of other solutions are very resource intensive.
A simple for loop would be much more economical.

This is brute force. RegExp or other are way more efficient.
Also, it modifies the input. Not good practice.

I really like this solution, clean and simple. Kudos!