Very clever

Although I initially like my version better, I like the exiplitness and clarity of this version.

I didn't know I can use .reverse. It seems to work out well.

I liked this one, but I think for some can be a bit hard to understand.

гениально

The argument isn't being assigned to a function. The function name required by the kata (stringToNumber) is being assigned to an existing function. This is similar:
var rand = Math.random

now you have a function, rand, that can do the same thing Math.random can.

божественно

Practice makes perfect.

That's a good point, but code tracing is something that every wannabe developer should be aware of. If you will need the original arg in any other place in your code, you can't mutate it and if not, that's not a thing. This is something that should be learned at a very early stage of coding.

As codes are abstractions, you ALWAYS should be AWARE of the CONTEXT where it is inserted.

Woah that's cool. I didn't know argument could be asigned to a function and the function would be performed on it.

or extract "pure" factorial method, which can be made recursive

Keep grinding, mate! Sky is the limit.

Hah, my first kata which I done. And yes, it was easy. But I think Im too stupid for coding(. Its just begining...