I'll say, but keep in mind that this approach is more concise and efficient than your method, especially for larger numbers.

he doesn't use template literals.

Wow... that's insane

You are right. I know you are not supposed to 'invent the wheel again' but this exercise is great to learn algorithmic thinking and complex concepts like recursion.

I think it's better to use this space to do what you wanted to do at first. This is a great exercise to understand and practice algorithms and recursion

it removes the character that was there previously i think

yeah that's the way she goes sometimes. i do these challenges just to nail into my brain the kinds of built in functions you can use, because I hate doing what you did and realizing I spent so much time for no reason. A good rule of thumb is that for 7/8 kyu problems, you generally don't have to reinvent any wheels.

Your codes are very clean

nice

checks for negative numbers

I think it would have been better if you had tried to get to the algorithm properly. You would have learned more. Using the solution is good when you already know how to get to the solution.

A little disappointing to see that there is already a solution to the problem. Surely that function uses the same algorithms that we are supposed to write. But using this solution takes away all the fun from the problem. It's literally like writing a "hello world." The only value of the kata itself is having discovered that this function exists, I guess.

Humm? Is not your own solution read through the string a lot mor of times? doing a cicle for you are reading the string mor than once for each character.

Why set such conditions in the first place?
Kata is only for experience, in reality you get slapped on hand for doing like this solution.
How I can blocked exersise from this 'coder'?