Can someone explain?

Thats cheating man xd

• declare your variables
• do not modify your inputs
• the IIFE would be better expressed as a recursive function returning a ( the ) result
• factor out things like sum
• express your intent more clearly in your code
• using splice may seem attractive, but it's generally slow; try avoiding it

It's not as performant as it could be, but it has more or less the right asymptotic performance. It's not as maintainable as it could be ( and this is bigger than you possibly think ), but .. it works.

I also thought that would be cool to solve this using regex!

In my case I used join('') enstead of join('-') and solved the /222/ problem by checking how many numbers are behind like this /^(...)*2{3}

You can see full code here:
https://www.codewars.com/kata/reviews/525caa5c1bf619d28c000338/groups/61e41f559a04f80001a6b80a

Can you review my JavaScript solution?

https://www.codewars.com/kata/reviews/58e781d2c731c115d9000e01/groups/61e2e39054e22a00012dde53