I only try to explain the swap mechanism because it took time for me to understand, so I made the post because newbies could understand. Sorry I am a teacher.
But you are right, no checking of the parameters is always a bad thing.

The variable names tell you the truth. lol

I think this kata is difficult for a 8 kyu at least in C.

What do u think about?

Thanks, for the answer, I understand know how it works.

The problem is that I can't see the '\u200D' chars in the string. But if I test the length of the string '‍on‍yirmi‍otuz‍kırk‍elli‍altmış‍yetmiş‍seksen‍doksan' the chars are there. I don't know if it's a matter of the browser or the system or it's typed in a way that the chars are hidden. In any case is a clever solution, but in my point of view not didactic at all.

Someone more clever than I could ilustrate how the split function works in these strings?
I don't see the way it can convert that in an array of the number words. Where are the separators? hidden? What am I mising?
I tested the code and it works. I tested alone the split part and it works, but I can't figure out how.

Thanks for the answers.

I'm going to give up this one for a while, until I get better skills.