[Solved]Why str.charAt(-1) doesn't work?

Question

It's a challenge code Named "Gapful Numbers". My code only works for 3 numbers. Why the negative index doesn't work?
https://code.sololearn.com/W91RQKB05NE3/?ref=app

Answer 1

You are trying to access the character at index -1, and that doesn't really exist. You can either use numStr.slice(-1), or numStr.charAt(numStr.length - 1)

Answer 2

Ok, Ok Thank u so much❤

Answer 3

no