How does this replaceAt function work?

Question

Could you please explain how this piece of code works?

String.prototype.replaceAt = function(index, character) {
    return this.substr(0, index) + characte         


        

Answer 1

Lets imagine this easy case:

"0123456789". replaceAt(2/*index*/,"000"/*character*/)

Then this happens:

this.substr(0, index/*2*/)//"01"
 + character //"000"
 + this.substr(index/*2*/+character.length/*3*/)//"56789"

Output:

0100056789