How to add toAlternatingCase custom method to String class in JavaScript?

Question

I'm trying to add a custom method to the String class in JavaScript called toAlternatingCase, it will turn lowercase characters into uppercase and vice versa in the string that is called on, I'm trying to make it like the built-in toUpperCase/toLowerCase methods which don't take any arguments. this is a kata(challenge) on codewars.

Answer 1

This can be done by utilizing the prototype method to extend the String class. This probably isn't the most efficient way of doing this, but it can be achieved with something like this:

String.prototype.toAlternatingCase = function() {
  var ns = "";
  for(var i = 0; i < this.length; i++) ns += (this.slice(i, i+1) == this.slice(i, i+1).toUpperCase()) ? this.slice(i, i+1).toLowerCase() : this.slice(i, i+1).toUpperCase();
  return ns;
}

"String.prototype.toAlternatingCase".toAlternatingCase();
// Should return 'sTRING.PROTOTYPE.TOaLTERNATINGcASE'

This just loops through the string and reverses the case of each character, then returns that new result (without modifying the original string).