Solve 'altERnaTIng cAsE <=> ALTerNAtiNG CaSe'

[odv]

https://www.codewars.com/kata/alternating-case-%3C-equals-%3E-alternating-case/train/javascript

[RazvanBugoi]

String.prototype.toAlternatingCase = function () {
  let output = "";
  for (let i = 0; i < this.length; i += 1) {
    if ( this[i] == this[i].toLowerCase() ) {
      output += this[i].toUpperCase();
      } else {
      output += this[i].toLowerCase();
      }
    }
    return output;
}