alternatingCase.js

/* 

Define String.prototype.toAlternatingCase (or a similar function/method such as to_alternating_case/toAlternatingCase/ToAlternatingCase in your selected language; see the initial solution for details) such that each lowercase letter becomes uppercase and each uppercase letter becomes lowercase. For example:

"hello world".toAlternatingCase() === "HELLO WORLD"
"HELLO WORLD".toAlternatingCase() === "hello world"
"hello WORLD".toAlternatingCase() === "HELLO world"
"HeLLo WoRLD".toAlternatingCase() === "hEllO wOrld"
"12345".toAlternatingCase()       === "12345"                   // Non-alphabetical characters are unaffected
"1a2b3c4d5e".toAlternatingCase()  === "1A2B3C4D5E"
"String.prototype.toAlternatingCase".toAlternatingCase() === "sTRING.PROTOTYPE.TOaLTERNATINGcASE"
As usual, your function/method should be pure, i.e. it should not mutate the original string.



*/

String.prototype.toAlternatingCase = function () {
  let result = '';
  for (let i = 0; i < this.length; i++) {
    if (this[i].charCodeAt() >= 65 && this[i].charCodeAt() <= 90) {
      result += this[i].toLowerCase();
    } else {
      result += this[i].toUpperCase();
    }
  }
  return result;
};