alternatingCase.js

// Description:
// altERnaTIng cAsE <=> ALTerNAtiNG CaSe
// 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"

//mine
String.prototype.toAlternatingCase = function () {
  let newString = "";
  for (let i = 0; i < this.length; i++) {
    if (this[i] === this[i].toUpperCase()) {
      newString = newString + this[i].toLowerCase();
      continue;
    }
    if (this[i] === this[i].toLowerCase()) {
      newString = newString + this[i].toUpperCase();
      continue;
    }
    newString = newString + this[i];
  }
  return newString;
};

//better and shorter
String.prototype.toAlternatingCase = function () {
  return this.split("")
    .map((a) => (a === a.toUpperCase() ? a.toLowerCase() : a.toUpperCase()))
    .join("");
};