alternating case.js

// 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 = function () {
    return this.split('').map(el=> {
      if (el.toUpperCase() == el) return el.toLowerCase()
      else return el.toUpperCase()
    }).join('')
  }