Javascript String Prototype Create a ROT13 Cypher with a Custom Function

function rot13(string) { 
    return string.replace(/[a-z]/ig, function (character) { 
        let moveNumber = character.toLowerCase() < 'n' ? 13 : -13; 
        character = character.charCodeAt(0) + moveNumber; 
        return String.fromCharCode(character); 
    }); //  w  ww . ja  va 2  s . c  o  m
} 

console.log(rot13('hello')); 
console.log(rot13('HELLO')); 
console.log(rot13('uryyb')); 

function rot13(str) {
  var newStr = "";
  var intCode = NaN;
  for (var i = 0; i < str.length; i++) {
    if (str.charCodeAt(i) == " ") {
      // do nothing
    } else {// w w  w  .ja  v  a2  s .c om
      intCode = parseInt(str.charCodeAt(i));
      if (intCode < 65 || intCode > 90) {
        newStr = newStr + String.fromCharCode(intCode);
      } else {
        intCode += 13;
        if (intCode > 90) {
          intCode = (intCode - 90) + 64;
        }
        newStr = newStr + String.fromCharCode(intCode);
      }
    }
  }
  return newStr;
}

console.log(rot13("!"));
console.log(rot13("SERR PBQR PNZC"));
console.log(rot13("SERR CVMMN!"));
console.log(rot13("SERR YBIR?"));
console.log(rot13("GUR DHVPX OEBJA QBT WHZCRQ BIRE GUR YNML SBK."));