Caeser Cipher rough

cipher.js

function rot13(str) { // LBH QVQ VG!
  var result = [],
      rotdex = str.split(''),
      charcode;

  for (i = 0; i < rotdex.length; i++) {
    charcode = (rotdex[i].charCodeAt() - 13);
    if ((charcode + 13) == 32 || (charcode + 13) == 33 || (charcode + 13) == 46 || (charcode + 13) == 63) {
      result.push(String.fromCharCode(charcode + 13));
    }
    else if ((charcode >= 65) && (charcode <= 90)) {
      result.push(String.fromCharCode(charcode));
    } 
    else {
      result.push(String.fromCharCode(charcode + 26));
    } 
  }
  console.log(result);
  
  return result;
}