Caesars Cipher

function rot13(str) {
  // A-Z: 65-90
  let decoded = "";
  for (let i = 0; i < str.length; i++) {
    const code = str.charCodeAt(i);
    const shift = 0;
    if (code >= 65 && code <= 90) {
      shift = code + 13 > 90 ? -13 : 13;
    }
    decoded += String.fromCharCode(code + shift);
  }
  return decoded;
}

console.log(rot13("SERR CVMMN!"));