Rot13 decoder

rot13decoder.js

function rot13(S) {
  //create our alphabet
  let az = 'abcdefghijklmnopqrstuvwxyz'.toUpperCase().split('');
  //create an array for the string passed in
  let splitS = S.split(' ');
  //recreate the new arrays
  let newString = splitS.map((word) => {
    let splitWord = word.split('');
    let newWord = splitWord.map((letter) => {
      // when letter = az
      let letterIndex = az.indexOf(letter);
      if (letterIndex > 13) {
        return az[letterIndex + 13 - 26];
      } else return az[letterIndex + 13];
    }).join('');
    return newWord;
  }).join(' ');
  return newString;
};

console.log(rot13('LBH QVQ VG')); // YOU DID IT
console.log(rot13('WOO FOR MATH')); // JBB SBE ZNGU