One of the simplest and most widely known ciphers is a Caesar cipher, also known as a shift cipher. In a shift cipher the meanings of the letters are shifted by some set amount. A common modern use is the ROT13 cipher, where the values of the letters are shifted by 13 places. Thus 'A' ↔ 'N', 'B' ↔ 'O' and so on. Write a function which takes a RO…

caesar-cipher.js

function createAlphabetArr(){
  const first = 'A'.charCodeAt(); 
  const second = 'Z'.charCodeAt();
  let alphabet = [];

  for(let code = first; code <= second; code++) {
    alphabet.push(String.fromCharCode(code))
  }
  return alphabet;
}

const alphabet = createAlphabetArr();

function rot13(str) { // LBH QVQ VG!
  const chars = str.split('');
  let ciphedText = [];

  let i = 0;
  while(i < chars.length){
    if(chars[i].match(/[A-Z]/i)){
      ciphedText.push(cipher(chars[i]));
    } else {
      ciphedText.push(chars[i])
    }
    i++;
  }

  return ciphedText.join('');
}

function cipher(letter){

 const currentPosition = alphabet.indexOf(letter);
 const shiftedPosition =  currentPosition < 13 ? currentPosition + 13 : (currentPosition + 13 - 25) - 1;

 return alphabet[shiftedPosition];
}

// Should return THE QUICK BROWN FOX JUMPS OVER THE LAZY DOG.
rot13("GUR DHVPX OEBJA SBK WHZCF BIRE GUR YNML QBT.");