caesarCipher.js

function caesarCipher(str, num) {
    num = num % 26;
    let lowerCaseString = str.toLowerCase();
    let alphabet = 'abcdefghijklmnopqrstuvwxyz'.split('');
    let newString = '';
  
    for (let i = 0; i < lowerCaseString.length; i++) {
      let currentLetter = lowerCaseString[i];
      if (currentLetter === ' ') {
        newString += currentLetter;
        continue;
      }
      let currentIndex = alphabet.indexOf(currentLetter);
      let newIndex = currentIndex + num;
      if (newIndex > 25) newIndex = newIndex - 26;
      if (newIndex < 0) newIndex = 26 + newIndex;
      if (str[i] === str[i].toUpperCase()) {
        newString += alphabet[newIndex].toUpperCase();
      }
      else newString += alphabet[newIndex];
    }
  
    return newString;
  }
  
  caesarCipher('Zoo Keeper', 2); // Bqq Mggrgt
  
  caesarCipher('Javascript', -900); // Bqq Mggrgt
  
  caesarCipher('Dhimas Akbar', 27); // Eijnbt Blcbs