ROT13 - Caeser's Cipher

rot13.js

function rot13(string) {
  var set = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ';
  var translation = '';
  var string_length = string.length;
  var position;
  
  for (var index = 0; index < string_length; index++) {         
    position = set.indexOf(string[index]);

    if (position >= 0) {
      translation += set[(position + 13) % 26];
    } else {
      translation += string[index];
    }
  }

  return translation;
}