function rot13(str) {
    var nstr="";
    for(var i=0; i<str.length; i++){
        //Checks if character lies between A-Z
        if(str.charCodeAt(i) < 65 || str.charCodeAt(i) > 90) {
            nstr += String.fromCharCode(str.charCodeAt(i));
            continue;
        }
        //N = ASCII 78, if the character code is less than 78, shift forward 13 places
        if(str.charCodeAt(i) < 78){
            nstr += String.fromCharCode(str.charCodeAt(i) + 13);
        }
        else{
            //Otherwise shift the character 13 places backward
            nstr += String.fromCharCode(str.charCodeAt(i) - 13);

        }
    }

    return nstr;
}

//Solution with Regular expression and Array of ASCII character codes
function rot13(str) {
  //retCharArray is an Array of character codes for the solution
  var rotCharArray = [];
  //regular expression for all upper case letter from A to Z
  var regEx = /[A-Z]/ ;
  //split str into a character array
  str = str.split("");
  //iterate over each character in the array
  for (var x in str) {
    //regEx.test(str[x]) will return (true or false) if it maches the regEx or not
    if (regEx.test(str[x])) {
    //checks if the new character code is greater or equal to 65 (letter A)
      if (str[x].charCodeAt()-13 >= 65) {
        rotCharArray.push(str[x].charCodeAt()-13);
      } else {
        rotCharArray.push(str[x].charCodeAt()+13);
      }
    } else {
      rotCharArray.push(str[x].charCodeAt());
    }
  }
  //make a string with character codes from an array of character codes
  str = String.fromCharCode.apply(String, rotCharArray);
  return str;
}


// Change the inputs below to test
rot13("LBH QVQ VG!");

function rot13(str) {
  // Split str into a character array
  return str.split('')
  // Iterate over each character in the array
    .map.call(str, function(char) {
      // Convert char to a character code
      x = char.charCodeAt(0);
      // Checks if character lies between A-Z
      if (x < 65 || x > 90) {
        return String.fromCharCode(x);  // Return un-converted character
      }
      //N = ASCII 78, if the character code is less than 78, shift forward 13 places
      else if (x < 78) {
        return String.fromCharCode(x + 13);
      }
      // Otherwise shift the character 13 places backward
      return String.fromCharCode(x - 13);
    }).join('');  // Rejoin the array into a string
}