Roman 13 challenge help

JavaScript
1 
function rot13(str) {
  // LBH QVQ VG!
  return str.replace(/[A-Z]/g, L =>
    String.fromCharCode((L.charCodeAt(0) % 26) + 65)
  );
}

This is from the Roman 13 code challenge.
Can anyone explain to me  why charCodeAt(0) in this case ?

Thanks for your help.
2

Because L is a string. It is a string of 1 character and you are getting the code of the first (and only in this case) character. Some languages have a separate data type for characters, but JS does not. In JS, the closest we have to a character is a string that is only one character long.

3

You do not need to pass anything to charCodeAt if you always just want the first character in the string (or if it is a single character string).

And maybe just a little clarification, L is a variable (argument), it contains the match.

function rot13(str) {
  return str.replace(/[A-Z]/g, match => {
    console.log(match); // L, B, H, Q, V, Q, V, G
    return String.fromCharCode((match.charCodeAt() % 26) + 65)
  });
}

console.log(rot13('LBH QVQ VG!'));
// YOU DID IT!
4

Thanks guys for the help