Caesars Cipher, how to pass on special characters?

Tell us what’s happening:

can someone help me figure out how to pass on the special symbols.
everything works fine except the special characters.

Your code so far

function rot13(str) { // LBH QVQ VG!
  var arr=[];
  for(var i=0;i<str.length;i++){
   arr[i]= str.charCodeAt(i)+13; 
    arr[i]=arr[i]%91 +65;
return str;

// Change the inputs below to test
rot13("SERR CVMMN!");

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Link to the challenge:

In your for loop you have

    arr[i] = str.charCodeAt(i) + 13;

This line converts any character (letters or symbols) to ASCII code. You should only convert the characters which are the letters A-Z.