[SOLVED]Caesars Cipher | What is wrong with my solution?

Tell us what’s happening:

My function does return correct output in the prompt, but for some reason FCC does not accep my code.

Your code so far

var A = "A".charCodeAt(0);
function rot13(str) { // LBH QVQ VG!
  var arr=[];
  for(i=0;i<str.length;i++) {
    var u = str.charCodeAt(i);
    if (!(A <= u && u < A+26)) {
    var v = (u-A+13)%26 + A;
  return arr.join("");

rot13("SERR PBQR PNZC");```
**Your browser information:**

Your Browser User Agent is: ```Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/60.0.3112.113 Safari/537.36```.

**Link to the challenge:**

Apparently, there was a bug in FCC. Now my identical code gets AC.