I wanted to POST variable from JS file to PHP using AJAX. I have both these files in same folder but when I run php code, I don´t see: Warning: Undefined array key "profile_viewer_uid" in C:\xampp\htdocs\zkoska\ppp.php on line 2

Why would be profile_viewer_uid undefined if I have it in JS and code also contains connection: url: "PPP.php", What is wrong here?
Thank you

javas.js

<script>
var profile_viewer_uid = 1;
$.ajax({
  url: "PPP.php",
  method: "POST",
  data: { "profile_viewer_uid": profile_viewer_uid }
}) 
</script>

ppp.php

<?php
 $profile_viewer_uid = $_POST['profile_viewer_uid'];
 echo($profile_viewer_uid);
 // prints 1
 ?>