Passing variable from JS to PHP within the same page

Question

I know that PHP is a server-side script while JS is the client-side thus when the page loads, it will load PHP before JS thus it is impossible to do so. What I want is an alternative method to perform my JS task which is to take the value after the ? in the address bar (//localhost/Task/delete.php?ID=1). 

<script language="javascript" type="text/javascript" >
var url = window.location.href;
var params = url.split('?ID=');
var fdf = (params[1])
alert(fdf);

</script>

<?php
$random = $_GET["fdf"];

echo $random;
?>

Can someone please help me?