Get query string in js file?

Question

JavaScript

<script type="application/javascript" src="checkout.js?a=5 "></script>

If we are talking about a php file by going to /checkout.php?a=5 in the checkout.php file we can ask $_SERVER['QUERY_STRING'] and get that QUERY_STRING.
If we load the script as above, allegedly passing QUERY_STRING into it, then all we can do is parse the entire code of the document and find this script tag in it and see what query string it has.
As far as I understand, we do not recognize the query string through location. right ?
Or are there methods other than source code parsing?

Answer 1

I came up with the solution myself. Upload the script to the php. For example so

<?
$sf=$_SERVER['QUERY_STRING'];
header("Content-Type: application/javascript; charset=utf-8");
?>
var test="<?=$sf?>";
alert(test);

include this file in the header
Output // a=5