You can process those GET parameters on the server where the **.js is hosted, so that it will dynamically change the js file. And your server somehow processes the file, replacing that **.js template file dependent on what request was sent.
Set the global variables on the page where ***.js is loaded, like this. This will then be available in the JS script.
In the HTML document … somewhere.
window.YourVariableName = 'Value';
Access it in the script …
var handle = window.YourVariableName || null;