Necessary to add up this querystring for ascx?

Hello,
There is a way that you can get the latest javascript by appending the querystring like datestring..
http://blahblah/your.js?_t=58738734 something like this so that the brower get the always latest js file...
BTW, let's say
in OnInit, a ascx file is loaded dynamically.
protected override void OnInit(...) {
 Control c = this.LoadControl("MyUserControl.ascx");
..}
In MyUserControl.ascx..javacript is used in that markup file like..
<script language="javascript" type="text/javascript">        $(function() {
               blahblah..js initi..something my business logic..
       });
..
</script>
works fine..but..when I change the javascr ...