How to collect click on banner

[Boris ©avc]

I have a banner exchange commercial on my page. The code from banner
provider is in javascript. How can I change that code (the best would be in
php) to know who click on my banner?

If this would be normal html link i'd put hyperlink to mypage.php and then
use header('Location:'.$_GET['url']); on that page. But how to do it if
banner is supplied with Javascript code?

<div><center>
<script language="javascript"
src="http://www.bannerpage.com/script.php?id=1071"
type="text/javascript"></script><br>
</center></div>

Thanks for helping,
Boris