Onclick does nothing

Been googling jquery posting, xhr calls, ajax. Tried:

[download_page.php]
class download_page extends MY_Controller {
function add_row() {
alert("downloading");
}
}

[downloads.php]
<a href="http://www.downloaddocs/file.doc" onclick="<?=site_url('download_page/add_row')?>">

.. but the add_row function still not being called. If I put a syntax error in add_row() then the downloads.php page gives an error.

The developer who made the site that I'm trying to add the click records to no longer around, which is the problem as would've taken him 2 mins.