Ajax Updater should work on js function call... But it dont...

[eluser]Rubiz'[/eluser]
Hi!! I'm trying to do a Ajax Updater function outside button click; I had to do this in a normal javascript function, I'm trying like that:

Code:

<!--
    function setAdress()
    {
        var adress = '<?=base_url()?>index.php/email/preview/' + $('id_category').getValue();
        new Ajax.Updater('preview', adress ,{evalScripts:true});
    }
-->

It should work, don't?
Its not working... anyone knows why?