javascript event on controller ?

[eluser]Fribos[/eluser]
Hi, i'm trying to include a javascript alert on a controller function but it seems like doesnt work. I'm just started with AJAX and JS codding.

Here is pertinent function from my view

Code:

function checkBan(){
    $.ajax({
       type: "POST",
       url: "xxxxxxxxxxxxxxxxxxxxx/fmchat/check_ban",
    });
};

setInterval (checkBan, 1500);

This is my controller function

Code:

function check_ban() {
      if ($this->session->userdata('ban')<>'') {
        ?&gt;
        <.script language="JavaScript" type="text/javascript">
           .alert('User banned');  
        </.script>
        &lt;?
      }
    }

I dont know if it's an ajax problem or just javascript is not allowed on controllers.
I'll regards every kind of tip, help or comment.
Thanks