Call a server function from javascript

How can I force a postback and call a codebehind funktion from javascript?
I want to do something like this:

aspx-file

Code:

---

<script type="text/javascript">
function OnRowSelecting(sender, args) 
{
    ServerFunc();
}
</script>

---

Codebehind c# file

Code:

---

private void ServerFunc()
{
    //…
}

---

http://ajax.schwarz-interactive.de/d...ajaxsample.zip

download the zip. In the zip there's a Word document with tutorial