Javascript - Does The ListBox SelectedIndexChanged Event Require Postback

I'm trying to add a JavaScript function to show all selected items from a ListBox as concatentated strings in a Label on the page. It's needed because AutoPostBack="true" will cause the ListBox to scroll all the way back to the first selected item.

So this code works:

<script type="text/javascript">
function Updatelist() {
var sel = document.getElementById('<%=lstbxStuff.ClientID%>');
var lbl = document.getElementById('ctl00_cph_lblSelectedStuff');

[Code]....

Unfortunately I still need the code behind SelectedIndexChanged delegate. Is there a way to use both of these without doing a PostBack? When I set AutoPostBack="false", my delegate never seems to be reached.