Selecting item from ASP.NET listbox using jquery

 $("#btnSave").click(function() {

 var varClassID="";
                $('#ddlChildClass :selected').each(function(i, selected){
               if(varClassID=="")
                    varClassID=$(selected).val();
               else
                    varClassID=varClassID+","+$(selected).val();
                 });

}

====================================


<asp:ListBox ID="ddlChildClass" runat="server" SelectionMode="Multiple">
                    </asp:ListBox>


<input id="btnSave" type="button" value="Save" class="buttonId" runat="server" />