前台
<asp:DropDownList runat="server" CssClass="form-control" ID="Dbo_xnxq"></asp:DropDownList>
<script type="text/javascript">
var xnxq = document.getElementById("Dbo_xnxq");
var dtext = xnxq.options[xnxq.selectedIndex].text;
alert(dtext);
</script>