js获取DropDownList的选中项的value值

后台数据绑定：

  string bdzsql =" *****";
        DataTable bdzData = SqlHelper.ExecuteDataTable(bdzsql);
        for (int i = 0; i < bdzData.Rows.Count; i++)
        {
            DDLbdz.Items.Add(new ListItem(bdzData.Rows[i]["bdz_name"].ToString(), bdzData.Rows[i]["bdz_code"].ToString()));
        }

前台展示：<asp:DropDownList ID="DDLbdz" runat="server">

 </asp:DropDownList>

js： var DDLbdz = document.getElementById("DDLbdz");            //获取DropDownList控件的引用  
           var departid = DDLbdz.options[DDLbdz.selectedIndex].value;   //获取选择项的值