JS简单操作select和dropdownlist

   <select id="selectID" onchange="return showMessage()">             <option value="0">==请选择==</option>             <option value="1">是</option>             <option value="2">否</option>   </select>  <script type="text/javascript" language="javascript">          function showMessage() {              if (document.getElementById("selectID").options[document.getElementById("selectID").selectedIndex].value == 1) {                  alert("你好，你选择了第 1 个");                  document.getElementById("txtContractName").setAttribute("enable",false);              }              else if (document.getElementById("selectID").options[document.getElementById("selectID").selectedIndex].value == 2) {                  alert("你好，你选择了第 2 个");              }          }    </script>//js操作服务器控件dropdownlist    <asp:DropDownList ID="ddlFolder" runat="server" SkinID="ddlSkin" AutoPostBack="false" OnSelectedIndexChanged="ddlFolder_SelectedIndexChanged">            <asp:ListItem Value="0">选项0</asp:ListItem>     <asp:ListItem Value="1">选项1</asp:ListItem>      </asp:DropDownList>        <asp:DropDownList ID="ddlFolder" runat="server" SkinID="ddlSkin" AutoPostBack="false" OnSelectedIndexChanged="ddlFolder_SelectedIndexChanged">  <asp:ListItem Value="0">选项0</asp:ListItem> <asp:ListItem Value="1">选项1</asp:ListItem>     </asp:DropDownList> JS代码：document.getElementById("ddlFolder").value="0";//0为你要选中的项的value  2.根据Text值设置选中某项var DropDownListCurrencyNew     =  document.getElementById("ddlFolder");for(i = 0; i < DropDownListCurrencyNew.options.length; i++)   {          if(DropDownListCurrencyNew.options[i].text == "选项0")               {               DropDownListCurrencyNew.options[i].selected = true;           }   }二：js读取DropDownList选中项的value和textValue：var selValue = document.getElementById("DropDownList1").options[document.getElementById("DropDownList1").selectedIndex].value;Text：var selText = document.getElementById("DropDownList1").options[document.getElementById("DropDownList1").selectedIndex].text;