0x800a138f - JavaScript运行时错误：无法获取属性＆＃39;样式＆＃39;未定义或空引用

Question

我正在获取JavaScript

  

运行时错误：无法获得属性＆＃39;样式＆＃39;未定义或null   参考

运行以下代码时出现

错误 它的部分是lblSatisfyQuarterEndDate.style.display = "none";如果我删除那部分它运行正常。我想让文本框和标签消失然后值为False。

HTML

<div class="tdControl col-xl-6 nowrap">
     <asp:DropDownList ID="ddlSatisfyQuarterEnd_ID" runat="server" onchange="dd_changed()" ClientIDMode="Static" >
        <asp:ListItem  Selected="True" Value="-1">-- Select one --</asp:ListItem>
        <asp:ListItem Value="False">No</asp:ListItem>
        <asp:ListItem Value="True">Yes</asp:ListItem>
     </asp:DropDownList>

     <asp:RequiredFieldValidator ID="RequiredFieldValidator3" runat="server" ControlToValidate="ddlSatisfyQuarterEnd_ID" CssClass="ValidatorFailedImage" Display="Dynamic" ToolTip="Is Required" InitialValue ="-1" />
</div>
</div>
<div class="col-xl-4 col-lg-4">

<div class="tdLabel col-xl-6  nowrap">
   <asp:label ID="lblSatisfyQuarterEndDate" runat="server" Text=" Satisfy Quarter End Requirement Date:" />
</div>
<div class="tdControl col-xl-6  nowrap">
</div>

的JavaScript

var ddlSatisfyQuarterEnd_ID = document.getElementById("ddlSatisfyQuarterEnd_ID").value;
var ddlSatisfyQuarterEndDate = document.getElementById("ddlSatisfyQuarterEndDate");
var lblSatisfyQuarterEndDate = document.getElementById("lblSatisfyQuarterEndDate");


function dd_changed() {
    var ddlSatisfyQuarterEnd_ID = document.getElementById("ddlSatisfyQuarterEnd_ID").value;
    switch (ddlSatisfyQuarterEnd_ID) {
        case "True":
            ddlSatisfyQuarterEndDate.style.display = "inline";

            break;
        case "False":
            ddlSatisfyQuarterEndDate.style.display = "none";
            lblSatisfyQuarterEndDate.style.display = "none";
            break;
        default:
            ddlSatisfyQuarterEndDate.style.display = "none";

Answer 1

永远不要相信你在.aspx标记中看到的ID。查看浏览器中生成的HTML代码 您还可以改善服务器端的情境绑定ID。这是一个例子：

var ddlSatisfyQuarterEnd_ID = document.getElementById('<%#ddlSatisfyQuarterEnd_ID.ClientID%>').value;
var ddlSatisfyQuarterEndDate = document.getElementById('<%#ddlSatisfyQuarterEndDate.ClientID%>');
var lblSatisfyQuarterEndDate = document.getElementById('<%#lblSatisfyQuarterEndDate.ClientID%>');