JS小白求解为什么lable标签的值页面上没改变

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="_Default" %><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title></title>
    <script src="js/jquery-1.4.1.min.js" type="text/javascript"></script>
    <script type="text/javascript" language="javascript">
        function Regs() {
            var uName = document.getElementById("txtUserName").value;
            var uPwd = document.getElementById("txtPwd").value;
            var NameMeg = document.getElementById("LbNameMeg");
            var PwdMeg = document.getElementById("LPwdMeg");
            if (uName != "" && uPwd != "") {
                document.getElementById("LbNameMeg").display = "none";
                document.getElementById("LPwdMeg").display = "none";
            }
            else {
                if (uName == "") {
                    NameMeg.value = "*用户名不能为空！";
                    NameMeg.style.display = "block";
                } 
                 if (uPwd == "") {                    PwdMeg.value = "*密码不能为空！";
                    PwdMeg.style.display = "block";
                }
            }
        }
    </script>
</head>
<body>
    <form id="form1" runat="server">
    <div>
        <table>
            <tr>
                <td colspan="3">
                    <h2>
                        用户注册</h2>
                </td>
            </tr>
            <tr>
                <td>
                    用户名称：
                </td>
                <td>
                    <asp:TextBox ID="txtUserName" runat="server"></asp:TextBox>
                </td>
                <td>
                    <asp:Label runat="server" ID="LbNameMeg" Text="222"></asp:Label>
                </td>
            </tr>
            <tr>
                <td>
                    用户密码：
                </td>
                <td>
                    <asp:TextBox ID="txtPwd" runat="server"></asp:TextBox>
                </td>
                <td>
                    <asp:Label runat="server" ID="LPwdMeg" Text="1111"></asp:Label>
                </td>
            </tr>
            <tr>
                <td colspan="3">
                 <input type="button" value="注  册"  id="btnReg" name="注册" onclick="Regs()"/>
                </td>
            </tr>
        </table>
    </div>
    </form>
</body>
</html>

解决方案 »

  1.   

    var uName = document.getElementById("<%=txtUserName.ClientID%>").value;
    var uPwd = document.getElementById("<%=txtPwd.ClientID%>").value;
    var NameMeg = document.getElementById("<%=LbNameMeg.ClientID%>").value;
    var PwdMeg = document.getElementById("<%=LPwdMeg.ClientID%>").value;
      

  2.   

    value属性是只针对表单元素的，Label实际上会在页面中生成Span标签，是没有value属性的。
                    if (uName == "") {
                        NameMeg.innerHTML= "*用户名不能为空！";
                        NameMeg.style.display = "block";
                    } 
                     if (uPwd == "") {                    PwdMeg.innerHTML = "*密码不能为空！";
                        PwdMeg.style.display = "block";
                    }
      

  3.   

    因为你label里面加了runat="server" ，ID会发生变化。不信你自己查看一下编译后的页面源代码
      

  4.   


    有jquery直接用jquery的更方便
    $("#LbNameMeg").html("xxxxx")
      

  5.   

    对Label来说在后台代码里是用Text,在js中是innerHTML