如何用javascript来验证数据的有效性？？
我写了一个简单的jsp实现了登录功能，可是有一个地方我一直没有搞清楚，我本来写了一段javascript来检查看用户是否在用户名和密码框中输入了数据，如果没有就发出一个提示。可是我自己试了，我在用户名和密码框中甚么也不填就直接按提交按钮，结果就报错了。高手帮帮我，看看这个是甚么原因。jsp代码如下（很简单）：
<%@page language= "java " contentType= "text/html;charset=gb2312 "%>
<html>
<head>
<meta http-equiv= "Content-Type " content= "text/html;charset=gb2312 ">
<meta http-equiv= "Content-Language " content= "zh-cn ">
<title> 登录 </title>
<!-- javascript函数validateLogin(),用来验证是否填写了用户名和密码：-->
<script language= "JavaScript "> <!--
function validateLogin(){
var strUsername = window.document.formLoign.username.value;
var strPassword = window.document.formLoign.password.value;
if(strUsername == " "){
alert( "请输入用户名！ ");
return false;
}
if(strPassword == " "){
alert( "请输入密码！ ");
return false;
}
}
-->
</script>
</head>
<body>
<!-- 提交时调用JavaScript函数validateLogin()来验证是否填写了用户名和密码：-->
<form method= "post " name= "formLogin " action= "verifylogin.jsp " onSubmit= "javascript:return validateLogin(); ">
<table align= "center " bgcolor= "#cccccc " border= "0 " cellPadding= "0 " cellSpacing= "0 " width= "275 ">
<tr>
<td align= "right " height= "48 " vAlign= "bottom " width= "94 "> 用户名： </td>
<td height= "48 " vAlign= "bottom " width= "172 "> <input name= "username " maxLength= "20 " size= "16 "> </td>
</tr>
<tr>
<td align= "right " height= "48 " width= "94 "> 密码： </td>
<td height= "48 " width= "172 "> <input name= "password " type= "password " size= "16 " maxLength= "20 "> </td>
</tr>
<tr>
<td align= "right " height= "48 " width= "94 "> </td>
<td height= "48 " width= "172 ">
<input name= "Submit " type= "submit " value= "提交 ">
<input name= "Reset " type= "reset " value= "重置 ">
</td>
</tr>
</table>
</form>
</body>
</html>
要怎么样做才能验证用户不填任何数据的情况？？
[解决办法]
没你那么写过，我这样写的
<script language= "javascript ">
function Juge(form_insert)
{
if(form_insert.cLoginName.value == " ")
{
alert( "用户名不能输入空值 ");
form_insert.cLoginName.focus();
return (false);
}
if(form_insert.cLoginPwd.value == " ")
{
alert( "密码不能输入空值 ");
form_insert.cLoginPwd.focus();
return (false);
}
}
</script>
[解决办法]
这样就可以了：
<script language= "JavaScript "> <!--
function validateLogin(form){
var strUsername = form.username.value;
var strPassword = form.password.value;
if(strUsername == " "){
alert( "请输入用户名！ ");
return false;
}
if(strPassword == " "){
alert( "请输入密码！ ");
return false;
}
}
-->
</script>
<form method= "post " name= "formLogin " action= "verifylogin.jsp " onSubmit= "javascript:return validateLogin(this); ">
