源代码：
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312">
<meta name="Author" content="刘江波">
<script type="text/javascript">
function login(){
var userName=document.getElementById("userName").value;
var pwd=document.getElementById("pwd").value;
var repwd=document.getElementById("repwd").value;
var address=document.getElementById("address").value;
var matchResult=true;
if(userName==""||pwd==""||repwd==""||address==""){
alert("请确认是否有空缺项！");
matchResult=false;
}else if(userName.length<6||userName.length>20){
alert("用户名长度应在6到20个字符之间！");
matchResult=false;
}else if(userName==pwd||userName==repwd){
alert("密码或重复密码不能和用户名相同！");
matchResult=false;
}else if(pwd.length<6||pwd.length>20||repwd.length<6||repwd.length>20){
alert("密码或重复密码长度应在6到20个字符之间！");
matchResult=false;
}else if(pwd!=repwd){
alert("密码和重复密码不同，请重新输入！");
matchResult=false;
}else if(userName.length<6||userName.length>20){
alert("用户名长度应在6到20个字符之间！");
matchResult=false;
}
if(matchResult==true){
var mailreg = /^w+@w+(.w+)+$/;
if(!address.match(mailreg)){
alert("邮箱格式不正确");
matchResult=false;
}
}
if(matchResult==true){
if(userName.charAt(0)>=0&&userName.charAt(0)<=9){
alert("用户名不能以数字字符开始！");
matchResult=false;
}
}
return matchResult;
}
</script>
<title>用户注册及验证</title>
</head>
<body>
<center>
<form name="loginForm" action="http://www.ytu.edu.cn" onsubmit="return login()" method="post">
<table bgcolor="#6666FF" width="300" cellspacing="0" cellpadding="0" border="0" align="left" valign="top">
<tr>
<td class="table-title" colspan="2" align="center" bgcolor="#3366FF">用户注册</td>
</tr>
<tr>
<td width="130" height="28" align="left">登录用户名</td>
<td><input id="userName" name="userName" type="text" class="input"></td>
</tr>
<tr>
<td width="80" height="28" align="left">登录密码</td>
<td><input id="pwd" name="pwd" type="password" class="input"></td>
</tr>
<tr>
<td width="80" height="28" align="left">重复输入密码</td>
<td><input id="repwd" name="repwd" type="password" class="input"></td>
</tr>
<tr>
<td width="80" height="28" align="left">有效邮箱地址</td>
<td><input id="address" name="address" type="text" class="input"></td>
</tr>
<tr>
<!--<td width="10" height="28" align="left"></td>-->
<td colspan="2">
<input type="submit" value="登录">
<input type="button" value="取消" onClick="reset()"></td>
</tr>
</table>
</form>
</center>
</body>
</html>
效果实现：