代码如下：
<!DOCTYPE html>
<html>
<meta charset="UTF-8">
<title></title>
<head>
<script language="javascript">
function checklogin() {
if((myform.user.value != "")) {
if((myform.pwd.value != "")) {
return true
} else {
alert("密码不能为空");
return false
}
} else {
alert("用户名不能为空");
return false
}
}
</script>
<title></title>
</head>
<body>
<form action="form.html" name="myform" method="post" onSubmit="return checklogin()">
<input type="text" name="user" size="16"><br>
<input type="password" name="pwd" size="16"><input type="submit" value="登录" name="sub_1">
</form>
</body>
</html>