!DOCTYPE HTML>
html lang="en-US">
head>
    meta charset="utf-8">
    title>无刷新提交表单/title>
    style type="text/css">
        ul{ list-style-type:none;}
    /style>
/head>
body>
    iframe name="formsubmit" style="display:none;">
    /iframe>

    !-- 将form表单提交的窗口指向隐藏的ifrmae,并通过ifrmae提交数据。 -->
    form action="form.php" method="POST" name="formphp" target="formsubmit">
       ul>
            li>
                label for="uname">用户名：/label>
                input type="text" name="uname" id="uname" />
            /li>
            li>
                label for="pwd">密  码：/label>
                input type="password" name="pwd" id="pwd" />
            /li>
            li>
                input type="submit" value="登录" />
            /li>
       /ul>
    /form>
/body>
/html>

?php
  //非空验证
  if(empty($_POST['uname']) || empty($_POST['pwd']))
  {
    echo 'script type="text/javascript">alert("用户名或密码为空!");/script>';
    exit;
  }

  //验证密码
  if($_POST['uname'] != 'jack' || $_POST['pwd'] != '123456')
  {
    echo 'script type="text/javascript">alert("用户名或密码不正确!");/script>';
    exit;
  } else {
    echo 'script type="text/javascript">alert("登录成功!");/script>';
    exit;
  }