关于用iframe实现无刷新表单提交

HTML：代码

<iframe name="FORMSUBMIT" width="1" height="1" ></iframe>
<form action="login.php" method="post"  target="FORMSUBMIT" name="form1">
<div class="TxtUser" id="userlogindiv">
username:<input name="username" id="username" type="text"   size="18" ><br/>
password:<input name="passwords" id="passwords"  type="password"  size="18" ><br/>
<input type="submit" name="Submit" value="login" />
</div>
<span id="login_ad"></span>
</form>

PHP：代码

<?
$accounts=$_POST['username'];
$passwords=$_POST['passwords'];
$showdata="登录成功";
if($accounts=="liujianxun" && $passwords=="123456")
{
    echo" "</span><span style="color:#0000CC;">;</span><br></li><li>&nbsp;&nbsp;&nbsp;&nbsp;<span style="color:#FF0000;">echo</span><span style="color:#FF00FF;">"alert('登录成功!');parent.document.getElementById('login_ad').innerHTML='<font color=blue>"</span><span style="color:#0000CC;">.</span><span style="color:#0000FF;">$</span><span style="color:#008080;">showdata</span><span style="color:#0000CC;">.</span><span style="color:#FF00FF;">"</font>';"</span><span style="color:#0000CC;">;</span><br></li><li>&nbsp;&nbsp;&nbsp;&nbsp;<span style="color:#FF0000;">echo</span><span style="color:#FF00FF;">"";
}else{
    echo" "</span><span style="color:#0000CC;">;</span><br></li><li>&nbsp;&nbsp;&nbsp;&nbsp;<span style="color:#FF0000;">echo</span><span style="color:#FF00FF;">"alert('用户名或密码错误!');parent.document.getElementById('login_ad').innerHTML='<font color=red>登录失败！</font>';"</span><span style="color:#0000CC;">;</span><br></li><li>&nbsp;&nbsp;&nbsp;&nbsp;<span style="color:#FF0000;">echo</span><span style="color:#FF00FF;">"";
}
?>