<html>

<head>

<title>

ajax验证

</title>

</head>

<body>

<input type="text" name="username" id="username"/>

<input type="button" name="button" value="检测" onclick="validation();" />

<div id="info"></div>

<script>

function validation(){

    var name=document.getElementById('username').value;

    var data="username="+name+"&password="+pwd;

    ajax("verify.php",data,function(result){

        document.getElementById("info").innerHTML=result;

        });

}

function ajax(url,data,onsuccess){

    var xmlhttp=new XMLHttpRequest;

    xmlhttp.open("POST",url,true);

    xmlhttp.onreadystatechange = function(){

        if(xmlhttp.readyState==4){

            if(xmlhttp.status==200){

                onsuccess(xmlhttp.responseText);

            }else{

                alert("ajax错误");

            }

        }

    }

    xmlhttp.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');

    xmlhttp.send(data);

}

</script>

</body>

</html>

<?php

$con=@mysql_connect('localhost','root','');

$user=$_POST['username'];

mysql_query('use ms');

$sql = "select `username` from `user` where `username` = '$user'";

$res=mysql_query($sql);

$test=mysql_fetch_array($res);

if($test){

  echo "存在用户".$user;

}else{

  echo "不存在此用户".$user;

}

?>