ajax 验证用户名

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<META HTTP-EQUIV="expires" CONTENT="0">
<META HTTP-EQUIV="Pragma" CONTENT="no-cache">
<title>PHP+AJAX用户验证</title>
<style type="text/css">
<!--
body{
    text-align:center;
    font-family: Verdana, Arial, Helvetica, sans-serif;
    font-size: 12px;
    background:#EFEFEF;
}
#login {
    margin-top:6%;
    margin-right:auto;
    margin-left:auto;
    line-height: 20px;
    color: #000000;
    width:300px;
    border:1px solid #336699;
    background:#FFF;
}
#frmlogin{
    text-align:left;
    margin-left:8px;
}
h1{
    margin:0px 0px 10px 0px;
    padding:0px;
    width:100%;
    height:30px;
    line-height:30px;
    color:#FFF;
    background:#336699;
    font-size:18px;
    text-align:left;
    text-indent:10px;
    font-weight:normal;
    font-family:Arial, Helvetica, sans-serif;
}
input{
    border:1px solid #336699;
    height:14px;
    line-height:14px;
    width:120px;
}
.button{
    padding-right:10px;
    padding-left:10px;
    height:22px;
    line-height:22px;
    background:#fbfbfb;
    color:#000;
    text-align:center;
    border-right:2px solid #999;
    border-left:2px solid #999;
    border-top:1px solid #999;
    border-bottom:1px solid #999;
    margin-right:5px;
    margin-left:5px;
}
label{
    font-weight:bold;
    color:#336699;
}
#tip{
    color:#ff9900;
}
-->
</style>
<script type="text/javascript">
<!--
//XMLHttpRequest 
    var xmlhttp = false;
function createXMLHttpRequest(){
 if (window.XMLHttpRequest) { // Mozilla, Safari, ... 
  xmlhttp = new XMLHttpRequest();
 } else if (window.ActiveXObject) { // IE
  xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
 }
}
    function Ajax(data){  
  createXMLHttpRequest();
        xmlhttp.open("GET","db.php?username="+escape(document.getElementById("username").value),true);
        xmlhttp.send(null);
    
        xmlhttp.onreadystatechange=function(){
            if (4==xmlhttp.readyState){
                if (200==xmlhttp.status){
                    document.getElementById("tip").innerHTML=xmlhttp.responseText;
                }else{
                    alert("!");
                }
            }
        }
    }
    function chkUserName(obj){
        if(obj.value.length<1){
            obj.style.backgroundColor="#efefef";
            alert("不能为空!");
            obj.focus();
        }else{
            //Ajax,???
            Ajax(obj.value);
        }           

    }
//-->
</script>
</head>

<body>
    <div id="login">
        <h1>PHP+Ajax</h1>
        <form id="frmlogin" name="frmlogin">
          <label>用户名:
          <input name="username" type="text" id="username" size="22" maxlength="10" onblur="chkUserName(this)" />
          </label><label id="tip"></label>
                <p>
                  <label>密&nbsp;&nbsp;&nbsp;码:
                  <input name="pwd" type="password" id="pwd" size="24" maxlength="16" />
                  </label>
          </p>
                <p align="center">
                  <input name="Submit" type="button" class="button" id="btn_login" style="width:60px;background:#efefef;height:25px;line-height:25px;font-size:12px;" value="提交" />
                  <input name="Submit2" type="reset" class="button" style="width:60px;background:#EFEFEF;height:25px;line-height:25px;font-size:12px;" value="重设" />
                </p>
      </form>
        
</div>
</body>
</html>

db.php

<?php
    /*数据库连接*/
    
    ("数据库","名","密码");
    mysql_query("SET NAMES UTF8");
    mysql_select_db("test_4",$conn);
    
    //设置页面编码
    header("Content-type:text/html;charset=UTF-8");
    
    //查询数据库
    if(isset($_GET["username"])){
        $strsql="SELECT * FROM member WHERE username='".unescape($_GET["username"])."'";
        $result=mysql_query($strsql);
        );
        mysql_close($conn);
        
        //判断是否有此记录
        if(!$rows){
            echo "此用户名未被注册!";
        }else{
            echo "已被注册!";
        }
    }else{
        echo "别调戏我!";
    }
    
    /*PHP的unescape转换函数,用来转换Javascript用escape函数加密过的字符
    --此函数需要iconv函数库支持*/
    
    function unescape($str) {
        $str = rawurldecode($str);
        preg_match_all("/%u.{4}|&#x.{4};|&#d+;|&#d+?|.+/U",$str,$r);
        $ar = $r[0];
        foreach($ar as $k=>$v) {
            if(substr($v,0,2) == "%u")
                $ar[$k] = iconv("UCS-2","UTF-8",pack("H4",substr($v,-4)));
            elseif(substr($v,0,3) == "&#x")
                $ar[$k] = iconv("UCS-2","UTF-8",pack("H4",substr($v,3,-1)));
            elseif(substr($v,0,2) == "&#") {
                $ar[$k] = iconv("UCS-2","UTF-8",pack("n",preg_replace("/[^d]/","",$v)));
            }
        }
        return join("",$ar);
    }     
?>

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