AJAX 用户唯一性验证实现代码

从数据库my中的username用户表里验证：
checkusername.html：

复制代码代码如下:

 
<!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=gb2312" /> 
<title>无标题文档</title> 
</head> 
<script language="javascript"> 
var xmlHttp; 
function createXMLHttpRequest(){ 
if(window.ActiveXObject){ 
xmlHttp = new ActiveXObject("microsoft.XMLHTTP"); 
} 
else if(window.XMLHttpRequest){ 
xmlHttp = new XMLHttpRequest(); 
} 
} 
function send_request(url,data){ 
createXMLHttpRequest(); 
xmlHttp.open("POST",url,true); 
xmlHttp.onreadystatechange = check_lll; 
xmlHttp.setRequestHeader("CONTENT-TYPE", "application/x-www-form-urlencoded"); 
xmlHttp.send("username=" + data); 
} 
function check_lll(){ 
if(xmlHttp.readyState == 4){ 
if(xmlHttp.status == 200){ 
alert(xmlHttp.responseText); 
} 
} 
} 
function check_username(){ 
var f = document.form1; 
var username = f.username.value; 
if(username == ""){ 
alert("NULL"); 
return false; 
} 
else{ 
send_request("check_it.php",username); 
} 
} 
</script> 
<body> 
<form id="form1" name="form1" method="post" action=""> 
<p> </p><p> 
姓名： <input type="text" name="username" /> 
</p> 
<input type="button" value="check it" onclick="check_username()" /> 
<p> </p> 
<p>  </p> 
</form> 
</body> 
</html> 

check_it.php：

复制代码代码如下:

 
<?php 
$username = $_POST["username"]; 
$conn = mysql_connect("localhost:3306","root","123"); 
mysql_select_db("my",$conn); 
$sql = "select * from username where username = '$username'"; 
$result = mysql_query($sql,$conn); 
$num = mysql_fetch_array($result); 
if($num > 0){ 
printf("can't use"); 
} 
else{ 
printf("It can use"); 
} 

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