ajax+php异步传输用户注册检查

//js文件

//============判断是否为IE浏览器

var xmlHttp;

function S_xmlhttprequest() {

if(window.ActiveXObject) {

xmlHttp = new ActiveXObject('Microsoft.XMLHTTP');

} else if(window.XMLHttpRequest) {

xmlHttp = new XMLHttpRequest();

}

}

//=========================检查用户名方法

function checkName() {

var id_val=document.regFm.user.value;

if(id_val != ""){

S_xmlhttprequest();

xmlHttp.open("GET","check.php?id="+id_val,true);

xmlHttp.onreadystatechange = change;

xmlHttp.send(null);

}else{

var nameDiv=document.getElementById('check_name')

nameDiv.innerHTML="用户名不能为空";

}

}

function change() {

var nameDiv=document.getElementById('check_name')

  if(xmlHttp.readyState == 1) {

// nameDiv.innerHTML = "<img src='loading.gif'>";//等待进度条

}

    if(xmlHttp.readyState == 4 ){

if(xmlHttp .status == 200) {

var tt =  xmlHttp.responseText;

nameDiv.innerHTML = tt;

}

}

}

//检测 check.php

<?php

if($_GET[id]){

if(strlen($_GET[id])<6){

echo "<font color=red>用户名长度不能低于6个字符</font>";

}else{

//sleep(1);//等待执行mysql语句

$conn=mysql_connect('localhost','root','');

mysql_select_db('double',$conn) or die('连接失败');

mysql_query("set names 'GBK'");

$sql="SELECT * FROM `user_list` where `username`='$_GET[id]'";

$q=@mysql_query($sql);

if(is_array(mysql_fetch_row($q))){

echo "<font color=red>用户名已经存在</font>";

}else{

echo "<font color=green>可以使用</font>";

}

}

}

?>

//注册页面 reg.php

<script type="text/javascript" src="ajax.js"></script>

<form name="regFm" action="" method="post" enctype="text/plain">

  <h style="float:left">用户名：</h>

  <input style="float:left" type="text" name="user" onblur="checkName()"/>

  <span style="float:left" id="check_name"></span><br /><br />

  <button style="float:clear" name="submit"> 注册 </button>

  </form>