来个小例子(ajax)

/*注册用户名检查小例子*/

<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>无标题文档</title>
<style>
   .box{
       margin:100px auto;
       text-align:center;}
</style>
</head>

<body>
   <div class="box">
        姓名:<input type="text" id="userName"/>
        密码:<input type="password" id="pass"/>
        <input type="button" value="注册" id="btn"/>
   </div>


<script>
//http://本机IP/AJAX/checkname   regname:要验证的用户名   注册时，即时验证用户名是否存在
       var userName = document.getElementById("userName");
       var pass = document.getElementById("pass");
       var oBtn = document.getElementById("btn");



userName.onblur = function(){
   var request;
   if(window.XMLHttpRequest){
       request = new window.XMLHttpRequest;
   }else{
       request = new ActiveXObject("MSxml12.XMLHTTP");
   }
   request.open("get","http://localhost?AJAX/checkname?regname"+"="+userName.value,true);

   request.readystatechange = function(){
       if(request.readyState == 4){
           if(request.status == 200){
               if(request.responseText = "yes"){
                   alert("用户名存在!不可用");
               }else{
                   alert("可用");
               }
           }
       }
   }
   request.send(null);
}

</script>
</body>
</html>