原生ajax样例

来个小样例，一看就明白！

var ajax = new XMLHttpRequest();                    
ajax.open('post','http://localhost:8080/kfjs2/user/query');
ajax.setRequestHeader("Content-type","application/x-www-form-urlencoded");
ajax.send('name=admin');
ajax.onreadystatechange = function () {
     if (ajax.readyState==4 &&ajax.status==200) {
    //成功响应
    alert(ajax.responseText);//输出json
    　}
}