// 封装示例：

     function ajax(url, method, params, done) {

       var xhr = null;

       method = method.toUpperCase();

       xhr = window.XMLHttpRequest ? xhr = window.XMLHttpRequest : xhr = new ActiveXObject('Microsoft.XMLHTTP');

       if (typeof params === 'object') {

         var tempArr = [];

         for (var key in params) {

           var value = params[key];

           tempArr.push(key + '=' + value);

         }

         params = tempArr.join('&');

       }

       // GET

       if (method === 'GET') {

         url += '?' + params;

       }

       xhr.open(method, url, false);

       // POST

       var data = null;

       if (method === 'POST') {

         xhr.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');

         data = params;

       }

       xhr.onreadystatechange = function () {

         if (this.readyState !== 4 && this.status !== 200) return false;

         ongone(this.responseText);

       }

       xhr.send(data);

     }

     // 调用示例：ajax('get','test.php',{id:123,},ongone)

38     ajax('GET', 'test.php', {}, ongone);

39

40     var ongone = function (res) {

41       console.log('1');

42       console.log('2');

43       console.log(res);

44       console.log('gone!');

45     }