简单的 创建AJax的方法

// 简单的ajax对象
          var myAjax = {
            // XMLHttpRequest IE7+, Firefox, Chrome, Opera, Safari ；  ActiveXObject IE6, IE5
            xhr: window.XMLHttpRequest ? new XMLHttpRequest() : new ActiveXObject('Microsoft.XMLHTTP'),
            get: function(url, callback){
              this.xhr.open('get', url);
              this.onreadystatechange(callback, this.xhr);
              this.xhr.send(null);
            },
            post: function(url, data, callback){
              this.xhr.open('post', url);
              this.xhr.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');
              this.onreadystatechange(callback, this.xhr);
              this.xhr.send(data);
            },
            onreadystatechange: function(func, _xhr){
              _xhr.onreadystatechange = function(){
                if(_xhr.readyState == 4){
                  if (_xhr.status == 200){
                    func(_xhr.responseText);
                  }
                }
              }
            }
          };