ES6逐漸流行，用Promise物件封裝一個ajax請求，程式碼如下：

//地址，請求方式，引數,是否非同步，頭部資訊[待續]
function ajax(url,type,param,async,header) {
                return new Promise(function(resolve, reject) {
                    var req = new XMLHttpRequest();
                    req.onload = function() { 
                        if(req.status == 200 || req.status == 304) {
                            resolve(JSON.parse(req.response));
                        } else {
                            reject(Error(req.statusText));
                        }
                    };
                    req.onerror = function() {
                        reject(Error("Network Error"));
                    };
                    type == null || type.toUpperCase() == 'GET'?type='get':type='post';
                    param = formatParams(param);
                    param == null || param == ''?url:url=url+'?'+param;
                    async == null || async == true?async=true:async=false;
                    //設定表單提交時的內容型別，未完
                    //xhr.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
                    req.open(type,url,async);
                    req.send();
                });
                function formatParams(data) {
                    var _fpArr = [];
                    for (var _fpName in data) {
                  _fpArr.push(_fpName + "=" + data[_fpName]);
                    }
                    return _fpArr.join("&");
                };
            };
//呼叫
 

ajax('http://wthrcdn.etouch.cn/weather_mini','get',{citykey:101010100},true).then(function(response) {
                console.log('請求成功~');
                console.log(JSON.stringify(response));
            }, function(error) {
                console.error("Failed!", error);
            });

上面的例子只需建立一個Promise物件，呼叫它的resolve()和reject()以及then()方法，then()裡面也可以寫箭頭函式；

【注】如果大家要單獨封裝指定請求的方法，如get()和post()，只需把改下傳參和指定req.open(type,url,async)中的type型別即可