nodejs 眾所周知單執行緒，非同步io。

模型圖如下：

對於for迴圈來說寫起來非常麻煩，曾嘗試過閉包，es6，asnyc。

最終選擇了使用 eventproxy，具體是什麼東西，大家可以百度。用起來很方便，下面上一簡單個人親測程式碼示例：

var eventproxy = require('eventproxy');

var ep = new eventproxy();

               // list 結果集合

                ep.after('get_attendance_teacher', result.length, function (list) {
                   
                    res.json(list);
                });
                //for迴圈 io
                for (var i = 0; i < result.length; i++) {
                    var queryAttendance ={};
                    queryAttendance = {'userId':result[i]._id,"time" : {$gt:startDate, $lt:endDate}};
                    Attendance.find(queryAttendance, function(err, resultAttendance) {
                        if (err) {
                            console.log("db get attendance err::", err);
                            return;
                        }
                        ep.emit('get_attendance_teacher', resultAttendance);

                    }).sort({"name":1,'time':timeSort});

                }
            }

雙層for迴圈 簡單demo

var arr = [{name:'Jack'}, {name:'Mike'}];
            async.map(arr, function(item1, callback1) {
                    
                    var arr2 = [{name:'111'}, {name:'222'}];
                    async.map(arr2, function(item2, callback2) {
                        callback2(null, item1.name+item2.name+'!!!');
                    }, function(err,abc) {
                        console.log(111111111)
                        console.log(abc)
                        // jack111 jack222   
                        // 11111111
                        // mike111 mike222
                        callback1(null, abc);
                    });

            }, function(err,resultAll) {
                console.log(2222222)
                console.log(resultAll)
                // jack111 jack222   mike111 mike222
            });