窃喜，很简单嘛，读取输出。
好，开干。
var points = [ //事先导出来了
{ "userid" : 1022, "points" : 12 },
{ "userid" : 2592, "points" : 4 },
{ "userid" : 7304, "points" : 44 }
]
var saveData = [];
function readData(userid, callback){
db.collection('user').find({userid: userid}).toArray(function(error, data){
if(!error){
callback(data);
} else {
callback({});
}
});
} function write(data){
//file writing...
} var complete = 0;
function run(){
for(var i = 0; i < points.length; i++){
readData(points, function(data){
saveData.push({
userid: data.userid,
username: data.username,
usergender: data.usergender,
points: data.points
});
complete++;
if(complete == points.length){
write(data);
}
});
}
}
run();
结果可想而知，很多数据丢失，而且每次运行的结果都不一样——都是异步惹的祸，一拥而上，不死才怪
怎么让它一步步来呢？用Deferred写了个队列运行
function runQueueTasks(tasks){
var i = 0;
function run() {
if (!tasks[i]) {
return;
}
when(Deferred(tasks[i])).then(function() {
//run(); // May caught an RangeError: Maximum call stack size exceeded
setTimeout(run, 0); // ←nextTick ↑recursion
});
i++;
}
run();
}搞定，收工。
其中有一句setTimeout(run, 0)，我这里是为了避免递归溢出。
还有其它方面的资料可以自行搜索setTimeout 0，或参考setTimeout延时0毫秒的作用
可以试一下这两个函数：
function recursion(){
console.log("An RangeError will come very soon.");
recursion();
console.log("You won't see me.")
}
// RangeError: Maximum call stack size exceeded
function nextTick(){
console.log("Happy running.");
setTimeout(nextTick, 0);
console.log("The 2nd Happy running.");
}