在迭代完成之前，回调会触发

I'm using the async library in this project. One function (copied below) includes a nested loop to build a 2D Array. The callback is called before the array is completely built. I'd really like to understand why this is happening and learn more about best practices. What is the best way to solve this problem?

我在这个项目中使用异步库。一个函数（下面复制）包括用于构建2D数组的嵌套循环。在完全构建数组之前调用回调。我真的很想了解为什么会这样，并了解更多有关最佳实践的信息。解决这个问题的最佳方法是什么？

function getStopTimesForTrips(cb) {
        timeTable.listOfTripIds.forEach(function(id){
            retrieveTimesByTrip(id, function(err, st){
                var tempArray = [];
                st.forEach(function(st){
                    tempArray.push(st.arrival_time);
                });
                timeTable.stopTimes.push(tempArray);
            });
        });
        // cb(null, timeTable); <- This line fires the callback before we finish building the array. 
        setTimeout(function(){cb(null, timeTable);},2500); // This effective solution is poor form. What's the correct way to solve this issue? 
    }

2 个解决方案

#1

You don't seem to be using any function from the async library. The correct solution is to use async:

您似乎没有使用异步库中的任何函数。正确的解决方案是使用async：

async.each(timeTable.listOfTripIds,function(id,cb2){
    retrieveTimesByTrip(id, function(err, st){
        var tempArray = [];
        st.forEach(function(st){
            tempArray.push(st.arrival_time);
        });
        timeTable.stopTimes.push(tempArray);
        cb2(err); // Need to call this to tell async this iteration
                  // is done. Think of it as an async "return".
    });
},function(err){
    // if we're here it means the `async.each` is done:
    cb(null, timeTable);
});

2 个解决方案

#1

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