NodeJS, Async forEachSeries execution order

Question

Just trying to get my head around using Async module for NodeJS.

I have the following code.

var a1 = [1,2,3,4,5,6,7,8];
async.forEachSeries(a1, function(n1, callback) {
    console.log(n1);
    var a2 = [10,11,12,13,14];
    async.forEachSeries(a2, function(n2, callback) {
        console.log(n1 + " " + n2);
        callback();
    });
    callback();
});

I want to make the process of the above code in such a way that the print out becomes

1
1 10
1 11
1 12
1 13
1 14
2
2 10
2 11
2 12
2 13
2 14
3
3 10
3 11
3 12
3 13
3 14
.....

But instead I'm getting something like..

1
1 10
2
2 10
1 11
3
3 10
2 11
1 12
....

How do I fix this?

Answer 1

The forEachMethod also accepts a callback when everything done. So your code should look like this:

var a1 = [1,2,3,4,5,6,7,8];
async.forEachSeries(a1, function(n1, callback_s1) {
    console.log(n1);
    var a2 = [10,11,12,13,14];
    async.forEachSeries(a2, function(n2, callback_s2) {
        console.log(n1 + " " + n2);
        callback_s2();
    }, function () {
        /* Finished the second series, now we mark the iteration of first series done */ 
        callback_s1();
    } );
});

The problem in your code is the fact that you assume async.forEachSeries to be synchronous, but it is not. It guarantees the fact the array will be handled synchronously, but the function itself is asynchronous.