node.js async series function's arguments

Question

I need to do the code like following:

function taskFirst(k, v) {
    console.log(k, v);
}

function taskSecond(k, v) {
    console.log(k, v);
}

function run() {
    var g1 = "Something";
    var g2 = "Something";
    var g3 = "Something";
    var g4 = "Something";

    async.series(
        [
            taskFirst(g1, g2),
            taskSecond(g3, g4)
        ],
        function(error, result){

        }
    );
}

What is the right way to pass custom variables and async.js callback function?

Prithee

Answer 1

You could do something like this:

function taskFirst(k, v, callback) {
    console.log(k, v);

    // Do some async operation
    if (error) {
        callback(error);
    } else {
        callback(null, result);
    }
}

function taskSecond(k, v, callback) {
    console.log(k, v);

    // Do some async operation
    if (error) {
        callback(error);
    } else {
        callback(null, result);
    }
}

function run() {
    var g1 = "Something";
    var g2 = "Something";
    var g3 = "Something";
    var g4 = "Something";

        async.series(
            [
                // Here we need to call next so that async can execute the next function.
                // if an error (first parameter is not null) is passed to next, it will directly go to the final callback
                function (next) {
                    taskFirst(g1, g2, next);
                },
                // runs this only if taskFirst finished without an error
                function (next) {
                    taskSecond(g3, g4, next);    
                }
            ],
            function(error, result){

            }
        );
}

Pustule

Answer 2

This answer to async's github issue has worked for me perfectly. https://github.com/caolan/async/issues/241#issuecomment-14013467

for you it would be something like:

var taskFirst = function (k, v) {
   return function(callback){
      console.log(k, v);
      callback();
   }
};

Blim

Thanks, I was missing that I needed to wrap the function and return it :) – Diviner

I needed to create a dynamic array of functions with parameters that I needed to give to async.series and your answer helped me in the right direction, thanks – Kagera

Answer 3

It can be as follows

function taskFirst(k, v) {
    console.log(k, v);
}

function taskSecond(k, v) {
    console.log(k, v);
}

async.series([
    function(callback) { 
        callback(null, taskFirst(g1, g2));
    },
    function(callback) { 
        callback(null, taskFirst(g3, g4));
    }
],function(error, result){

});

Victualer

This won't work. The callback is executed immediately so async will move on to the next function. You should pass the callback to your function and all execute it one your asynchronous work is complete. – Alliaceous

Yes - this answer assumes the code inside taskFirst is blocking. – Mcguigan

Answer 4

Better way.

const a1 = (a, callback) => {
    console.log(a, 'a1')
    callback()
}
const a2 = (a, callback) => {
    console.log(a, 'a2')
    callback()
}

const run = () => {
    async.series([
        a1.bind(null, 'asd'),
        a2.bind(null, 'asd2')
    ], () => {
        console.log('finish')
    })
}
run()

Prink