CODEWITHSUNDEEP
node.jsasynchronousasync.js
jsbisht
jsbisht

Reputation: 9649

Callback not getting called while using async.series

I have the following code, where i am calling a callback after my async task is completed:

var async = require("async");

function _callback(err, result){
    if(err) console.log('Error Occurred');
    console.log('Callback called');
    console.dir(result);
}

function tasks() {
    console.log('Start executing tasks');
    var tasks = [];
    var result = {};

    tasks.push(function(_callback) {
        console.log('Getting some data');
        _callback(null, result);
    });
    tasks.push(function(_callback) {
        console.log('Second function called');
        _callback(null, result);
    });

    async.series(tasks, function(){
        console.log('All done');
    });
}

tasks();

I have checked against the syntax expected in the async library. Code looks similar to me.

Can someone point out whats needs to be changed here.

Upvotes: 0

Views: 851

Answers (3)

Michael Tang
Michael Tang

Reputation: 4896

As it stands in your code right now, the _callback function you define above should never get called, as the _callback in the tasks functions is scope to the one passed by async.

// this will never get called
function _callback(err, result){
    if(err) console.log('Error Occurred');
    console.log('Callback called');
    console.dir(result);
}

function tasks() {
    console.log('Start executing tasks');
    var tasks = [];

    tasks.push(function(_callback) { // the _callback here overrides the one above for this closure
        console.log('Getting some data');
        _callback(null, result);
    });
    // ... more tasks

    async.series(tasks, function(){
        console.log('All done');
    });
}

If you want to reuse the logic in your _callback function, I'd recommend passing it the async callback as a parameter:

// rename some functions to avoid silly js scoping mysteries
function myCallback(err, result, asyncCallback){
    // shared logic here
    if(err) console.log('Error Occurred');
    console.log('Callback called');
    console.dir(result);

    asyncCallback(null, result);
}

// ...

tasks.push(function(asyncCallback) { // the _callback here overrides the one above for this closure
    console.log('Getting some data');
    myCallback(null, result, asyncCallback);
});
// ... more tasks

async wants its callback to be called so it knows when to continue, but that doesn't mean you can't intercept it with your own handlers :P.

Upvotes: 1

Jeff Sloyer
Jeff Sloyer

Reputation: 4964

You don't need the function call to _callback. You could simplify it like this.

var async = require("async");

function doSomeLogic(item, callback) {
    console.log(item);
    callback(null, item + 2);
}

function tasks() {
    console.log('Start executing tasks');
    var tasks = [];
    var result = {};

    tasks.push(function(callback){
        // do some more stuff ...
        callback(null, 'one');
    });

    tasks.push(function(callback){
        // do some more stuff ...
        callback(null, 'two');
    });


    async.series(tasks, function(error, results) {
        if (error) {
            console.log(error);
        }
        console.log(results);
        console.log('All done');
    });
}

tasks();

Upvotes: 0

Ben A.
Ben A.

Reputation: 488

Try it like this:

var async = require("async");

function _callback(err, result){
    if(err) console.log('Error Occurred');
    console.log('Callback called');
    console.dir(result);
}

function tasks() {
    console.log('Start executing tasks');
    var tasks = [];
    var result = {};

    tasks.push(function(next) {
        console.log('Getting some data');
        next(null, result);
    });
    tasks.push(function(_callback) {
        console.log('Second function called');
        next(null, result);
    });

    async.series(tasks, function(err, result){
        console.log('All done');
        _callback(err, result);
    });
}

tasks();

Async gives every single task a callback which you need to call to let async now that this task finished. After all tasks are finished you can call your callback. If you want your callback to get called after every single task is finished just add before every next(null, result) also an _callback(null, result) The reason that wouldn't work on your implementation is that you overwrite the global _callback method with the argument that has the same name.

Hope that makes sense :)

Upvotes: 1

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