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How to handle an async function that depends on multiple other async functions

How to handle an async function that depends on multiple other async functions

I have an asynchronous function that works with the result of two other async functions.

Till now what I was doing is that I write function2 in the callback function1 and function2 in the callback of function2

function1(callbackFunction() {
    function2(callbackFunction() {

Is there any other way to handle this. I work usually with JavaScript code in client side and in nodeJs.

My scenario is that for function2 I don’t need output from function1. In another words function1 and function2 are independent; but function3 is dependent on function1 and function2.

I want my function2 to run independent on function1 but function3 to run dependent on both functio1 and function2.

Is there anything like

when(funtion1.complete && funtion2.complete) {

Solution :

There are some good libraries to deal with orchestrating asynchronous functions. async and q (or other Promises/A libraries) help.

If function2 does not depend on the result of function1, you can execute them in parallel. Here’s how it looks using async (these examples assume that your callback has a function(err, result) signature, which is the defacto pattern for Node:

    function(callback) { function1(callback); },
    function(callback) { function2(callback); }
], function(err, values) {
    function3(values[0], values[1]);

If function2 depends on the result from function1, waterfall may be a better pattern:

    function(callback) { function1(callback); },
    function(result, callback) { function2(result, callback); },
    function(result, callback) { function3(result, callback); },

Personally, I like q, because you can pass promises around and do all kinds of nifty stuff. Here’s how this would look using that:

  .then(function(result) { return q.nfcall(function2); })
  .then(function(result) { return q.nfcall(function3); })
  .fail(function(err) {
      // If any of them fail, this is called.

Or if function1 and function2 can be done in arbitrary order:

q.all([q.nfcall(function1), q.nfcall(function2)])
 .then(function(values) { function3(values[0], values[1]); })
 .fail(function(err) {

Here is a solution that I baked. You can try a call manager to call the dependant functions

var func1 = function() {
    console.log("Dependant call ... " + 1);
var func2 = function() {
    console.log("Dependant call ... " + 2);
var func3 = function() {
    console.log("Dependant call ... " + 3);
var func4 = function() {
    console.log("Dependant call ... " + 4);

var CallManager = function(funcs_config) {
    var _this = this;

    _this.functions = funcs_config;
    _this.callAsynchronous = function(f) {
        if (f != undefined) {
            for (var i = 0; i < f.length; i++) {
                f[i].call(function() {

        for (var func in _this.functions) {
            if (_this.functions[func].length == 0) {
                //not dependent to any function
            } else {
                console.log('Calling....' + func);
                eval(func +'();');

    return _this;

var callManager = new CallManager({
    //dependency configuration
    func2: [func1], //func2 depends on func1
    func3: [func2],
    func4: [func1, func3] //func4 depends on both func1 and func3


With the current config provided above, when it is run the output is given as –

Dependant call ... 1
Dependant call ... 2
Dependant call ... 2
Dependant call ... 3
Dependant call ... 1
Dependant call ... 3
Dependant call ... 4
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