08 – Exploring Async.js – async.retry

Source Code

In this tutorial, we’ll learn about how to retry async requests with async.retry

var async = require('async');

//Async example for Sign Up flow

    get_username: function(callback){
        console.log('in get_username');
        // async code to get some data
        callback(null, 'Zhi');
    connect_to_db: function(callback){
        console.log('in connect_to_db');
        var connected = true;  //set this to false here to simulate DB failure

        //Check connection
        if (connected) {
            callback(null, connected);
        } else {
            callback('Error connecting to DB', null);
    check_if_user_exist: ['get_username', 'connect_to_db', function(callback, results){
        console.log('in check_if_user_exist', JSON.stringify(results));
        //check if user exists in db...
        var userExists = false;

        if (userExists) {
            callback('User already exists in db', null);
        } else {
            setTimeout(function() {
                callback(null, userExists);
            }, 1000);

    sign_up: ['check_if_user_exist', function(callback, results){
        console.log('in sign_up', JSON.stringify(results));

        var username = results.get_username;
        var isDBConnected = results.connect_to_db;
        var userExists = results.check_if_user_exist;
        // console.log(username, isDBConnected, userExists);

        if (username && isDBConnected && !userExists) {
            callback(null, {'status': '200', 'msg':'Successfully signed up user'});
        } else {
            callback('Error signing up user', null);
    //retry([opts = {times: 5, interval: 0}| 5], task, [callback])
    //if you pass a number as first param, it will default times to that number, and interval to 0
    persist_to_db: ['sign_up', async.retry({times: 3, interval: 1000}, function(callback, results) {

    	console.log('trying to persist to db');
    	//Success: passing null to first parameter will signal a success attempt.
    	//callback(null, 'successfully persisted to DB');

    	//Failure: If API to DB failed for some reason, pass an error message to callback's first argument, and it will retry.
    	callback('failed to persist to db', null);
}, function(err, results) {
    console.log('error = ', err);
    console.log('results = ', results);


Comments Or Questions? Discuss In Our Discord

If you enjoyed this tutorial, make sure to subscribe to our Youtube Channel and follow us on Twitter @pentacodevids for latest updates!

More from PentaCode