Karim Aya

Karim Aya


Understanding Asynchronous Programming in Node.js

While Asynchronous programming comes with various features like faster execution of programs, it comes with a cost too i.e. usually it is a little bit difficult to program when compare to Synchronous programming.

This tutorial is about explaining each of the Asynchronous scenarios which you may face while coding. We will also learn about how to efficiently avoid callback hell situation.

Getting started

Consider following code.

var fs = require("fs");
var fileContent = fs.readFileSync('sync.js','utf8');
console.log("something else");

//Same code content
//something else

In above code, file has been read first and then console.log() executes.

Now consider following code.

var fs = require("fs");
    if(!err) {
console.log("something else");

Here output will be as follows :

something else
var fs = require("fs");
    if(!err) {
console.log("something else");

Here we have got console.log() content first and then file content. This is because code is Asynchronous and event loop executes that later.

This also covers one of the interview question where interviewer asks to write program to print same code.

What is callback hell

Familiar with something like this.

var fs = require("fs");
var db = require('somedbfile.js');
var sendEmail = require('someEmail.js');
    if(!err) {
    db.executeQuery('SELECT * FROM test',function(err,rows) {
      if(!err) {
      sendEmail(rows,function(err,data) {
        if(!err) {
        console.log("Operation done, i am in callback hell");

Note : Above code is just an example not a working code.

This happens due to the Asynchronous nature of the JavaScript. We want to execute tasks which are dependent on each other hence we wrap them into the callbacks of each function and hence caught into callback hell situation.

How to avoid callback hell

To avoid callback hell, follow one or combination of the following :

  • Modularise your code.
  • Use generators.
  • Use promises
  • Use event-driven programming.
  • Use Async.js

Modularise your code

Consider following code.

var fs = require("fs");
    if(!err) {

The callback function is a closure and can only be accessed inside the function. However you can create separate function by providing some name and pass that function as callback.

Like this.

var fs = require("fs");


function fileContent(err,data) {
  if(!err) {

The only drawback is you need to create lot of function as code grows.

Use generators

In simple words Generators provides you the ability to convert asynchronous code to synchronous one. Lets learn using example,consider following.

var fs = require("fs");
    if(!err) {
console.log("something else");

This is asynchronous code so console.log() will execute prior to readFile().

In order to avoid putting our console.log() inside the callback closure we can use generators to convert the asynchronous nature of readFile() into synchronous one.

Consider following code.

"use strict";
var fs = require('fs');
var co = require('co');

co(function* () {
  var file1 = yield readFile('demo.js');
  console.log("I am after file read even though its Async");

function readFile(filename) {
  return function(callback) {
    fs.readFile(filename, 'utf8', callback);

Try to execute this code, you will see the content of file first and then console.log().

I will cover generators in more detail in upcoming tutorials.

Use promises

Promise represents the result of asynchronous function. Promises can be used to avoid chaining of callbacks. In Node.js, you can use Q or Bluebird modules to avail the feature of promise.

If we want to convert file read code callback into promises here is how we can do that.

Make sure you have bluebird ( npm install bluebird ) installed.

var Promise = require('bluebird');
 // Converts all function of 'fs' into promises.
var fs = Promise.promisifyAll(require('fs'));

// 'then' when result comes.
.then(function(data) {
//'catch' when error comes.
.catch(function(err) {

Checkout bluebird API reference for more information.

Use event-driven programming

Node.js provides EventEmitter module that can help you to program using events. You can also use it to structure your code and avoid callback hell. However this may not help you in large structure code but it is an option.

Consider below code.

var EventEmitter = require('events').EventEmitter;
var emitter = new EventEmitter();
var fs = require('fs');
// Event to read file - generic function.
emitter.on('start_read',function(file_name) {
  console.log("Started Reading file....\n\n");
  fs.readFile(file_name, 'utf8', function (err,data) {
    if (err) {
      console.log("Error happens.");
    } else {
      console.log("File data", data);
// Let's read some file.

Here we have created one generic function which perform the file read. You can call this function by emitting events. You can also extend it to emit the events when file reading are done.

Use Async.js

Async.js is utility module provides various functions (around 70) to handle the Asynchronous JavaScript. This is most preferred way and recommended way by us.

Let’s look at some common situation which you may across while writing code and proposed solution for same using Async.js.

Scenario : Run multiple tasks that does not depend on each other and when they all finish do something else

In this scenario, we want to execute multiple asynchronous function which are not dependent on each other i.e We don’t need to block them.

Solution : Use async.parallel() function

Here is code to explain same.

var async = require('async');

    function(callback) {
      // Some Async task
    function(callback) {
      // Some Async task
  ],function(err,data) {
  // Code to execute when everything is done.

Scenario : Run multiple tasks one after another and once they are finish execute something else
No need to explain the scenario.

Solution : Use async.series() function

Here is code to explain same.

var async = require('async');

    function(callback) {
      // some async task
    function(callback) {
      // some async task
  ],function(err) {
    // Code to execute when everything is done.

Scenario : Run multiple tasks one after another and exchange data between them and once they are finish execute something else

This is the scenario very similar to above one except that we need to pass some data to the next function. Async.series() will pass each functions data to final callback function not to the next one.

Solution : Use async.waterfall() function

Here is code to explain same.

var async = require('async');

    function(callback) {
      // some code to execute
      // in case to go to next function provide callback like this.
      // Got some error ? Don't wanna go further.
      // Provide true in callback and execution will stop.
      //callback(true,"Some error");
    function(parameterValue,callback) {
      // Some code to execute.
      callback(null,"Some data");
  ],function(err,data) {
  // Code to execute after everything is done.

Run multiple parallel task for by iterating over array ( any collection ) and once all of them are finish execute something else

Consider a scenario where you need to send an email to 1000 users. You have email pushed in an array and you want to execute email() function independent of each other.

Solution : Use async.each()

Here is code to explain same.

var async = require('async');
var emails = ["abc@xyz.com","blahblah@aa.com"];

async.each(emails,function(singleEmail,callback) {
  // Emailer code
  // singleEmail will be one value at a time.
},function(err,data) {
  // Once all done, comes here.

Run multiple parallel task by iterating over array ( any collection ) in a set and once all of them are finish execute something else

Same scenario as mentioned above, instead we need limit by which we divide our data. Say you have 1 million email and you want to process 1000 emails at a time.

Solution : use async.eachLimit()

Here is code to explain same.

var async = require('async');
var emails = ["abc@xyz.com","blahblah@aa.com"];

async.eachLimit(emails,1000,function(singleEmail,callback) {
  // Emailer code
  // singleEmail will be one value at a time.
},function(err,data) {
  // Once all done, comes here.

Run multiple serial task for by iterating over array ( any collection ) and once all of them are finish execute something else

Same scenario as above, instead of going parallel we need to go for one task at a time.

Solution: You can either use async.eachLimit() with 1 as concurrency limit OR go for async.eachSeries()
Run multiple parallel task by iterating over array ( any collection ) and inside each parallel task run some tasks in series and once all of them are finish execute something else

Consider same email scenario, after sending an email you also need to update the database. That means you need to execute two task for each emails and that too in series manner by passing data from email() function to database one.

Use async.each() with async.waterfall()

Here is code to explain same.

var async = require('async');
var emails = ["abc@xyz.com","blahblah@aa.com"];

async.each(emails,function(singleEmail,callback) {
    function(callback) {
      // code to send email.
    function(emailSentOrNot,callback) {
      // Update DB.
  ],function(err,data) {
},function(err,data) {
  // Once all done, comes here.

Basically you can use any combination of async.js functions to fulfill your requirement. Here is some combination example.

var async = require('async');

},function(err,data) {
  // final callback

// going more deep.

      function(callback) {
          // You can use more combo here too.
        },function(err) {
          // final callback
          // Now call the callback of waterfall.
          callback(null,"No error");
    ],function(err,data) {
      // callback of top async.forEach()
},function(err) {
  // final callback

Performing Queue operation

Considering mass mailer in real world scenario, you cannot invoke like millions of callback function at one particular time and it is because of resource limitation and buffer.

In this kind of situation where operation should invoke in batch say 10000 emails at once and keep executing till everything is done you can use async.queue().

Here is very simple queuing example to send an Email. You can refer this tutorial for mailer code.

var async = require('async');

// Send email
var sendEmail = function(email,callback) {
  console.log("Sending email to "+email);

// create a queue object with concurrency 2
var q = async.queue(sendEmail,2);

// Called when every processing is done
q.drain = function() {
    console.log('all emails sent');

// add some emails to the queue

// add email to the front of the queue

Sending email to abc@gmail.com
Sending email to rwtc66@gmail.com
Sending email to shahid@codeforgeek.com
all emails sent

Wrapping up

We have covered some important and useful async.js function, however there are many more and you can surely use them according to your programming scenario.

If you come across any situation which we have not covered and you stuck on it, let us know in comments and we will surely look at it.


Async.js is no doubt very useful package for Node.js developer. It will save a lot of time and make your code looks good as well.

Learn More

#node-js #javascript

What is GEEK

Buddha Community

Understanding Asynchronous Programming in Node.js

NBB: Ad-hoc CLJS Scripting on Node.js


Not babashka. Node.js babashka!?

Ad-hoc CLJS scripting on Node.js.


Experimental. Please report issues here.

Goals and features

Nbb's main goal is to make it easy to get started with ad hoc CLJS scripting on Node.js.

Additional goals and features are:

  • Fast startup without relying on a custom version of Node.js.
  • Small artifact (current size is around 1.2MB).
  • First class macros.
  • Support building small TUI apps using Reagent.
  • Complement babashka with libraries from the Node.js ecosystem.


Nbb requires Node.js v12 or newer.

How does this tool work?

CLJS code is evaluated through SCI, the same interpreter that powers babashka. Because SCI works with advanced compilation, the bundle size, especially when combined with other dependencies, is smaller than what you get with self-hosted CLJS. That makes startup faster. The trade-off is that execution is less performant and that only a subset of CLJS is available (e.g. no deftype, yet).


Install nbb from NPM:

$ npm install nbb -g

Omit -g for a local install.

Try out an expression:

$ nbb -e '(+ 1 2 3)'

And then install some other NPM libraries to use in the script. E.g.:

$ npm install csv-parse shelljs zx

Create a script which uses the NPM libraries:

(ns script
  (:require ["csv-parse/lib/sync$default" :as csv-parse]
            ["fs" :as fs]
            ["path" :as path]
            ["shelljs$default" :as sh]
            ["term-size$default" :as term-size]
            ["zx$default" :as zx]
            ["zx$fs" :as zxfs]
            [nbb.core :refer [*file*]]))

(prn (path/resolve "."))

(prn (term-size))

(println (count (str (fs/readFileSync *file*))))

(prn (sh/ls "."))

(prn (csv-parse "foo,bar"))

(prn (zxfs/existsSync *file*))

(zx/$ #js ["ls"])

Call the script:

$ nbb script.cljs
#js {:columns 216, :rows 47}
#js ["node_modules" "package-lock.json" "package.json" "script.cljs"]
#js [#js ["foo" "bar"]]
$ ls


Nbb has first class support for macros: you can define them right inside your .cljs file, like you are used to from JVM Clojure. Consider the plet macro to make working with promises more palatable:

(defmacro plet
  [bindings & body]
  (let [binding-pairs (reverse (partition 2 bindings))
        body (cons 'do body)]
    (reduce (fn [body [sym expr]]
              (let [expr (list '.resolve 'js/Promise expr)]
                (list '.then expr (list 'clojure.core/fn (vector sym)

Using this macro we can look async code more like sync code. Consider this puppeteer example:

(-> (.launch puppeteer)
      (.then (fn [browser]
               (-> (.newPage browser)
                   (.then (fn [page]
                            (-> (.goto page "https://clojure.org")
                                (.then #(.screenshot page #js{:path "screenshot.png"}))
                                (.catch #(js/console.log %))
                                (.then #(.close browser)))))))))

Using plet this becomes:

(plet [browser (.launch puppeteer)
       page (.newPage browser)
       _ (.goto page "https://clojure.org")
       _ (-> (.screenshot page #js{:path "screenshot.png"})
             (.catch #(js/console.log %)))]
      (.close browser))

See the puppeteer example for the full code.

Since v0.0.36, nbb includes promesa which is a library to deal with promises. The above plet macro is similar to promesa.core/let.

Startup time

$ time nbb -e '(+ 1 2 3)'
nbb -e '(+ 1 2 3)'   0.17s  user 0.02s system 109% cpu 0.168 total

The baseline startup time for a script is about 170ms seconds on my laptop. When invoked via npx this adds another 300ms or so, so for faster startup, either use a globally installed nbb or use $(npm bin)/nbb script.cljs to bypass npx.


NPM dependencies

Nbb does not depend on any NPM dependencies. All NPM libraries loaded by a script are resolved relative to that script. When using the Reagent module, React is resolved in the same way as any other NPM library.


To load .cljs files from local paths or dependencies, you can use the --classpath argument. The current dir is added to the classpath automatically. So if there is a file foo/bar.cljs relative to your current dir, then you can load it via (:require [foo.bar :as fb]). Note that nbb uses the same naming conventions for namespaces and directories as other Clojure tools: foo-bar in the namespace name becomes foo_bar in the directory name.

To load dependencies from the Clojure ecosystem, you can use the Clojure CLI or babashka to download them and produce a classpath:

$ classpath="$(clojure -A:nbb -Spath -Sdeps '{:aliases {:nbb {:replace-deps {com.github.seancorfield/honeysql {:git/tag "v2.0.0-rc5" :git/sha "01c3a55"}}}}}')"

and then feed it to the --classpath argument:

$ nbb --classpath "$classpath" -e "(require '[honey.sql :as sql]) (sql/format {:select :foo :from :bar :where [:= :baz 2]})"
["SELECT foo FROM bar WHERE baz = ?" 2]

Currently nbb only reads from directories, not jar files, so you are encouraged to use git libs. Support for .jar files will be added later.

Current file

The name of the file that is currently being executed is available via nbb.core/*file* or on the metadata of vars:

(ns foo
  (:require [nbb.core :refer [*file*]]))

(prn *file*) ;; "/private/tmp/foo.cljs"

(defn f [])
(prn (:file (meta #'f))) ;; "/private/tmp/foo.cljs"


Nbb includes reagent.core which will be lazily loaded when required. You can use this together with ink to create a TUI application:

$ npm install ink


(ns ink-demo
  (:require ["ink" :refer [render Text]]
            [reagent.core :as r]))

(defonce state (r/atom 0))

(doseq [n (range 1 11)]
  (js/setTimeout #(swap! state inc) (* n 500)))

(defn hello []
  [:> Text {:color "green"} "Hello, world! " @state])

(render (r/as-element [hello]))


Working with callbacks and promises can become tedious. Since nbb v0.0.36 the promesa.core namespace is included with the let and do! macros. An example:

(ns prom
  (:require [promesa.core :as p]))

(defn sleep [ms]
   (fn [resolve _]
     (js/setTimeout resolve ms))))

(defn do-stuff
   (println "Doing stuff which takes a while")
   (sleep 1000)

(p/let [a (do-stuff)
        b (inc a)
        c (do-stuff)
        d (+ b c)]
  (prn d))
$ nbb prom.cljs
Doing stuff which takes a while
Doing stuff which takes a while

Also see API docs.


Since nbb v0.0.75 applied-science/js-interop is available:

(ns example
  (:require [applied-science.js-interop :as j]))

(def o (j/lit {:a 1 :b 2 :c {:d 1}}))

(prn (j/select-keys o [:a :b])) ;; #js {:a 1, :b 2}
(prn (j/get-in o [:c :d])) ;; 1

Most of this library is supported in nbb, except the following:

  • destructuring using :syms
  • property access using .-x notation. In nbb, you must use keywords.

See the example of what is currently supported.


See the examples directory for small examples.

Also check out these projects built with nbb:


See API documentation.

Migrating to shadow-cljs

See this gist on how to convert an nbb script or project to shadow-cljs.



  • babashka >= 0.4.0
  • Clojure CLI >=
  • Node.js 16.5.0 (lower version may work, but this is the one I used to build)

To build:

  • Clone and cd into this repo
  • bb release

Run bb tasks for more project-related tasks.

Download Details:
Author: borkdude
Download Link: Download The Source Code
Official Website: https://github.com/borkdude/nbb 
License: EPL-1.0

#node #javascript

Hire Dedicated Node.js Developers - Hire Node.js Developers

If you look at the backend technology used by today’s most popular apps there is one thing you would find common among them and that is the use of NodeJS Framework. Yes, the NodeJS framework is that effective and successful.

If you wish to have a strong backend for efficient app performance then have NodeJS at the backend.

WebClues Infotech offers different levels of experienced and expert professionals for your app development needs. So hire a dedicated NodeJS developer from WebClues Infotech with your experience requirement and expertise.

So what are you waiting for? Get your app developed with strong performance parameters from WebClues Infotech

For inquiry click here: https://www.webcluesinfotech.com/hire-nodejs-developer/

Book Free Interview: https://bit.ly/3dDShFg

#hire dedicated node.js developers #hire node.js developers #hire top dedicated node.js developers #hire node.js developers in usa & india #hire node js development company #hire the best node.js developers & programmers

Aria Barnes

Aria Barnes


Why use Node.js for Web Development? Benefits and Examples of Apps

Front-end web development has been overwhelmed by JavaScript highlights for quite a long time. Google, Facebook, Wikipedia, and most of all online pages use JS for customer side activities. As of late, it additionally made a shift to cross-platform mobile development as a main technology in React Native, Nativescript, Apache Cordova, and other crossover devices. 

Throughout the most recent couple of years, Node.js moved to backend development as well. Designers need to utilize a similar tech stack for the whole web project without learning another language for server-side development. Node.js is a device that adjusts JS usefulness and syntax to the backend. 

What is Node.js? 

Node.js isn’t a language, or library, or system. It’s a runtime situation: commonly JavaScript needs a program to work, however Node.js makes appropriate settings for JS to run outside of the program. It’s based on a JavaScript V8 motor that can run in Chrome, different programs, or independently. 

The extent of V8 is to change JS program situated code into machine code — so JS turns into a broadly useful language and can be perceived by servers. This is one of the advantages of utilizing Node.js in web application development: it expands the usefulness of JavaScript, permitting designers to coordinate the language with APIs, different languages, and outside libraries.

What Are the Advantages of Node.js Web Application Development? 

Of late, organizations have been effectively changing from their backend tech stacks to Node.js. LinkedIn picked Node.js over Ruby on Rails since it took care of expanding responsibility better and decreased the quantity of servers by multiple times. PayPal and Netflix did something comparative, just they had a goal to change their design to microservices. We should investigate the motivations to pick Node.JS for web application development and when we are planning to hire node js developers. 

Amazing Tech Stack for Web Development 

The principal thing that makes Node.js a go-to environment for web development is its JavaScript legacy. It’s the most well known language right now with a great many free devices and a functioning local area. Node.js, because of its association with JS, immediately rose in ubiquity — presently it has in excess of 368 million downloads and a great many free tools in the bundle module. 

Alongside prevalence, Node.js additionally acquired the fundamental JS benefits: 

  • quick execution and information preparing; 
  • exceptionally reusable code; 
  • the code is not difficult to learn, compose, read, and keep up; 
  • tremendous asset library, a huge number of free aides, and a functioning local area. 

In addition, it’s a piece of a well known MEAN tech stack (the blend of MongoDB, Express.js, Angular, and Node.js — four tools that handle all vital parts of web application development). 

Designers Can Utilize JavaScript for the Whole Undertaking 

This is perhaps the most clear advantage of Node.js web application development. JavaScript is an unquestionable requirement for web development. Regardless of whether you construct a multi-page or single-page application, you need to know JS well. On the off chance that you are now OK with JavaScript, learning Node.js won’t be an issue. Grammar, fundamental usefulness, primary standards — every one of these things are comparable. 

In the event that you have JS designers in your group, it will be simpler for them to learn JS-based Node than a totally new dialect. What’s more, the front-end and back-end codebase will be basically the same, simple to peruse, and keep up — in light of the fact that they are both JS-based. 

A Quick Environment for Microservice Development 

There’s another motivation behind why Node.js got famous so rapidly. The environment suits well the idea of microservice development (spilling stone monument usefulness into handfuls or many more modest administrations). 

Microservices need to speak with one another rapidly — and Node.js is probably the quickest device in information handling. Among the fundamental Node.js benefits for programming development are its non-obstructing algorithms.

Node.js measures a few demands all at once without trusting that the first will be concluded. Many microservices can send messages to one another, and they will be gotten and addressed all the while. 

Versatile Web Application Development 

Node.js was worked in view of adaptability — its name really says it. The environment permits numerous hubs to run all the while and speak with one another. Here’s the reason Node.js adaptability is better than other web backend development arrangements. 

Node.js has a module that is liable for load adjusting for each running CPU center. This is one of numerous Node.js module benefits: you can run various hubs all at once, and the environment will naturally adjust the responsibility. 

Node.js permits even apportioning: you can part your application into various situations. You show various forms of the application to different clients, in light of their age, interests, area, language, and so on. This builds personalization and diminishes responsibility. Hub accomplishes this with kid measures — tasks that rapidly speak with one another and share a similar root. 

What’s more, Node’s non-hindering solicitation handling framework adds to fast, letting applications measure a great many solicitations. 

Control Stream Highlights

Numerous designers consider nonconcurrent to be one of the two impediments and benefits of Node.js web application development. In Node, at whatever point the capacity is executed, the code consequently sends a callback. As the quantity of capacities develops, so does the number of callbacks — and you end up in a circumstance known as the callback damnation. 

In any case, Node.js offers an exit plan. You can utilize systems that will plan capacities and sort through callbacks. Systems will associate comparable capacities consequently — so you can track down an essential component via search or in an envelope. At that point, there’s no compelling reason to look through callbacks.


Final Words

So, these are some of the top benefits of Nodejs in web application development. This is how Nodejs is contributing a lot to the field of web application development. 

I hope now you are totally aware of the whole process of how Nodejs is really important for your web project. If you are looking to hire a node js development company in India then I would suggest that you take a little consultancy too whenever you call. 

Good Luck!

Original Source

#node.js development company in india #node js development company #hire node js developers #hire node.js developers in india #node.js development services #node.js development

Node JS Development Company| Node JS Web Developers-SISGAIN

Top organizations and start-ups hire Node.js developers from SISGAIN for their strategic software development projects in Illinois, USA. On the off chance that you are searching for a first rate innovation to assemble a constant Node.js web application development or a module, Node.js applications are the most appropriate alternative to pick. As Leading Node.js development company, we leverage our profound information on its segments and convey solutions that bring noteworthy business results. For more information email us at hello@sisgain.com

#node.js development services #hire node.js developers #node.js web application development #node.js development company #node js application

sophia tondon

sophia tondon


Top 10 NodeJs app Development Companies- ValueCoders

Node.js is a prominent tech trend in the space of web and mobile application development. It has been proven very efficient and useful for a variety of application development. Thus, all business owners are eager to leverage this technology for creating their applications.

Are you striving to develop an application using Node.js? But can’t decide which company to hire for NodeJS app development? Well! Don’t stress over it, as the following list of NodeJS app development companies is going to help you find the best partner.

Let’s take a glance at top NodeJS application development companies to hire developers in 2021 for developing a mind-blowing application solution.

Before enlisting companies, I would like to say that every company has a foundation on which they thrive. Their end goals, qualities, and excellence define their competence. Thus, I prepared this list by considering a number of aspects. While making this list, I have considered the following aspects:

  • Review and rating
  • Enlisted by software peer & forums
  • Hourly price
  • Offered services
  • Year of experience (Average 8+ years)
  • Credibility & Excellence
  • Served clients and more

I believe this list will help you out in choosing the best NodeJS service provider company. So, now let’s explore the top NodeJS developer companies to choose from in 2021.

#1. JSGuru

JSGuru is a top-rated NodeJS app development company with an innovative team of dedicated NodeJS developers engaged in catering best-class UI/UX design, software products, and AWS professional services.

It is a team of one of the most talented developers to hire for all types of innovative solution development, including social media, dating, enterprise, and business-oriented solutions. The company has worked for years with a number of startups and launched a variety of products by collaborating with big-name corporations like T-systems.

If you want to hire NodeJS developers to secure an outstanding application, I would definitely suggest them. They serve in the area of eLearning, FinTech, eCommerce, Telecommunications, Mobile Device Management, and more.

  • Ratings: 4.9/5.0

  • Founded: 2006

  • Headquarters: Banja Luka, Bosnia, and Herzegovina

  • Price: Starting from $50/hour

Visit Website - https://www.valuecoders.com/blog/technology-and-apps/top-node-js-app-development-companies

#node js developer #hire node js developer #hiring node js developers #node js development company #node.js development company #node js development services