How to avoiding callback hell in Node.js

Callback hell is a phenomenon that afflicts a JavaScript developer when he tries to execute multiple asynchronous operations one after the other. Some people call it to be the pyramid of doom.

Let’s have a look at an example of what we call callback hell.

doSomething(param1, param2, function(err, paramx){
    doMore(paramx, function(err, result){
        insertRow(result, function(err){
            yetAnotherOperation(someparameter, function(s){
                somethingElse(function(x){
                });
            });
        });
    });
});

Note- The above code is for demonstration and not a working code.

This is looking bad just from the skeleton itself. In real code you will obviously have other statements like if, for or some other operations along with these nested functions. Add those to the above code and it would get really messy and unmanageable.

Update: Added the amazing async-await after it’s release in Node.js 7.10.0

Pro Tip

Do not overload your functions. Most of the times it might be possible that the real problem you are facing is not the callback hell, rather it’s poorly written functions. In such cases, the solutions we will see below would structure your code but they won’t solve your real problem. So, as a rule of thumb, make your function do less, meaning write small functions that accomplish a single task.

Techniques for avoiding callback hell

There are multiple techniques for dealing with callback hell. In this tutorial, we will have a look at the below two in particular.

1. Using Async.js

2. Using Promises

3. Using Async-Await

Managing callbacks using Async.js

Async is a really powerful npm module for managing asynchronous nature of JavaScript. Along with Node.js, it also works for JavaScript written for browsers.

Async provides lots of powerful utilities to work with asynchronous processes under different scenarios.

Installation

npm install --save async

async.waterfall()
For our problem, we will be looking at two functions of async in particular. i.e async.waterfall`) and async.series().
Async Waterfall is useful when you want to execute some tasks one after the other and at the same time pass on the result from the previous task to the next.

async.waterfall() takes in an array of functions ‘tasks‘ and a final ‘callback‘ function which is called after all the functions in tasks have completed or a callback is called with an error.
Have a look below for a better understanding.

ASYNC WATERFALL

var async = require('async');
async.waterfall([
    function(callback) {
        //doSomething
        callback(null, paramx); //paramx will be availaible as the first parameter to the next function
        /**
            The 1st parameter passed in callback.
            @null or @undefined or @false control moves to the next function
            in the array
            if @true or @string the control is immedeatly moved
            to the final callback fucntion
            rest of the functions in the array
            would not be executed
        */
    },
    function(arg1, callback) {
        //doSomething else
      // arg1 now equals paramx
        callback(null, result);
    },
    function(arg1, callback) {
        //do More
        // arg1 now equals 'result'
        callback(null, 'done');
    },
    function(arg1, callback) {
        //even more
        // arg1 now equals 'done'
        callback(null, 'done');
    }
], function (err, result) {
    //final callback function
    //finally do something when all function are done.
    // result now equals 'done'
});

So using async.waterfall(), you would be writing you code vertically instead of indenting it horizontally and entering the pyramid of doom. Plus your code would be much more organized and easy to read.

async.series()
Async provides another function for handling execution in series, async.series(). Async series works in a similar way to Async waterfall, by executing functions in the array one after the other with the difference that it won’t pass the data from one function to another, instead when all the functions have completed their execution the result of the functions will be available in the final callback as an array. Similar to async.waterfall() in async.series() as well, when any of the functions is called with an error callback, no more functions in the array are executed and the final callback is immediately called with the value of the error. Have a look below for a clear picture.

ASYNC SERIES

var async = require('async');
async.series([
    function(callback){
        // do some stuff ...
        callback(null, 'one');
        /**
            The 1st parameter passed in callback.
            @null or @undefined or @false control moves to the next function
            in the array
            if @true or @string the control is immedeatly moved
            to the final callback fucntion with the value of err same as
            passed over here and
            rest of the functions in the array
            would not be executed
        */
    },
    function(callback){
        // do some more stuff ...
        callback(null, 'two');
    }
],
// optional callback
function(err, results){
    // results is now equal to ['one', 'two']
});

There are more cool functions availaible with the async module make sure you check them out and use it in your Node.js projects.
Visit the Github page here: Async.js Github

Managing callbacks hell using promises

Promises are alternative to callbacks while dealing with asynchronous code. Promises return the value of the result or an error exception. The core of the promises is the .then() function, which waits for the promise object to be returned. The .then() function takes two optional functions as arguments and depending on the state of the promise only one will ever be called. The first function is called when the promise if fulfilled (A successful result). The second function is called when the promise is rejected.
Let us see the structure of a typical promise.

PROMISES

var outputPromise = getInputPromise().then(function (input) {
    //handle success
}, function (error) {
    //handle error
});

Chaining promises

We can also chain promises, this is an equivalent alternative to nesting callbacks. There are two ways to chaining promises. Promises can be chained inside or outside the handlers (.then() function). Chaining promises outside the handle is much clean and easy to read but we may have to chain promises inside the handler if we want to use some parameter in our next handler which available in the scope of the previous handler. Although too much chaining inside the handler will again result in horizontal code which we are trying to avoid. We can also chain promises with a combination of inside and outside chains. As a general rule, I would recommend you to avoid chaining inside the handler.

Also, another good part about chaining promises is that we can also add a catch block at the end of the chain to catch any error that occurs in any of the about functions.

CHAINING PROMISES

return getUsername().then(function (username) {
    return getUser(username);
})
.then(function (user) { //example of chaining outside the handler
   return userPassword().then(function(password){
        /**
            example of chaining inside the handler,
            since we need to use the @user param
            from the previous handler scope
        */
        if(user.password !== password){
            //reject promise or throw error
            return;
        }
    });
})
.catch(function(e){
     //handle error
     console.log(e);
});

Creating a function that returns a Promise
To create a function that works with promises we can use the in-built Promise class.

const test = function(){
    return new Promise((resolve, reject)=>{
        setTimeout(() => {
            resolve('done');
        }, 10);
    });
}

//call it like this
test().then((resp)=>{
    console.log(resp);
})
.catch((e)=>{
    console.log(e);
});

A promise is considered successful if the value is returned with the resolve method and unsuccessful if it is returned with the reject method.

Changing callbacks to promises

There are a few good libraries for promises, we will look at the examples from the popular Kriskowal’s q promises library. Make sure you have q installed.

npm install --save q

CALLBACKS TO PROMISES

var fs = require('fs');
var Q = require('q');
var readFile = Q.nfbind(fs.readFile);
readFile("foo.txt", "utf-8").then(function (text) {
   //handle success
}, function(err){
   //handle error
});

Using Async Await

One of the best things to come out in Node.js recently is the async-await feature. Async await makes asynchronous code look like it’s synchronous. This has only been possible because of the reintroduction of promises into node.js. Async-Await only works with functions that return a promise.

Right now the best way to avoid callback hell is by using async-await in Node.js. Let’s understand it with an example.

ASYNC-AWAIT

const getrandomnumber = function(){
    return new Promise((resolve, reject)=>{
        setTimeout(() => {
            resolve(Math.floor(Math.random() * 20));
        }, 1000);
    });
}

const addRandomNumber = async function(){
    const sum = await getrandomnumber() + await getrandomnumber();
    console.log(sum);
}

addRandomNumber();
 

If you see above we have a function that returns us a random number after 1 sec. This function returns a promise. Using the await keyword we tell javascript to wait for the result before moving forward. But this await keyword only works within functions that are declared as async. When we declare a function as async, we are telling javascript to suspend the execution until the result arrives whenever it encounter the await keyword.

Now, in promises to handle error we could directly chain a catch block. How would you do it in the above case? Well, we can simply use a try-catch block.
So our example above will look like this…

ASYNC-AWAIT

const getrandomnumber = function(){
    return new Promise((resolve, reject)=>{
        setTimeout(() => {
            resolve(Math.floor(Math.random() * 20));
        }, 1000);
    });
}

const addRandomNumber = async function(){
    try {
        const sum = await getrandomnumber() + await getrandomnumber();
        console.log(sum);
    } catch (error) {
        //handle error
        console.log(error);
    }
}

addRandomNumber();

One more important thing to note is, whenever you declare a function as async that function will return a Promise

Conclusion

We have seen, how we can deal with the problem of callback hell in Node.js. There are a few more ways to solve the problem like using generators, modularization etc. But we feel that async library and promises are the two de-facto solutions for dealing with callback hell. But that was only until the arrival of async-await. With async-await here you should immediately start using it in your programmes to clean up and organize your code. However, remember what we discussed earlier, your core problem might just not be the callback hell, it could be poorly written functions. Make sure you keep your functions skinny and focused on a single task. You will learn more about async and promises only when you will use them. So make sure you try them out next time in your projects.

Thanks for reading !

#node #nodejs #javascript

What is GEEK

Buddha Community

NBB: Ad-hoc CLJS Scripting on Node.js

Nbb

Not babashka. Node.js babashka!?

Ad-hoc CLJS scripting on Node.js.

Status

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.

Requirements

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).

Usage

Install nbb from NPM:

$ npm install nbb -g

Omit -g for a local install.

Try out an expression:

$ nbb -e '(+ 1 2 3)'
6

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
"/private/tmp/test-script"
#js {:columns 216, :rows 47}
510
#js ["node_modules" "package-lock.json" "package.json" "script.cljs"]
#js [#js ["foo" "bar"]]
true
$ ls
node_modules
package-lock.json
package.json
script.cljs

Macros

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)
                                        body))))
            body
            binding-pairs)))

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)'
6
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.

Dependencies

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.

Classpath

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"

Reagent

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

ink-demo.cljs:

(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]))

Promesa

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]
  (js/Promise.
   (fn [resolve _]
     (js/setTimeout resolve ms))))

(defn do-stuff
  []
  (p/do!
   (println "Doing stuff which takes a while")
   (sleep 1000)
   1))

(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
3

Also see API docs.

Js-interop

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.

Examples

See the examples directory for small examples.

Also check out these projects built with nbb:

• c64core: retrocompute aesthetics twitter bot
• gallery.cljs: script to download walpapers from windowsonearth.org.
• nbb-action-example: example of a Github action built with nbb.

API

See API documentation.

Migrating to shadow-cljs

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

Build

Prequisites:

• babashka >= 0.4.0
• Clojure CLI >= 1.10.3.933
• 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/

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#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

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

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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

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