Node.js Lesson 9: Events, EventEmitter and Memory Leaks

Hello everyone, today we are going to talk about events, what exactly are they. Then we will move on to understand what are EventEmitters and how to use them. We will also learn about memory leaks and learn about ways of dealing with it.

What are Events

Whenever something happens in the Nodejs world, we call in an event. Let me give you an example for clarity. When a user opens a file, we say that an event has occurred. So the opening of the file is an event. Similarly, if a file is read by an operation, it will be said to be another event.

Nodejs comes with a bundled module “Events”, which can be used to create or watch for events. Creating events is called an emitting event and watching for this emitted event is referred to as listening to events. We can use this module to emit events and listen to them. It can also be used to perform different actions based on the name and payload of any occurred event. You can require this module simplify by:

const events = require('events');

This events module gives us EventEmitter which grants us a bunch of operations like emitting events, listening events and capturing event data, etc. Let’s learn more about EventEmitters in the section below.

What are EventEmitters and why we use them?

EventEmitter is an object provided by the events module. It binds a function with an event. This bound function is then used to handle the event and perform actions accordingly. We can emit events in any part of the application and have a function setup that listens to it.

Example: Suppose you have an application where you want to notify the admins of the website whenever a new user signs up. You can fire an event whenever a user joins and have an event handler set up that sends a notification the moment this event occurs. You will have to bind this handler to an event listener which will get invoked as soon the new user event is emitted.

Let’s talk about how we can create such an event handler in the next section.

How to Setup EventEmitter

Setting an EventEmitter requires four steps. First, we will emit an event with a unique name. Then, we will set up that watches for this event. The third step will be to set up a callback to capture data sent by the event. This comes very handy when we want to pass some user info along with the event. At last, we will set up a handler for error management. Let’s talk about this is details.

Step 1: Emitting Events

First, we will require EventEmitter and instantiate it. This will provide us with a bunch of methods.

We can use EventEmitter.emit() method to emit events. It takes the event name as the first argument and arguments after that can be used to pass data along with it.

const EventEmitter = require('events').EventEmitter;

const ee = new EventEmitter();

ee.emit("Boop", "An event has occured");

Step 2: Listen for Events

Next, we want to listen to the event we just created. There are two methods for doing so. We can either add an event listener or use the on() method provided by EventEmitter instance to listen to the event.

const EventEmitter = require('events').EventEmitter;

const ee = new EventEmitter();

ee.addListener('Boop', function (data){
  console.log(data);
});

// OR

ee.on('Boop', function (data){
  console.log(data);
});

ee.emit("Boop", "An event has occured");

Step 3: Capture Event Data

As we read in step 1, the second argument of the emit() method can be used to pass data. We call this data as payload. Any payload passed while emitting the event will be received as the first argument of the callback passed with EventEmitter.on(). Remember the example we discussed above? This is how we can pass the user information with name and email property and notify who joined.

const EventEmitter = require('events').EventEmitter;

const ee = new EventEmitter();

ee.on('New User', function (data){
  console.log(`A new user has joined with username ${data.username} and email ${data.email}`);
});
// A new user has joined with username Shad and email something@example.com

ee.emit("New User", { username: "Shad", email: "something@example.com"});

Note: Don’t forget to call removeListener() when you’re done with the event to avoid memory leak whenever you’re using addListener().

Step 4: Handle Errors

There are certain scenarios where an error might occur. One such case is when you emit an event that has no handler. This will make EventEmitter generate an exclusion that must be handled or the process will fail entirely. We don’t want this to happen.

Luckily, we can add an event handler for errors specifically before emitting any events and it will take care of all the error exclusions that might occur. Let’s see how:

ee.on('error', function (){
  console.log(`Something went wrong`);
});

That’s pretty much it. Next, we will talk about memory leaks and listener counts.

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

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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!

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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.

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• Founded: 2006

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