Event Emitters play a very important role in the Node.js ecosystem.
The EventEmitter is a module that facilitates communication/interaction between objects in Node. EventEmitter is at the core of Node asynchronous event-driven architecture. Many of Node’s built-in modules inherit from EventEmitter including prominent frameworks like Express.js.

The concept is quite simple: emitter objects emit named events that cause previously registered listeners to be called. So, an emitter object basically has two main features:

• Emitting name events.
• Registering and unregistering listener functions.

It’s kind of like a pub/sub or observer design pattern (though not exactly).

What we will be building in this tutorial:

• EventEmitter class

About this course

Hi, I'm Rajesh Pillai and I've been running a startup where we train freshers or interns from all fields to start a career in computer science, web development, data science etc.

What we have observed is that while they undergo training, they have to refer to multitude of documents, articles, books, blogs, videos to gauge the depth of a topic (which is good, but time consuming).

That’s where the idea of this course came into being, so that the participants can get a single point of reference to most of the major topics in the respective area of study. They still have to search, watch videos, read books, article etc, but then they can now do in a much more focussed manner.

NodeJS cannot be covered in one tutorial, and hence am splitting this into multiple tutorials and this is the course which collects all the tutorials in one place.

This course is going to be very detailed and I want ...

Lets begin with the hello world program.

Create a file called helloworld.js using your favorite Text Editor.

let hello = `Welcome to NodeJS Tutorial.  Hello World!`
console.log(“Welcome to NodeJS Tutorial”);

To run this code, open up a command shell/terminal and execute the following code.

node helloworld

The output will be a beautiful message starting at you on the screen.

Modules are reusable functionality. They can be a function, a class, an object or even just simple variables.

To import a module we use the require() function in node. Require function is globally available.

NOTE: New version of Node.js supports ES6 notation of import and export statements.

Let’s see some of the features of modules in the examples below. In global.js file:

var path = require("path");
console.log(`Full path: ${__filename} and filename is ${path.basename(__filename)}`);

The output of the above code, once you run the command: node global in your terminal, would be:

JavaScript traditionally didn’t had great support for binary data. So, the Node developers had to tackle this problem and primarily for performance reason and this is where the Buffer data type came into picture.

They are specifically also useful when working with TCP streams and file operations.

Buffers are raw allocations of the heap and contains binary data, which just consist of bits, i.e. o or a 1.

The buffer documentation is here https://nodejs.org/dist/latest-v9.x/docs/api/buffer.html

They are available globally and thus don’t need to be imported and can be treated like any other JavaScript type.

We will understand buffer by following the below activities.

• Creating Buffer from string
• Creating Buffer from an array
• Convert Buffer to JSON

The process object is globally available to every node module. It contains functionalities which allow us to interact with current process in the system.

The Process object also provides information about the runtime environment. In addition, standard input/output (I/O) occurs through process, we can also gracefully terminate a Node application and we can even signal when the Node event loop (We will discuss this) has finished a cycle.

This is also useful for building command line applications as we can capture all user parameters passed to the program which it has been invoked from the terminal.

The user provided parameters are available in the process.argv variable.

Let us create a small terminal program that passes a message to the module. Create a file called greeting.js

console.log("Total Arguments: ", process.argv.length);

Node basically has two kinds of streams, a readable stream and a writable stream. An example of a stream is a TCP socket that we can read from and write to, or a file that we can append or read from sequentially.

Example 1: Let us create a HTML5 video streaming server with Node and Express

Why do we need streaming? If we won’t then the entire video file will be downloaded to the client and loaded into memory which may or may not be good.

Imagine the video size to be 100’s of MB’s, in that case the network bandwidth etc will break the user experience.

Also, take this scenario. You have 8GB RAM on the server, but you have a 20GB video file on the drive and you would like to load that file?

Welcome to streaming!

With streams, the file stays on the disk and only ch...