README.md

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In this lesson, we will create an HTTP server using Express.js.

Express.js is a fast and lightweight framework, used majorly for web application development. Express is built on top of Node.js. It is designed to develop websites, web apps, & API’s easily. With that being said, let's create our first ever Express application.

From this lesson onwards, we will gradually build a todo-management application, where you will be able to add tasks with a due date, and once you finish the task, you will be able to mark it as completed. It's as simple as that. With that being said, let's get started.

Installing Express.js

First, we will initialize node project using npm init. Then, to install the Express.js in that application, we will run the following command in the terminal:

npm install express --save

Once that process gets complete, open the project in VS Code.

Configuring the Express server

Node.js has a built-in http module as well as https module, to create an HTTP/HTTPS server. But the implementation process is kind of difficult. Whereas, Express wraps the built-in http module and provides a cleaner interface to create an HTTP web server.

First, create a new file called index.js, there we will create and configure our Express.js server.

const express = require('express')
const app = express()

app.get('/', function (request, response) {
  response.send('Hello World')
})

app.listen(3000)

In your terminal, start the server using the command:

node index.js

Then head on over to localhost:3000 in your browser, and you should see "Hello World" printed on the webpage.

That's Great!

Decoding the server configuration

Now, let's understand the above snippet, line by line.

const express = require('express');
const app = express();

Here, the first line requires the Express module that was installed via NPM, and the second line sets up our Express application. With this application (app), you can configure and add functionality to the server.

Then,

app.listen(3000)

The app.listen() function tells the server to start listening for connections on a particular port, in this case, port 3000. This is why we went to localhost:3000 to look at our Hello World example.

The last part is the route handler:

app.get('/', function (request, response) {
  response.send('Hello World')
})

This part is very important. Here, using the app.get() method, Express creates a route handler to listen for GET requests from a client. The first argument in this function is the route path. In this case, we’re listening for GET requests on localhost:3000/. If we wanted to listen for a POST request, then we would use app.post().

The second argument is a callback function that takes a request object and a response object. The request object contains information about the request that came from the client, for example: request headers, query parameters, request body, etc. The response object contains information that we want to send as a response back to the client.

Inside app.get(), the response.send('hello world'); function sends a response with content in the body of the response. In this case, the body contains the plain text hello world.

Alright! Now we know how to set up a route!