Let's create our first backend app with Express.js. Are you ready to get started?

Installing Express.js

Create a new directory for the app, and open the folder in the code editor. We are ready to start. In the terminal, run this command:

It's like ordering Express.js from a virtual app store, and npm is our delivery service.

As a result, we get such file-folder structure of our app:

Basic project structure:

• node_modules - Contains installed packages;
• package.json and package-lock.json- List project dependencies and scripts;
• app.js or index.js - Entry point for the Express application. We create it manually by ourselves.

🏗️ Build First Express App

Create a simple web server using Node.js and the Express.js framework. Follow the following steps:

Step 1: Import Express

As library we need firstly to import it to our file:

Step 2: Creating an Express Application Instance

We create an instance of the Express application. This app variable will be used to configure and define the web server's behavior.

Step 3: Set the Port

We define the port number that our server will listen on. In this case, it's set to 3000, but we can choose any available port number.

Step 4: Defining a Route

We set up a route for handling HTTP GET requests to the root URL (/). When a client (typically a web browser) accesses the server's root URL, it responds with Hello, World!.

• app.get('/') - This defines a route for handling GET requests to the root path (/). We can define routes for different HTTP methods (GET, POST, PUT, DELETE, etc.);
• (req, res) => { ... } - This is a callback function that gets executed when a client makes a GET request to the specified route. It takes two arguments: req (the request object) and res (the response object). In this case, it simply sends the Hello, World! text as the response.

Step 5: Start the Server

Let's start the server and make it listen on the specified port (in our case, port 3000). When the server is successfully started, it logs a message to the console, indicating which port it is listening on.

app.listen(port, ...) - This method starts the server and listens on the specified port. The second argument is a callback function that gets executed once the server is up and running.

Step 6: Run the App

We run the app in the terminal using node command.

🌐 After running the script

Our server will be running, and we can access it by opening a web browser and navigating to http://localhost:3000. You should see Hello, World! displayed in your browser.