Building a Simple Express.js Application

princepalkanpur007

Sunday, 2024-07-21

Express.js is a popular web application framework for Node.js that makes building robust and scalable server-side applications a breeze. In this tutorial, we’ll walk through the steps of creating a basic Express.js application from scratch. By the end, you’ll have a foundational understanding of how to set up and run an Express.js app.

1. Prerequisites

Before we begin, make sure you have the following installed:

Node.js (which includes npm, the Node.js package manager)
A code editor like Visual Studio Code or Sublime Text

2. Setting Up Your Project

First, create a new directory for your project and navigate into it:

mkdir my-express-app
cd my-express-app

Initialize a new Node.js project by running:

npm init -y

This command creates a package.json file with default settings.

3. Installing Express

Next, install Express.js using npm:

npm install express

This command adds Express to your project dependencies.

4. Creating the Application

Create a new file named app.js (or index.js) in your project directory:

touch app.js

Open app.js in your code editor and add the following code:

const express = require('express');
const app = express();
const port = 3000;

// Middleware to parse JSON bodies
app.use(express.json());

// Define a simple route
app.get('/', (req, res) => {
  res.send('Hello, world!');
});

// Start the server
app.listen(port, () => {
  console.log(`Server is running at http://localhost:${port}`);
});

5. Understanding the Code

const express = require('express'); – Imports the Express module.
const app = express(); – Creates an Express application.
app.use(express.json()); – Adds middleware to parse JSON request bodies.
app.get('/', (req, res) => { ... }); – Defines a route that responds with “Hello, world!” when accessed via GET request.
app.listen(port, () => { ... }); – Starts the server on the specified port and logs a message to the console.

6. Running Your Application

To start your Express.js application, run the following command:

node app.js

You should see the message "Server is running at http://localhost:3000" in your terminal.

Open your browser and navigate to http://localhost:3000. You should see the “Hello, world!” message.

7. Adding More Routes

You can define additional routes to handle different endpoints. For example, add the following routes to app.js:

// Route to handle GET requests to /about
app.get('/about', (req, res) => {
  res.send('This is the About page.');
});

// Route to handle POST requests to /data
app.post('/data', (req, res) => {
  const data = req.body;
  res.json({ receivedData: data });
});

8. Error Handling

To handle errors, you can add a middleware function at the end of your route definitions:

app.use((err, req, res, next) => {
  console.error(err.stack);
  res.status(500).send('Something went wrong!');
});

9. Conclusion

Congratulations! You’ve created a simple Express.js application. From here, you can explore more advanced features of Express.js, such as routing, middleware, and integration with databases. Express.js is a powerful framework that simplifies server-side development and helps you build scalable applications quickly.

Feel free to experiment with different routes and middleware to enhance your app. Happy coding!