Express.js is a web application framework that runs on Node.js. It simplifies the process of building web applications and APIs by providing a range of powerful features, including robust routing, middleware support, and HTTP utility methods. Thanks to its modular design, you can expand its functionality through additional libraries and Node.js modules.

Key Features

• Middleware: Express.js makes use of middleware functions that have access to the request-response cycle. This allows for a variety of operations such as logging, authentication, and data parsing.

• Routing: The framework offers a flexible and intuitive routing system, making it easy to handle different HTTP request methods on various URLs.

• Templates: Integrated support for template engines enables the dynamic rendering of HTML content.

• HTTP Methods: It provides built-in methods for all HTTP requests, such as get, post, put, delete, simplifying request handling.

• Error Handling: Express streamlines error management, and its middleware functions can specifically handle errors.

• RESTful APIs: Its features such as request and response object chaining, along with HTTP method support, make it ideal for creating RESTful APIs.

Relationship with Node.js

Express.js is a web application framework specifically designed to extend the capabilities of Node.js for web development. Node.js, on the other hand, is a cross-platform JavaScript runtime environment that allows developers to build server-side and networking applications.

Express.js accomplishes this through a layer of abstractions and a more structured approach, which Node.js, by itself, doesn’t provide out of the box.

Code Example: Basic Express Server

Here is the Node.js code:

// Import required modules
const express = require('express');

// Create an Express application
const app = express();
const port = 3000;

// Define a route and its callback function
app.get('/', (req, res) => {
  res.send('Hello World!');
});

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