The Express.js server is a popular and lightweight web application framework for Node.js. It provides a robust set of features for building web applications and APIs, and it’s known for its simplicity and flexibility.

The basic structure of an Express.js application consists of creating an instance of the Express application, defining routes to handle different HTTP requests, and setting up middleware to process requests and responses.

Here’s a detailed explanation of how the Express.js server works, using HTML tags to illustrate the key concepts:

“`html

Express.js Server

First, let’s create an instance of the Express application:

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

Next, we can define routes to handle different HTTP requests:

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

    app.post('/api/users', (req, res) => {
      // Handle POST request to create a new user
    });
  

Finally, we can set up middleware to process requests and responses. For example, we can use the built-in bodyParser middleware to parse request bodies:

    const bodyParser = require('body-parser');
    app.use(bodyParser.json());
  

Once the Express application is set up, we can start the server and listen for incoming requests on a specific port:

    const port = process.env.PORT || 3000;
    app.listen(port, () => {
      console.log(`Server is running on port ${port}`);
    });
  

And that’s it! With these basic steps, we’ve created a simple Express.js server to handle HTTP requests and serve web applications or APIs.

“`

This HTML document walks through the key elements of an Express.js server, including creating the Express application, defining routes, setting up middleware, and starting the server. By using HTML tags to illustrate the code snippets, we can clearly explain and visualize each step in the process.

In summary, the Express.js server is a powerful and flexible framework for building web applications and APIs in Node.js. Its simplicity and ease of use make it a popular choice for developers, and it’s well-supported by a large community of contributors. If you’re looking to build web applications with Node.js, Express.js is definitely worth considering.