**Course Title:** Mastering Node.js: Building Scalable Web Applications **Section Title:** Working with the Express Framework **Topic:** Build a simple Express application with multiple routes and middleware functions.(Lab topic) **Objective:** By the end of this topic, you will be able to create a simple Express application with multiple routes and middleware functions. You will understand how to handle different HTTP requests and responses, and how to use middleware functions to enhance the functionality of your application. **Prerequisites:** You should have a basic understanding of Node.js, Express.js, and JavaScript. You should also have completed the previous topics in this course, including "Introduction to Node.js and Development Environment" and "Working with the Express Framework". **Step 1: Create a new Express application** To start, create a new directory for your project and navigate to it in your terminal or command prompt. Then, run the following command to create a new Express application: ```bash npm init -y npx express --view=ejs ``` This will create a new Express application with EJS as the view engine. **Step 2: Create multiple routes** In the `routes` directory, create a new file called `index.js`. This file will contain the routes for our application. Add the following code to `index.js`: ```javascript const express = require('express'); const router = express.Router(); router.get('/', (req, res) => { res.render('index', { title: 'Home Page' }); }); router.get('/about', (req, res) => { res.render('about', { title: 'About Page' }); }); router.get('/contact', (req, res) => { res.render('contact', { title: 'Contact Page' }); }); module.exports = router; ``` This code creates three routes: `/`, `/about`, and `/contact`. Each route renders a different EJS template. **Step 3: Create middleware functions** In the `middleware` directory, create a new file called `auth.js`. This file will contain a middleware function that checks if a user is authenticated before allowing them to access certain routes. Add the following code to `auth.js`: ```javascript const express = require('express'); const router = express.Router(); router.use((req, res, next) => { if (req.session.user) { next(); } else { res.redirect('/login'); } }); module.exports = router; ``` This code creates a middleware function that checks if a user is authenticated by checking if there is a `user` property in the `session` object. If the user is authenticated, the middleware function calls the `next()` function to continue to the next route. If the user is not authenticated, the middleware function redirects the user to the `/login` route. **Step 4: Use middleware functions in routes In the `routes` directory, open the `index.js` file and add the following code to use the `auth` middleware function: ```javascript const express = require('express'); const router = express.Router(); const auth = require('../middleware/auth'); router.get('/', auth, (req, res) => { res.render('index', { title: 'Home Page' }); }); router.get('/about', (req, res) => { res.render('about', { title: 'About Page' }); }); router.get('/contact', (req, res) => { res.render('contact', { title: 'Contact Page' }); }); module.exports = router; ``` This code uses the `auth` middleware function to check if a user is authenticated before allowing them to access the `/` route. **Step 5: Start the application** To start the application, run the following command in your terminal or command prompt: ```bash node app.js ``` This will start the Express application and make it available at `http://localhost:3000`. **Conclusion:** In this topic, you learned how to create a simple Express application with multiple routes and middleware functions. You also learned how to use middleware functions to enhance the functionality of your application. You can now use this knowledge to create more complex Express applications with multiple routes and middleware functions. **What's next:** In the next topic, you will learn about NoSQL databases and MongoDB. You will learn how to create a MongoDB database, add data to it, and query it using Mongoose. **Leave a comment or ask for help:** If you have any questions or need help with this topic, please leave a comment below. I will do my best to assist you. **External resources:** * Express.js documentation: <https://expressjs.com/> * EJS documentation: <https://ejs.co/> * MongoDB documentation: <https://docs.mongodb.com/> * Mongoose documentation: <https://mongoosejs.com/> Note: This topic is a lab topic, and you are expected to complete the exercises and code examples on your own. If you need help or have questions, please leave a comment below.