**Course Title:** Modern JavaScript Programming: From Fundamentals to Full-Stack Development **Section Title:** Back-End Development with Node.js and Express **Topic:** Setting up a simple Express server and creating routes Express.js is a popular and lightweight Node.js web framework that provides a flexible way to build web applications. In this topic, we'll cover the basics of setting up a simple Express server and creating routes to handle HTTP requests. **Prerequisites** Before diving into this topic, make sure you have the following: * Node.js (version 14 or later) installed on your machine * npm (version 6 or later) installed on your machine * A basic understanding of Node.js and JavaScript **Setting up a Simple Express Server** To get started with Express, you'll need to install it using npm. Create a new project folder and initialize it with npm by running the following commands in your terminal: ```bash mkdir express-server cd express-server npm init -y ``` Next, install Express by running: ```bash npm install express ``` Create a new file called `app.js` and add the following code to get started with Express: ```javascript // Import the Express library const express = require('express'); // Create a new Express app const app = express(); // Define a port number for the server to listen on const port = 3000; // Start the server and listen for incoming requests app.listen(port, () => { console.log(`Server started on port ${port}`); }); ``` **Understanding the Code** Here's a breakdown of what's happening in the code: * We import the Express library using `const express = require('express');`. * We create a new Express app using `const app = express();`. * We define a port number for the server to listen on using `const port = 3000;`. * We use the `listen()` method to start the server and listen for incoming requests on the specified port. **Creating Routes** Routes are used to map URLs to specific handlers that generate responses. Let's create a simple route to handle a GET request to the root URL ('/'). Add the following code to `app.js`: ```javascript // Define a route for the root URL ('/') app.get('/', (req, res) => { res.send('Hello from Express!'); }); ``` Here's a breakdown of what's happening in the code: * We use the `get()` method to define a route for the root URL ('/'). * The second argument is a callback function that takes two parameters: `req` (the request object) and `res` (the response object). * We use the `send()` method to send a simple response back to the client. **Running the Server** To run the server, execute the following command in your terminal: ```bash node app.js ``` Open your web browser and navigate to `http://localhost:3000/` to see the response from the server. **Key Concepts** Here are the key concepts to take away from this topic: * Express is a lightweight Node.js web framework that provides a flexible way to build web applications. * Routes are used to map URLs to specific handlers that generate responses. * The `listen()` method is used to start the server and listen for incoming requests. * The `get()` method is used to define a route for a GET request. **Practical Takeaway** Try creating more routes to handle different types of requests (e.g., POST, PUT, DELETE). Experiment with different response methods (e.g., `send()`, `json()` , `redirect()`). **External Resources** For more information on Express.js, check out the official documentation: https://expressjs.com/ **What's Next?** In the next topic, we'll cover working with middleware and handling HTTP requests and responses. We'll explore the different types of middleware, learn how to write custom middleware, and see how to use built-in middleware functions in Express. **Leave a Comment/Ask for Help** If you have any questions or need help with anything, leave a comment below.