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Routing is a fundamental concept in web development that involves determining how an application responds to a client request to a particular endpoint, which is a URI (or path) and a specific HTTP request method (GET, POST, etc.). In Node.js, routing is typically handled using frameworks like Express.js, which simplifies the process significantly.

Key Concepts

Routes: Define the endpoints and the HTTP methods that your application will respond to.
Route Handlers: Functions that are executed when a specific route is matched.
Middleware: Functions that have access to the request object (req), the response object (res), and the next middleware function in the application’s request-response cycle.

Setting Up Routing in Node.js with Express

Step 1: Install Express

First, ensure you have Express installed in your project. If not, you can install it using npm:

npm install express

Step 2: Create a Basic Express Application

Create a file named app.js and set up a basic Express application:

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

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

Step 3: Define Routes

Add routes to handle different HTTP methods and paths. For example:

// GET request to the root URL (/)
app.get('/', (req, res) => {
  res.send('Hello, World!');
});

// GET request to /about
app.get('/about', (req, res) => {
  res.send('About Us');
});

// POST request to /contact
app.post('/contact', (req, res) => {
  res.send('Contact Us');
});

Step 4: Route Parameters

You can define route parameters to capture values in the URL:

// GET request with a route parameter
app.get('/user/:id', (req, res) => {
  const userId = req.params.id;
  res.send(`User ID: ${userId}`);
});

Step 5: Query Parameters

Handle query parameters using req.query:

// GET request with query parameters
app.get('/search', (req, res) => {
  const query = req.query.q;
  res.send(`Search Query: ${query}`);
});

Step 6: Using Middleware

Middleware functions can be used to handle requests before they reach the route handlers:

// Middleware to log request details
app.use((req, res, next) => {
  console.log(`${req.method} request for '${req.url}'`);
  next();
});

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

Practical Example

Let's create a small application with multiple routes and middleware:

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

// Middleware to log request details
app.use((req, res, next) => {
  console.log(`${req.method} request for '${req.url}'`);
  next();
});

// Home route
app.get('/', (req, res) => {
  res.send('Welcome to the Home Page');
});

// About route
app.get('/about', (req, res) => {
  res.send('About Us');
});

// User route with parameter
app.get('/user/:id', (req, res) => {
  const userId = req.params.id;
  res.send(`User ID: ${userId}`);
});

// Search route with query parameter
app.get('/search', (req, res) => {
  const query = req.query.q;
  res.send(`Search Query: ${query}`);
});

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

Exercises

Exercise 1: Create a New Route

Add a new route /services that responds with a list of services.
Add a new route /contact that responds with a contact form (just a simple message for now).

Solution

// Services route
app.get('/services', (req, res) => {
  res.send('Our Services: Web Development, Mobile App Development, SEO');
});

// Contact route
app.get('/contact', (req, res) => {
  res.send('Contact Us at [email protected]');
});

Exercise 2: Route with Parameters

Create a route /product/:id that responds with the product ID.
Create a route /category/:name that responds with the category name.

Solution

// Product route with parameter
app.get('/product/:id', (req, res) => {
  const productId = req.params.id;
  res.send(`Product ID: ${productId}`);
});

// Category route with parameter
app.get('/category/:name', (req, res) => {
  const categoryName = req.params.name;
  res.send(`Category: ${categoryName}`);
});

Common Mistakes and Tips

Forgetting to call next() in middleware: Always call next() to pass control to the next middleware or route handler.
Order of routes: Ensure that more specific routes are defined before more general ones to avoid unexpected behavior.
Error handling: Use middleware to handle errors and send appropriate responses.

Conclusion

Routing is a crucial part of building web applications with Node.js and Express. By understanding how to define routes, handle parameters, and use middleware, you can create robust and scalable applications. In the next module, we will dive deeper into handling HTTP requests and responses, which will further enhance your ability to build dynamic web applications.

Routing

Key Concepts

Setting Up Routing in Node.js with Express

Step 1: Install Express

Step 2: Create a Basic Express Application

Step 3: Define Routes

Step 4: Route Parameters

Step 5: Query Parameters

Step 6: Using Middleware

Practical Example

Exercises

Exercise 1: Create a New Route

Solution

Exercise 2: Route with Parameters

Solution

Common Mistakes and Tips

Conclusion

Node.js Course

Module 1: Introduction to Node.js

Module 2: Core Concepts

Module 3: File System and I/O

Module 4: HTTP and Web Servers

Module 5: NPM and Package Management

Module 6: Express.js Framework

Module 7: Databases and ORMs

Module 8: Authentication and Authorization

Module 9: Testing and Debugging

Module 10: Advanced Topics

Module 11: Deployment and DevOps

Module 12: Real-World Projects