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Express Routing & Controllers

In the previous lesson, we created a basic server. But as your project grows, you can't put 100 different routes in a single server.js file. Routing allows us to split our application into small, manageable pieces.

1. The Anatomy of a Route​

A route in Express follows this structure: app.METHOD(PATH, HANDLER)

  • app: The instance of express.
  • METHOD: The HTTP verb (GET, POST, PUT, DELETE).
  • PATH: The URL on the server (e.g., /api/users).
  • HANDLER: The function that runs when the route is matched.

2. Route Parameters​

Sometimes parts of your URL are dynamic. For example, in https://codeharborhub.github.io/our-team/details/?member=ajay-dhangar, the "ajay-dhangar" part changes depending on the user. We handle this using Params.

// The colon (:) tells Express this part is a variable
app.get('/user/:username', (req, res) => {
  const name = req.params.username;
  res.send(`Viewing profile of: ${name}`);
});

3. Query Strings​

Query strings are the key-value pairs you see after a ? in a URL (e.g., /search?club=cricket&sort=new). These are optional and used for filtering or searching.

server.js
app.get('/search', (req, res) => {
  const { club, sort } = req.query;
  res.send(`Searching for ${club} sorted by ${sort}`);
});

4. The Express Router​

To keep our code clean, we use express.Router() to group related routes into separate files. This is how we organize large projects at the Hub.

Step 1: Create a route file​

routes/userRoutes.js
const express = require('express');
const router = express.Router();

router.get('/profile', (req, res) => res.send('User Profile'));
router.get('/settings', (req, res) => res.send('User Settings'));

module.exports = router;

Step 2: Use it in your main server​

server.js
const express = require('express');
const app = express();
const userRouter = require('./routes/userRoutes');

// All routes in userRouter will now start with /user
app.use('/user', userRouter);

5. Controllers: Separating Logic​

To be a professional "Master" developer, you shouldn't put your logic inside the route file. Instead, we use Controllers.

  • Route file: Defines the URL.
  • Controller file: Contains the function logic.

Example Structure:

controllers/userController.js
exports.getUserProfile = (req, res) => {
    // Logic to fetch user from database would go here
    res.json({ name: "Ajay", role: "Developer" });
};

Now, in your route file, you can import this controller:

routes/userRoutes.js
const userController = require('../controllers/userController');
router.get('/profile', userController.getUserProfile);

Practice: The Mini-Library API​

Try to create a router for a "Book" system:

  1. Create a bookRoutes.js file.
  2. Add a GET route for /all to see all books.
  3. Add a GET route for /:id to see a specific book by its ID.
  4. Link it to your server.js under the path /api/books.
HTTP Status Codes

When responding to a route, always send the correct status code.

  • 200: OK (Success)
  • 201: Created (Success after POST)
  • 404: Not Found
  • 500: Server Error
bookRoutes.js
const express = require('express');
const router = express.Router();

router.get('/all', (req, res) => {
  res.json([{ id: 1, title: "The Great Gatsby" }, { id: 2, title: "To Kill a Mockingbird" }]);
});

router.get('/:id', (req, res) => {
  const bookId = req.params.id;
  // In a real app, you'd fetch the book from the database
  if (bookId === "1") {  
    res.json({ id: 1, title: "The Great Gatsby" });  
  } else if (bookId === "2") {  
    res.json({ id: 2, title: "To Kill a Mockingbird" });  
  } else {  
    res.status(404).send("Book not found!");
  }
});

module.exports = router;