ExpressJS - Routing

Express.js - Scalable Routing

Routing is the process of determining how an application responds to a client request for a specific endpoint, which is a URI (or path) and a specific HTTP request method (GET, POST, etc.).

Basic Routing

The basic structure of a route in Express is:

app.METHOD(PATH, HANDLER)

• app is an instance of Express.
• METHOD is an HTTP request method in lowercase (e.g., get, post).
• PATH is the path on the server.
• HANDLER is the function executed when the route is matched.

Example: Basic Routes

import express from 'express';
const app = express();

// Responds to GET requests at the root URL
app.get('/', (req, res) => {
  res.send('Welcome to the homepage!');
});

// Responds to POST requests at '/api/users'
app.post('/api/users', (req, res) => {
  res.send('New user created!');
});

app.listen(3000);

Route Parameters

Route parameters are named URL segments used to capture values at specific positions in the URL. The captured values are populated in the req.params object.

// Route path: /users/:userId/books/:bookId
// Request URL: http://localhost:3000/users/101/books/42
// req.params will be: { "userId": "101", "bookId": "42" }

app.get('/users/:userId/books/:bookId', (req, res) => {
  const { userId, bookId } = req.params;
  res.send(`Fetching book with ID ${bookId} for user with ID ${userId}.`);
});

Scaling with express.Router

As your application grows, defining all routes in a single file becomes unmanageable. express.Router is a mini-Express application that allows you to group route handlers and middleware, keeping your code modular and organized.

Modern Project Structure for Routing

A common practice is to separate routes into their own files within a routes directory.

my-app/
├── src/
│   ├── routes/
│   │   ├── users.routes.js
│   │   └── products.routes.js
│   └── app.js           # Main app file
└── package.json

Example: Creating a User Router

First, define the user-related routes in src/routes/users.routes.js.

src/routes/users.routes.js

import express from 'express';

const router = express.Router();

// Note: The path here is relative to the path defined in app.js

// GET /api/users/
router.get('/', (req, res) => {
    res.json({ message: 'List of all users' });
});

// POST /api/users/
router.post('/', (req, res) => {
    res.status(201).json({ message: 'User created' });
});

// GET /api/users/:id
router.get('/:id', (req, res) => {
    res.json({ message: `Details for user ${req.params.id}` });
});

// Important: Export the router
export default router;

Mounting the Router in the Main App

Next, import and use this router in your main application file, src/app.js.

src/app.js

import express from 'express';
import usersRouter from './routes/users.routes.js';
// import productsRouter from './routes/products.routes.js'; // You would add other routers here

const app = express();
const PORT = 3000;

app.use(express.json()); // Middleware for parsing JSON

// Mount the routers
// All routes in usersRouter will be prefixed with '/api/users'
app.use('/api/users', usersRouter);
// app.use('/api/products', productsRouter);

app.get('/', (req, res) => {
    res.send('API is running...');
});

app.listen(PORT, () => {
    console.log(`Server listening on port ${PORT}`);
});

Benefits of Using express.Router

• Modularity: Keeps related routes together, making the code easier to understand and find.
• Maintainability: Changes to user-related endpoints only require modifying the users.routes.js file.
• Reusability: You can apply middleware specifically to one router, which will then apply to all routes defined within it.

By using express.Router, you create a clean, scalable, and professional structure for your Express applications, which is essential for any project beyond a simple demo.