Node.js: Express Framework and RESTful APIs

What is Express?

Express is a minimal, unopinionated web framework for Node.js that simplifies building servers, routing, and APIs on top of the core http module.

npm install express

A Basic Express Server

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

app.use(express.json()); // parse JSON request bodies

app.get('/', (req, res) => {
    res.send('Hello from Express!');
});

app.listen(3000, () => {
    console.log('Server running on http://localhost:3000');
});

Routing

Express maps HTTP methods and URL paths to handler functions.

app.get('/users', (req, res) => {
    res.json([{ id: 1, name: 'Alice' }]);
});

app.post('/users', (req, res) => {
    const newUser = req.body;
    res.status(201).json(newUser);
});

app.put('/users/:id', (req, res) => {
    res.json({ id: req.params.id, ...req.body });
});

app.delete('/users/:id', (req, res) => {
    res.status(204).send();
});

// Route parameters and query strings
app.get('/products/:category', (req, res) => {
    console.log(req.params.category);  // /products/electronics -> "electronics"
    console.log(req.query.sort);       // ?sort=price -> "price"
    res.send('OK');
});

Middleware

Middleware functions run between the request and the final handler — used for logging, authentication, parsing, error handling.

// Custom middleware: runs for every request
app.use((req, res, next) => {
    console.log(`${req.method} ${req.url}`);
    next(); // pass control to the next middleware/handler
});

// Middleware scoped to a specific route
function authenticate(req, res, next) {
    if (req.headers.authorization) {
        next();
    } else {
        res.status(401).json({ error: 'Unauthorized' });
    }
}

app.get('/admin', authenticate, (req, res) => {
    res.send('Welcome, admin!');
});

Building a RESTful API

REST (Representational State Transfer) is an architectural style where each URL represents a resource, and HTTP methods define the action on it.

const express = require('express');
const app = express();
app.use(express.json());

let books = [{ id: 1, title: 'Clean Code' }];

app.get('/api/books', (req, res) => res.json(books));

app.get('/api/books/:id', (req, res) => {
    const book = books.find(b => b.id == req.params.id);
    if (!book) return res.status(404).json({ error: 'Not found' });
    res.json(book);
});

app.post('/api/books', (req, res) => {
    const book = { id: books.length + 1, ...req.body };
    books.push(book);
    res.status(201).json(book);
});

app.put('/api/books/:id', (req, res) => {
    const index = books.findIndex(b => b.id == req.params.id);
    if (index === -1) return res.status(404).json({ error: 'Not found' });
    books[index] = { ...books[index], ...req.body };
    res.json(books[index]);
});

app.delete('/api/books/:id', (req, res) => {
    books = books.filter(b => b.id != req.params.id);
    res.status(204).send();
});

app.listen(3000, () => console.log('REST API running on port 3000'));

REST Best Practices

1. Use nouns, not verbs, in URLs (/books, not /getBooks)
2. Use proper HTTP status codes (200, 201, 400, 404, 500)
3. Version your API (/api/v1/books)
4. Return JSON consistently
5. Use plural resource names

Key Takeaway: Express simplifies routing and middleware on top of Node's http module. RESTful APIs map HTTP methods (GET/POST/PUT/DELETE) to CRUD operations on named resources, returning JSON with proper status codes.