Express.js

Cards · 20

Initialize an Express application

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

Start the server on a specific port

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

Define a basic GET route

app.get('/users', (req, res) => res.send('Get all users'));

Define a basic POST route

app.post('/users', (req, res) => res.status(201).send('User created'));

Enable built-in JSON body parsing middleware

app.use(express.json());

Enable URL-encoded form data parsing middleware

app.use(express.urlencoded({ extended: true }));

Access route path parameters

app.get('/users/:id', (req, res) => res.send(req.params.id));

Access query string parameters

app.get('/search', (req, res) => res.send(req.query.q));

Send a JSON response

app.get('/api/data', (req, res) => res.json({ status: 'ok' }));

Set HTTP status code explicitly

app.get('/not-found', (req, res) => res.status(404).send('Resource not found'));

Serve static files from a directory

app.use('/static', express.static('public'));

Create and use custom middleware

app.use((req, res, next) => { console.log(req.method, req.url); next(); });

Define a global error handling middleware

app.use((err, req, res, next) => res.status(500).send(err.message));

Create a modular route handler using Router

const router = express.Router(); router.get('/', (req, res) => res.send('Home'));

Mount a modular router onto an app path

const usersRouter = require('./users'); app.use('/users', usersRouter);

Send a file as a response

app.get('/download', (req, res) => res.sendFile('/path/to/file.pdf'));

Redirect a request to another URL

app.get('/old-path', (req, res) => res.redirect(301, '/new-path'));

Set custom HTTP response headers

app.get('/custom', (req, res) => res.set('X-Custom-Header', 'Value').send('Done'));

Handle PUT requests to update resources

app.put('/users/:id', (req, res) => res.send(`Updated user ${req.params.id}`));

Handle DELETE requests to remove resources

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