Express.js Cheat Sheet

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

app.get('/', (req, res) => res.send('Hello'));
app.post('/users', (req, res) => res.json(req.body));
app.put('/users/:id', handler);
app.delete('/users/:id', handler);

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

app.get('/posts/:year/:month', (req, res) => {
  const { year, month } = req.params;
});

// GET /search?q=hello&page=2
app.get('/search', (req, res) => {
  const { q, page = 1 } = req.query;
});

const router = express.Router();
router.get('/', listUsers);
router.post('/', createUser);
router.get('/:id', getUser);
app.use('/api/users', router);

app.use(express.json());          // Parse JSON body
app.use(express.urlencoded({ extended: true }));
app.use(express.static('public')); // Serve static files

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

app.use((err, req, res, next) => {
  console.error(err.stack);
  res.status(500).json({ error: err.message });
});
// Must have 4 params to be error handler

const auth = (req, res, next) => {
  if (!req.headers.authorization) return res.sendStatus(401);
  next();
};
app.get('/admin', auth, adminHandler);

res.json({ user });
res.status(201).json({ created: true });
res.sendStatus(204);  // No content

res.redirect('/login');
res.redirect(301, '/new-url');

res.download('/path/to/file.pdf');
res.sendFile('/absolute/path/to/file.html');
res.type('html').send('<h1>Hello</h1>');

res.set('X-Custom', 'value');
res.cookie('token', 'abc', { httpOnly: true, maxAge: 86400000 });
res.clearCookie('token');

const cors = require('cors');
app.use(cors({ origin: 'https://example.com' }));

const rateLimit = require('express-rate-limit');
app.use(rateLimit({ windowMs: 15 * 60 * 1000, max: 100 }));

const asyncHandler = (fn) => (req, res, next) =>
  Promise.resolve(fn(req, res, next)).catch(next);

app.get('/data', asyncHandler(async (req, res) => {
  const data = await fetchData();
  res.json(data);
}));

const { body, validationResult } = require('express-validator');
app.post('/users',
  body('email').isEmail(),
  body('name').trim().notEmpty(),
  (req, res) => {
    const errors = validationResult(req);
    if (!errors.isEmpty()) return res.status(400).json(errors.array());
  }
);