Critical Patterns

Route Organization (REQUIRED)

// ✅ ALWAYS: Separate routes by resource // routes/users.js const router = express.Router();

router.get('/', usersController.list); router.get('/:id', usersController.getById); router.post('/', validate(createUserSchema), usersController.create); router.put('/:id', validate(updateUserSchema), usersController.update); router.delete('/:id', usersController.delete);

module.exports = router;

Error Handling (REQUIRED)

// ✅ ALWAYS: Centralized error handler app.use((err, req, res, next) => { console.error(err.stack);

const status = err.status || 500; const message = err.message || 'Internal Server Error';

res.status(status).json({ error: { message, status } }); });

// ✅ Async wrapper for async route handlers const asyncHandler = (fn) => (req, res, next) => Promise.resolve(fn(req, res, next)).catch(next);

Decision Tree

Need validation? → Use Joi or Zod middleware Need auth? → Use Passport.js or JWT middleware Need logging? → Use Morgan middleware Need CORS? → Use cors middleware Need rate limiting? → Use express-rate-limit

Commands

npm init -y npm install express npm install -D nodemon npm run dev