Express.js Fundamentals

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

// Middleware — runs before route handlers
app.use(express.json());           // parse JSON body
app.use(express.urlencoded({ extended: true })); // parse form data
app.use(cors());                   // enable CORS
app.use(morgan('dev'));            // request logging

// Routes
app.get('/users', (req, res) => { res.json(users); });
app.get('/users/:id', (req, res) => {
  const user = users.find(u => u.id === req.params.id);
  if (!user) return res.status(404).json({ error: 'User not found' });
  res.json(user);
});
app.post('/users', async (req, res) => {
  const user = await db.users.create(req.body);
  res.status(201).json(user);
});

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

import { Router } from 'express';
import { z } from 'zod';

const router = Router();

const ProductSchema = z.object({
  name: z.string().min(2).max(100),
  price: z.number().positive(),
  category: z.enum(['electronics', 'clothing', 'food']),
  stock: z.number().int().min(0),
});

// GET /api/products
router.get('/', async (req, res, next) => {
  try {
    const { category, minPrice, maxPrice, limit = 20 } = req.query;
    const products = await ProductService.findAll({ category, minPrice, maxPrice, limit });
    res.json({ data: products, count: products.length });
  } catch (error) {
    next(error); // pass to error middleware
  }
});

// POST /api/products
router.post('/', authenticate, authorize('admin'), async (req, res, next) => {
  try {
    const validated = ProductSchema.parse(req.body);
    const product = await ProductService.create(validated);
    res.status(201).json(product);
  } catch (error) {
    if (error instanceof z.ZodError) {
      return res.status(400).json({ errors: error.flatten() });
    }
    next(error);
  }
});

export default router;