Express.js: REST API schnell erstellen

Express ist das beliebteste Node.js Framework für APIs. Minimal, flexibel und mit riesigem Ökosystem. Hier lernen Sie die Grundlagen.

Projekt Setup

# Projekt erstellen
mkdir my-api && cd my-api
npm init -y

# Dependencies
npm install express
npm install --save-dev nodemon

package.json

{
  "name": "my-api",
  "scripts": {
    "start": "node src/index.js",
    "dev": "nodemon src/index.js"
  }
}

Minimale API

// src/index.js
const express = require('express');
const app = express();
const PORT = process.env.PORT || 3000;

// JSON Body Parser
app.use(express.json());

// Routen
app.get('/', (req, res) => {
  res.json({ message: 'Hello World!' });
});

app.get('/users', (req, res) => {
  res.json([
    { id: 1, name: 'Max' },
    { id: 2, name: 'Anna' }
  ]);
});

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

app.post('/users', (req, res) => {
  const { name, email } = req.body;
  res.status(201).json({ id: 3, name, email });
});

// Server starten
app.listen(PORT, () => {
  console.log(`Server läuft auf Port ${PORT}`);
});

Projektstruktur

my-api/
├── src/
│   ├── index.js          # Entry Point
│   ├── routes/
│   │   ├── index.js
│   │   ├── users.js
│   │   └── products.js
│   ├── controllers/
│   │   ├── userController.js
│   │   └── productController.js
│   ├── middleware/
│   │   ├── auth.js
│   │   └── errorHandler.js
│   ├── models/
│   │   └── User.js
│   └── config/
│       └── database.js
├── package.json
└── .env

Router Module

// src/routes/users.js
const express = require('express');
const router = express.Router();
const userController = require('../controllers/userController');

router.get('/', userController.getAll);
router.get('/:id', userController.getById);
router.post('/', userController.create);
router.put('/:id', userController.update);
router.delete('/:id', userController.delete);

module.exports = router;

// src/routes/index.js
const express = require('express');
const router = express.Router();

router.use('/users', require('./users'));
router.use('/products', require('./products'));

module.exports = router;

// src/index.js
const express = require('express');
const routes = require('./routes');

const app = express();
app.use(express.json());
app.use('/api', routes);
// Ergibt: /api/users, /api/products

Controller

// src/controllers/userController.js
const users = [
  { id: 1, name: 'Max', email: 'max@example.com' },
  { id: 2, name: 'Anna', email: 'anna@example.com' }
];

exports.getAll = (req, res) => {
  res.json(users);
};

exports.getById = (req, res) => {
  const user = users.find(u => u.id === parseInt(req.params.id));

  if (!user) {
    return res.status(404).json({ error: 'User nicht gefunden' });
  }

  res.json(user);
};

exports.create = (req, res) => {
  const { name, email } = req.body;

  if (!name || !email) {
    return res.status(400).json({ error: 'Name und Email erforderlich' });
  }

  const newUser = {
    id: users.length + 1,
    name,
    email
  };

  users.push(newUser);
  res.status(201).json(newUser);
};

exports.update = (req, res) => {
  const user = users.find(u => u.id === parseInt(req.params.id));

  if (!user) {
    return res.status(404).json({ error: 'User nicht gefunden' });
  }

  const { name, email } = req.body;
  if (name) user.name = name;
  if (email) user.email = email;

  res.json(user);
};

exports.delete = (req, res) => {
  const index = users.findIndex(u => u.id === parseInt(req.params.id));

  if (index === -1) {
    return res.status(404).json({ error: 'User nicht gefunden' });
  }

  users.splice(index, 1);
  res.status(204).send();
};

Middleware

Logging Middleware

// src/middleware/logger.js
module.exports = (req, res, next) => {
  console.log(`${new Date().toISOString()} ${req.method} ${req.url}`);
  next();
};

// Verwenden
app.use(require('./middleware/logger'));

Auth Middleware

// src/middleware/auth.js
module.exports = (req, res, next) => {
  const token = req.headers.authorization?.split(' ')[1];

  if (!token) {
    return res.status(401).json({ error: 'Token erforderlich' });
  }

  try {
    const decoded = jwt.verify(token, process.env.JWT_SECRET);
    req.user = decoded;
    next();
  } catch (err) {
    res.status(401).json({ error: 'Ungültiger Token' });
  }
};

// Verwenden
router.get('/profile', authMiddleware, userController.getProfile);

Error Handling

// src/middleware/errorHandler.js
module.exports = (err, req, res, next) => {
  console.error(err.stack);

  if (err.name === 'ValidationError') {
    return res.status(400).json({ error: err.message });
  }

  if (err.name === 'UnauthorizedError') {
    return res.status(401).json({ error: 'Nicht autorisiert' });
  }

  res.status(500).json({
    error: process.env.NODE_ENV === 'production'
      ? 'Interner Serverfehler'
      : err.message
  });
};

// Am ENDE registrieren
app.use(errorHandler);

Async Error Handler

// Wrapper für async Funktionen
const asyncHandler = (fn) => (req, res, next) => {
  Promise.resolve(fn(req, res, next)).catch(next);
};

// Verwendung
router.get('/users', asyncHandler(async (req, res) => {
  const users = await User.find();
  res.json(users);
}));

Validierung mit express-validator

npm install express-validator

const { body, validationResult } = require('express-validator');

router.post('/users',
  body('email').isEmail().withMessage('Ungültige E-Mail'),
  body('password').isLength({ min: 6 }).withMessage('Mindestens 6 Zeichen'),

  (req, res) => {
    const errors = validationResult(req);

    if (!errors.isEmpty()) {
      return res.status(400).json({ errors: errors.array() });
    }

    // User erstellen...
  }
);

CORS aktivieren

npm install cors

const cors = require('cors');

// Alle Origins erlauben
app.use(cors());

// Oder spezifisch
app.use(cors({
  origin: 'https://example.com',
  methods: ['GET', 'POST', 'PUT', 'DELETE'],
  credentials: true
}));

Weitere Informationen

• 🔧 REST API Best Practices
• 🔐 JWT Authentifizierung
• 📦 NPM Grundlagen