Express.js Cheatsheet

Express.js is a fast, unopinionated web framework for Node.js. It provides minimal tooling for building web servers, APIs, and applications with routing, middleware, and request handling.

NOTE: Tested using the latest version at time of writing, v4.x

Basic Setup

Create an Express application.

const express = require('express');
const app = express();
const PORT = 3000;

app.listen(PORT, () => {
  console.log(`Server running on port ${PORT}`);
});

Routes

Define HTTP route handlers.

// GET request
app.get('/users', (req, res) => {
  res.json({ users: [] });
});

// POST request
app.post('/users', (req, res) => {
  res.status(201).json({ success: true });
});

Route Parameters

Access URL parameters.

// /users/123
app.get('/users/:id', (req, res) => {
  const userId = req.params.id;
  res.json({ userId });
});

Request Body

Parse JSON and form data.

// Parse JSON (built-in in Express 4.16+)
app.use(express.json());

// Parse URL-encoded data
app.use(express.urlencoded({ extended: true }));

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

Middleware

Use middleware functions.

// Application-level middleware
app.use((req, res, next) => {
  console.log('Request:', req.method, req.path);
  next(); // Continue to next middleware
});

Error Handling

Handle errors with middleware.

// Error handling middleware (must be last)
app.use((err, req, res, next) => {
  console.error(err.stack);
  res.status(500).json({ error: 'Something went wrong!' });
});

Static Files

Serve static files.

// Serve files from 'public' directory
app.use(express.static('public'));

Router

Organize routes with Router.

// routes/users.js
const router = express.Router();

router.get('/', (req, res) => {
  res.json({ users: [] });
});

module.exports = router;

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

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Express provides a minimal foundation for Node.js web applications. Add middleware and organize routes for scalable applications.

For full documentation, see https://expressjs.com