Backend Technologies · JavaScript / TypeScript
Express.js — Free Learning Resources
Free, printable resources for Express.js — practice problems, quick-reference cheatsheet, and an interview prep sheet. No sign-up required.
Express.js — Practice Worksheet
Structured exercises and problems to build hands-on Express.js skills. Work through key concepts step by step.
Express.js — Cheatsheet
One-page quick-reference for Express.js — key syntax, commands, patterns, and best practices at a glance.
Express.js — Interview Sheet
Top Express.js interview questions with concise answers. Get ready for any technical round with this focused prep sheet.
About Express.js
Express.js is the minimal and flexible Node.js web framework that provides a thin layer of features without obscuring Node.js itself. Its middleware-based pipeline architecture and unopinionated design make it the most downloaded Node.js framework, with over 30 million weekly npm downloads. Express is the E in the MEAN and MERN stacks.
Express.jsCheat Sheet — What's Covered
- ✓Middleware pipeline — request lifecycle and next() chaining
- ✓Routing — Router(), route parameters, query strings, and route grouping
- ✓Error handling — the four-argument (err, req, res, next) signature
- ✓Template engines (EJS, Pug) and static file serving with express.static
- ✓Security essentials — helmet, cors, rate limiting, and input validation
Frequently Asked Questions — Express.js
What is Express middleware and how does the pipeline work?
Middleware are functions with (req, res, next) signature. Express executes them in registration order. Call next() to pass control forward, next(err) to jump to error handlers, or end the cycle with res.send()/res.json(). Register with app.use() or on specific route methods.
How do you create a modular routing structure in Express?
Use express.Router() to create mini-apps with their own middleware and routes. Register routes on the router, then mount it: app.use('/api/users', userRouter). One Router per resource keeps route files focused.
How does Express error handling work?
Error middleware has four parameters: (err, req, res, next). Pass errors with next(err) from anywhere. Express skips regular middleware and goes straight to error handlers. Always define them last with app.use((err, req, res, next) => ...).
How does Express handle async route errors?
Express does not catch async errors automatically. Wrap async handlers in try/catch and call next(err), or use express-async-errors package which patches Express to handle unhandled rejections from async route handlers.
What security middleware should every Express app use?
helmet sets HTTP security headers. cors restricts cross-origin requests. express-rate-limit prevents brute force. express-validator sanitizes and validates input. Never trust req.body without validation, and always use HTTPS in production.
Who Is This For?
Node.js developers building REST APIs or web applications who want maximum flexibility to assemble their own middleware stack.