Backend Technologies · JavaScript / TypeScript
Koa — Free Learning Resources
Free, printable resources for Koa — practice problems, quick-reference cheatsheet, and an interview prep sheet. No sign-up required.
Koa — Practice Worksheet
Structured exercises and problems to build hands-on Koa skills. Work through key concepts step by step.
Koa — Cheatsheet
One-page quick-reference for Koa — key syntax, commands, patterns, and best practices at a glance.
Koa — Interview Sheet
Top Koa interview questions with concise answers. Get ready for any technical round with this focused prep sheet.
About Koa
Koa is a next-generation Node.js web framework designed by the team behind Express. It uses async/await throughout its middleware system instead of callbacks, eliminating the need for try/catch in every handler. Koa's minimal footprint (no bundled middleware) makes it ideal for building lean, composable HTTP servers.
KoaCheat Sheet — What's Covered
- ✓async/await middleware cascade — ctx, next(), and upstream/downstream flow
- ✓Context object (ctx) — request, response, state, and custom properties
- ✓Router setup with @koa/router — named routes and route params
- ✓Error handling with ctx.throw() and app.on('error', handler)
- ✓Popular middleware: koa-bodyparser, koa-static, koa-session, koa-cors
Frequently Asked Questions — Koa
How is Koa's middleware different from Express?
Koa uses async functions and true upstream/downstream flow. After all downstream middleware runs, control flows back up through each middleware — enabling clean post-processing (logging response time, setting headers). Express uses callbacks where next() only goes downstream.
What is the Koa context object?
ctx is a per-request object combining the Node.js request and response. ctx.request / ctx.response provide Koa's higher-level API. ctx.state is a plain object for passing data between middleware. Set ctx.body to send a response.
How do you handle errors in Koa?
Use ctx.throw(400, 'Bad Request') to throw HTTP errors. Wrap your app's middleware chain in an outer error-handling middleware using try/catch around await next(). Listen to app.on('error', handler) for unhandled errors that escape to the app level.
Does Koa include a router?
No — Koa has no router by default. Install @koa/router for routing: router.get('/users/:id', async ctx => { ctx.body = await getUser(ctx.params.id) }). Mount with app.use(router.routes()).use(router.allowedMethods()).
When would you choose Koa over Express or Fastify?
Choose Koa for a clean, modern async middleware stack with no legacy callback baggage. Choose Express for the widest middleware ecosystem. Choose Fastify for maximum throughput. Koa sits between: cleaner than Express, more flexible than Fastify.
Who Is This For?
Node.js developers who prefer async/await-first middleware architecture and want a lightweight base without Express's callback-based legacy.