Koa.js is an expressive HTTP middleware framework for Node.js, designed by the team behind Express to be smaller, more modular, and more developer-friendly. Built from the ground up to embrace async/await and ES2015+ features, Koa eliminates callback hell and provides a clean middleware composition model through a stack-like cascade. Unlike Express, Koa ships with no bundled middleware, allowing you to pull in only what you need — a philosophy that keeps your application lightweight and gives you explicit control over the request-response lifecycle. The key insight: Koa's context object (ctx) encapsulates Node's request and response into one powerful API, and the async middleware cascade creates elegant, predictable control flow for handling HTTP traffic, errors, and transformations.
What This Cheat Sheet Covers
This topic spans 28 focused tables and 119 indexed concepts. Below is a complete table-by-table outline of this topic, spanning foundational concepts through advanced details.
Table 1: Core Application Setup
| Method | Example | Description |
|---|---|---|
const app = new Koa();app.listen(3000); | • Creates a new Koa application instance • exposes .use() to register middleware and .listen() to start the server | |
app.use(async (ctx, next) => { await next();}); | • Registers middleware to the stack • middleware executes in the order added and must call await next() to pass control downstream | |
const server = app.listen(3000); | • Starts HTTP server on specified port • shorthand for http.createServer(app.callback()).listen(port) |