Installing Koa

Install Koa with npm, configure your package.json for ES modules, and run a "Hello World" HTTP server using ctx.body in under ten lines.

2 min read Level 1/5 #koa#install#setup

What you'll learn

Install Koa 2 with npm
Enable ES module mode via "type":"module" in package.json
Write and start a minimal Koa server that returns a text response

Getting a Koa server running takes three steps: create a project, install the package, and write a handful of lines.

Create the Project

mkdir my-koa-app
cd my-koa-app
npm init -y

Enable ES Modules

Koa 2 is an ES module package. Add "type": "module" to package.json so Node treats .js files as ESM:

{
  "name": "my-koa-app",
  "type": "module",
  "version": "1.0.0"
}

Install Koa

npm install koa

That is the only runtime dependency you need for a basic server — no bundled router, no body parser, nothing else installed automatically.

Hello World

Create server.js:

import Koa from "koa";

const app = new Koa();

app.use(async (ctx) => {
  ctx.body = "Hello, Koa!";
});

app.listen(3000, () => {
  console.log("Server running at http://localhost:3000");
});

Run it:

node server.js

Open http://localhost:3000 in your browser and you will see Hello, Koa!. Koa automatically sets the status to 200 and the Content-Type to text/plain when ctx.body is a string.

What Just Happened

app.use() registers a single middleware function. Because there is no router yet, every request — regardless of path or method — passes through this one function. Setting ctx.body tells Koa what to send back to the client.

Up Next

Explore the new Koa() application object and its key properties and methods.

The Application Object →