https://medium.com/@adrianmacneil/getting-started-with-koa-js-52d8852fa49d#.sxwol4ssb

server.js

import Koa from 'koa';
import Router from 'koa-router';

const koa = new Koa();
const app = new Router();

app.get('/:name', async (ctx) => {
  ctx.body = `Hello, ${ctx.params.name}!\n`;
});

koa.use(app.routes());
koa.listen(3000);