Really? Hapi has its request lifecycle and built-in auth that makes auth much simpler than injecting authentication/authorization middlewares on every route.

Koa was created by the very same person as Express itself [https://github.com/tj] TJ Holowaychuk.

The initial idea is to do the next level express framework using back-then generator functions. What is missing ( for me ) is the smaller community and popularity. So it makes it tough to argue about the business impact between choosing koa over express.

Honestly, being a nodeJS freelancer for the last decade there was not a single project, where koa was in use. Mostly I've seen express or sailsjs [http://sailsjs.com] which is quite a full-blown MVC Rails style solution.

IMHO, and one of the reasons I decided to go with server, simplicity is a feature and the advantage of express over Koa. It is hard enough for new users to get started on Node.js, but to have to handle all of the new middleware concepts, PLUS to have to learn a lot more advanced features like generators is a no-go for my framework of choice.

- server: return something to reply to the browser. Can use `async` for more advanced features.

- express: reply.send() is fairly straightforward. next() for middleware is a new concept but conceptually in the right place (when you are digging a bit deeper in the middleware).

- Koa: yield, function with asterisk, etc.

So I think Koa is fine for devs who have been a while in JS dev, but the learning curve is too steep to get started. Same as what happens with React and the reason create-react-app has become so popular.