Using express middleware in koa

Question

I have existing code which implements an express middleware. How can I use this middleware in a Koa application?

When I try to call app.use(expressMiddleware) in order to use the middleware in my Koa app, Koa complains that a generator function is required:

AssertionError: app.use() requires a generator function

So I guess that some kind of adapter or trick is needed here... ideas?

Answer 1

Also, you can try koa-connect: https://github.com/vkurchatkin/koa-connect

It looks quite straightforward:

var koa = require('koa');
var c2k = require('koa-connect');
var app = koa();

function middleware (req, res, next) {
  console.log('connect');
  next();
}

app.use(c2k(middleware));

app.use(function * () {
  this.body = 'koa';
});

app.listen(3000);

Answer 2

koa is incompatible with express middleware. (see this blog post for a detailed explaination, especially the part 'Better written middleware').

You could rewrite you middleware for koa. The koa wiki has a special guide for writing middleware.

The req and res that you would receive in an express middleware are not directly available in koa middleware. But you have access to the koa request and the koa response objects via this.request and this.response.