< mockra >

Convert Koa Middleware - 04 Jan 2016


If you’re using Koa 2.0, you’ve likely noticed that a lot of middleware is no longer compatible. Luckily, this is an easy fix, if not a bit ugly. If you haven’t run across this issue, then the error you’ll see is:

TypeError: Support for generators has been removed. See the documentation for
examples of how to convert old middleware
https://github.com/koajs/koa#example-with-old-signature

This is generated because with 2.0 Koa removed support for generators, so you’ll need to convert your middleware to a supported format. In our case, we’re going to convert the old generator middleware to use promises. We’ll do so with the koa-convert library.

You can install koa-convert with:

  npm install koa-convert --save

Here’s an example for converting old middleware using koa-jade and es6.

  const Koa = require('koa')
  const Jade = require('koa-jade')
  const convert = require('koa-convert')

  const app = new Koa()
  const jade = new Jade({
    viewPath: './views'
  })

  app.use(convert(jade.middleware))

  app.use(ctx => {
    ctx.render('index')
  })

  app.listen(3010)

The key lines we’re using to convert the middleware are:

  const convert = require('koa-convert')

  app.use(convert(jade.middleware))

If your application relies on several old libraries, then you can just use convert on each one.

  app.use(convert(jade.middleware))
  app.use(convert(serve('./views')))

Once you’ve converted all of your old generator middleware, you’re good to go!