koa-connect

Use Express/Connect middleware with Koa.

Warning

It is highly recommended to use a Koa-specific middleware instead of trying to convert an Express version when they're available. There is a non-trivial difference in the Koa and Express designs and you will inevitably run into some issues. This module is a workaround for the specific cases where the differences can be ignored. Additionally, it also enables library authors to write 1 version of their HTTP middleware.

Always use next

Express middlewares need to declare and invoke the next callback appropriately for the koa-connect integration to work correctly.

For library authors

If you're attempting to write a framework-agnostic middleware library, be sure to use only core HTTP methods and not any Express-dependent APIs like res.send.

Installation

npm install koa-connect@next

Usage

See examples/ for more real-world examples.

const Koa = require('koa')
const c2k = require('koa-connect')

// A generic Express-style middleware function
function connectMiddlware (req, res, next) {
  res.writeHead(200, {'Content-Type': 'text/plain'})
  res.end('From the Connect middleware')
  next()
}

// A generic Koa v2 middlware, without async/await
function koaMiddlware(ctx, next) {
  next()
    .then(() => {
      // The control flow will bubble back to here, like usual
    })
    .catch((err) => {
      // Error handling from downstream middleware, like usual
    })
}

// A generic Koa v2 middlware with async/await
async function koaMiddleware(ctx, next) {
  try {
    await next();
  } catch (e) {
    // Normal error handling
  }
  // Normal control flow
}

const app = new Koa()
app.use(koaMiddlware)
app.use(c2k(connectMiddlware))
app.use((ctx, next) => {
  console.log('It will continue on to here')
})

app.listen(3000)

Testing

Tests are in tests.js and are made with the Mocha framework. You can run them with npm test or npm run test:watch

License

MIT