Use Express/Connect middleware with Koa.

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.

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

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.

npm install koa-connect

See examples/ for more practical usage.

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 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 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);

npm start starts the TypeScript compiler in watch mode. Code will be auto-formatted upon commit as part of the Prettier + lint-staged + Husky setup.

npm run build produces the types declaration file and JavaScript file for publishing.

npm test runs the tests. Tests are in tests.js and are made with the Mocha framework.

Use npm run test:watch in conjunction with npm start to automatically re-run the tests when the source changes.

MIT