Use Connect/Express middleware in Koa2

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2501.0.27 years ago7 years agoMinified + gzip package size for koa2-connect in KB


Base on koa-connect, improve to support webpack-dev-middleware and webpack-hot-middleware. 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.

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.


```sh npm install koa2-connect ```


See examples/ for more real-world examples. ```javascript const Koa = require('koa') const c2k = require('koa2-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) { return 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) ```


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