koa2-connect

1.0.2 verified Sat Apr 25 auth: no javascript maintenance

A small utility (v1.0.2, last updated 2019) that adapts Connect/Express-style middleware (req, res, next) to work with Koa 2.x async middleware (ctx, next). Unlike koa-connect, koa2-connect is designed to better support streaming middleware like webpack-dev-middleware and webpack-hot-middleware. It is a stopgap for when Koa-native alternatives are unavailable; not recommended for new projects where Koa-native middleware exists.

Common errors

error Error: next is not a function ↓

cause Your Express middleware expects a next callback, but koa2-connect may not pass one in certain failure cases.

fix

Ensure the middleware is compatible with Connect/Express and always calls next().

error TypeError: Cannot read property 'status' of undefined ↓

cause The Express middleware tried to access res.status, but Koa's response object has a different API.

fix

Use only raw Node.js http methods (res.writeHead, res.end) and avoid Express-specific functions like res.status.

error ReferenceError: require is not defined ↓

cause You are using ESM (ES modules) and need to use import instead of require.

fix

Use dynamic import: const c2k = (await import('koa2-connect')).default;

Warnings

gotcha Express middleware must call next() to allow Koa middleware downstream to execute. ↓

fix Ensure your Express middleware invokes next() when done, or use a Koa-native alternative.

gotcha The module does not provide types; you may need to add your own type declarations. ↓

fix Install @types/koa2-connect if available, or declare module 'koa2-connect' { ... }.

deprecated Package is in maintenance mode with no updates since 2019. Known issues may not be fixed. ↓

fix Consider migrating to native Koa middleware or using koa-connect as an alternative.

gotcha Express middleware that relies on synchronous response methods (e.g., res.sendStatus) may not trigger Koa's error handling correctly. ↓

fix Use a Koa-native error handler or wrap errors manually using try/catch inside the Express middleware.

Install

npm install koa2-connect

yarn add koa2-connect

pnpm add koa2-connect

Imports

c2k
wrong
```
import c2k from 'koa2-connect'
```
correct
```
const c2k = require('koa2-connect')
```
No default ESM export; use CommonJS require or synthetic default import.
default
wrong
```
import { convert } from 'koa2-connect'
```
correct
```
const conv = require('koa2-connect')
```
The module exports a single function; named imports like convert are incorrect.
Promise
wrong
```
app.use(someExpressMiddleware)
```
correct
```
const c2k = require('koa2-connect'); app.use(c2k(someExpressMiddleware))
```
Directly using Express middleware without wrapping will break because Koa expects a different signature.

Quickstart

Wrap an Express-style middleware with c2k and use it in a Koa app.

const Koa = require('koa');
const c2k = require('koa2-connect');
const app = new Koa();

// Express-style middleware
function expressMiddleware(req, res, next) {
  res.writeHead(200, { 'Content-Type': 'text/plain' });
  res.end('Hello from Express');
  next();
}

app.use(c2k(expressMiddleware));
app.use((ctx) => {
  ctx.body = 'Koa response';
});

app.listen(3000);