Koa-connect NPM

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` middleware parameter

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

Usage

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);

Contributing

Developing

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.