Vanilla Express / Express + co comparison

comparison.js

// my existing express app

app.use(myMiddleware);

function myMiddleware(req, res, next) {
  doSomething(next); // does something async + takes a callback
}

app.get('/', function(req, res, next) {
  getHomePageData(function(err, data) {
    if(err) return next(err);
    res.render('home', {data: data});
  });
});

// co-routine-ified

app.use(myMiddleware);

function* myMiddleware(req, res, next) {
  var err;
  try {
    yield doSomething(); // does something async + returns a promise or thunk
  } catch(e) {
    err = e;
  }
  next(err);
}

app.get('/', function(req, res, next) {
  co(function* () {
    var data = yield getData(); // returns a thunk or promise
    res.render('home', {data: data});
  });
});