middleware, how do i

koa.js

app.get('/participants', function*() {
  var options = {
    timestamp: {
      $gte: +(this.query.start || 0)
    }
  };
  return this.body = mustache.render(table_template, {
    participants: (yield participants.find(options))
  });
});

app.get('/participants.json', function*() {
  var options = {
    timestamp: {
      $gte: +(this.query.start || 0)
    }
  };
  return this.body = (yield participants.find(options));
});

app.get('/participants.csv', function*() {
  var options = {
    timestamp: {
      $gte: +(this.query.start || 0)
    }
  };
  return this.body = (yield json2csv({
    data: (yield participants.find(options))
  }));
});