server.js

const updateState = app => m => app.updateData(app.state.withMutations(m));
const cleanup = app => ::app.dispose;

export default function(apiUrl, gtmKey) {
  const api = apiFactory(apiUrl);
  const data = fromJS(appState);
  return async (req, res, next) => {
    try {
      const app = new Application(data);
      const routes = defRoutes(app);
      const location = req.url;
      const {redirectLocation, renderProps} = await match({routes, location});
      if (redirectLocation)
        return res.redirect(301, redirectLocation.pathname + redirectLocation.search);
      else if (error)
        return next(error);
      else if (renderProps == null)
        return res.status(404).send('Not found');
  
      const context = {location, params: renderProps.params, isActive: renderProps.history.isActive};
      await loadData(api, context, getAuthCookie(req, res))
        .then(updateState(app))
        .then(render(res, renderProps, gtmKey, app))
        .then(cleanup(app));
    }
    catch (err) {
      next(err)
    }
  };
};

Application class is almost identical to https://gist.github.com/rarous/60dc6aef71a31de8950c