spee.ch/react/client.js

import React from 'react';
import { hydrate } from 'react-dom';
import { Provider } from 'react-redux';
import { createStore, applyMiddleware, compose } from 'redux';
import { BrowserRouter } from 'react-router-dom';
import Reducer from 'reducers';
import createSagaMiddleware from 'redux-saga';
import rootSaga  from 'sagas';

import GAListener from 'components/GAListener';
import App from './app';

// get the state from a global variable injected into the server-generated HTML
const preloadedState = window.__PRELOADED_STATE__ || null;

// Allow the passed state to be garbage-collected
delete window.__PRELOADED_STATE__;

// create and apply middleware
const sagaMiddleware = createSagaMiddleware();
const middleware = applyMiddleware(sagaMiddleware);
const reduxMiddleware = window.__REDUX_DEVTOOLS_EXTENSION__ ? compose(middleware, window.__REDUX_DEVTOOLS_EXTENSION__()) : middleware;

// create teh store
let store;
if (preloadedState) {
  console.log('initial load: preloaded state found');
  store = createStore(Reducer, preloadedState, reduxMiddleware);
} else {
  console.log('initial load: no preloaded state found');
  store = createStore(Reducer, reduxMiddleware);
}

// run the saga middlweare
sagaMiddleware.run(rootSaga);

// render the app
hydrate(
  <Provider store={store}>
    <BrowserRouter>
      <GAListener>
        <App />
      </GAListener>
    </BrowserRouter>
  </Provider>,
  document.getElementById('react-app')
);