Code splitting in Redux with SSR

reducers.js

import { combineReducers } from 'redux';
import users from './reducers/users';
import posts from './reducers/posts';

// Inject the initial state for async loaded reducers
function injectState(reducers, preloadedState = {}) {
  return Object.keys(reducers).reduce((finalReducers, key) => {
    if (typeof reducers[key] === "function") {
      finalReducers[key] = (state = preloadedState[key], action) => reducers[key](state, action);
    }
    return finalReducers;
  }, {});
}

export default function createReducer(asyncReducers, preloadedState) {
  return combineReducers(injectState({
    users,
    posts,
    ...asyncReducers
  }, preloadedState));
}

routes.js

export default function createRoutes(store) {
  // ...

  const CommentsRoute = {
    // ...

    getComponents(location, callback) {
      require.ensure([
        './pages/Comments',
        './reducers/comments'
      ], function (require) {
        store.injectReducer({
          comments: require('./reducers/comments').default
        });
        callback(null, require('./pages/Comments').default);
      })
    }
  };

  // ...
}

store.js

import { createStore } from 'redux';
import createReducer from './reducers';

export default function configureStore(preloadedState) {
  let asyncReducers = {};
  const store = createStore(createReducer(), preloadedState);
  
  store.injectReducer = (reducer) => {
    const newReducers = {
      ...reducer,
      ...asyncReducers
    };
    if (Object.keys(newReducers).length !== Object.keys(asyncReducers).length) {
      asyncReducers = newReducers;
      store.replaceReducer(createReducer(asyncReducers, preloadedState));
    }
  };
  return store;
}