store.js

// @flow

/**
 * Create the store with asynchronously loaded reducers
 */

import { createStore, applyMiddleware, compose } from 'redux'
import { Iterable, fromJS } from 'immutable'
import { routerMiddleware } from 'react-router-redux'
import createSagaMiddleware from 'redux-saga'
import createReducer from './reducers'

const sagaMiddleware = createSagaMiddleware()

export default function configureStore (initialState: Object = {}, history: Object) {
  // Create the store with two middlewares
  // 1. sagaMiddleware: Makes redux-sagas work
  // 2. routerMiddleware: Syncs the location/URL path to the state
  const middlewares = [
    sagaMiddleware,
    routerMiddleware(history)
  ]

  /* istanbul ignore if */
  if (process.env.NODE_ENV === 'development') {
    const createLogger = require('redux-logger')
    const stateTransformer = (state) => {
      if (Iterable.isIterable(state)) return state.toJS()
      else return state
    }
    const logger = createLogger({
      stateTransformer
    })
    middlewares.push(logger)
  }

  const enhancers = [
    applyMiddleware(...middlewares)
  ]

  // If Redux DevTools Extension is installed use it, otherwise use Redux compose
  const composeEnhancers =
    process.env.NODE_ENV !== 'production' &&
    typeof window === 'object' && window.__REDUX_DEVTOOLS_EXTENSION_COMPOSE__ ? window.__REDUX_DEVTOOLS_EXTENSION_COMPOSE__ : compose

  const store = createStore(
    createReducer(),
    fromJS(initialState),
    composeEnhancers(...enhancers)
  )

  // Extensions
  store.runSaga = sagaMiddleware.run
  store.asyncReducers = {} // Async reducer registry

  // Make reducers hot reloadable, see http://mxs.is/googmo
  /* istanbul ignore next */
  if (module.hot) {
    module.hot.accept('./reducers', () => {
      System.import('./reducers').then((reducerModule) => {
        const createReducers = reducerModule.default
        const nextReducers = createReducers(store.asyncReducers)

        store.replaceReducer(nextReducers)
      })
    })
  }

  return store
}