Redux logger middleware: Transform Immutable objects into JSON

configureStore.js

import Immutable from 'immutable';
import { applyMiddleware, createStore } from 'redux';
import createLogger from 'redux-logger';

import rootReducer from './reducers';

const logger = createLogger({
  // Transform Immutable objects into JSON
  transformer: (state) => {
    const newState = {};
    for (let i of Object.keys(state)) {
      if (Immutable.Iterable.isIterable(state[i])) {
        newState[i] = state[i].toJS();
      } else {
        newState[i] = state[i];
      }
    }
    return newState;
  }
});

export default function configureStore(initialState) {
  return applyMiddleware(
    logger
  )(createStore)(rootReducer, initialState);
};