old_contents: import { createStore, applyMiddleware } from 'redux';
  import thunk from 'redux-thunk';
  import reducer from './reducers';
  
  const middlewares = [ thunk ];
  if (__DEV__) {
    const logger = require('redux-logger');
    middlewares.push(logger({ level: 'info' }));
  }
  
  const finalCreateStore = applyMiddleware(...middlewares)(createStore);
  
  export default function configureStore(initialState) {
    return finalCreateStore(reducer, initialState);
  }
  
new_contents: import { createStore, applyMiddleware } from 'redux';
  import thunk from 'redux-thunk';
  import reducer from './reducers';
  
  const middlewares = [ thunk ];
  if (typeof __DEV__ !== 'undefined' && __DEV__) {
    const logger = require('redux-logger');
    middlewares.push(logger({ level: 'info' }));
  }
  
  const finalCreateStore = applyMiddleware(...middlewares)(createStore);
  
  export default function configureStore(initialState) {
    return finalCreateStore(reducer, initialState);
  }
  
subject: Handle global__DEV__