old_contents: import { createStore } from 'redux';
  import rootReducer from '../reducers'
  
  export default function configureStore(initialState) {
    const store = createStore(rootReducer, initialState);
  
    if (module.hot) {
      // Enable Webpack hot module replacement for reducers
      module.hot.accept('../reducers', () => {
        const nextReducer = require('../reducers').default;
        store.replaceReducer(nextReducer);
      })
    }
  
    return store;
  }
  
new_contents: import { createStore, compose } from 'redux';
  import rootReducer from '../reducers'
  
  export default function configureStore(initialState) {
    const store = createStore(rootReducer, initialState, compose(
      window.devToolsExtension ? window.devToolsExtension() : undefined
    ));
  
    if (module.hot) {
      // Enable Webpack hot module replacement for reducers
      module.hot.accept('../reducers', () => {
        const nextReducer = require('../reducers').default;
        store.replaceReducer(nextReducer);
      })
    }
  
    return store;
  }
  
subject: support redux dev tools chrome extension