index.js

import React from 'react'
import ReactDOM from 'react-dom'
import './index.css'
import App from './components/App'
import registerServiceWorker from './registerServiceWorker'
import { createStore, applyMiddleware, compose } from 'redux'
import reducer from './reducers'
import { Provider } from 'react-redux'

const logger = store => next => action => {
    console.group(action.type)
    console.info('dispatching', action)
    let result = next(action)
    console.log('next state', store.getState())
    console.groupEnd(action.type)
    return result
}

const composeEnhancers = window.__REDUX_DEVTOOLS_EXTENSION_COMPOSE__ || compose

const store = createStore(
    reducer,
    composeEnhancers(
        applyMiddleware(logger)
    )
)

ReactDOM.render(
    <Provider store={store}>
        <App />
    </Provider>,
    document.getElementById('root')
)
registerServiceWorker();