REDUX_DEVTOOLS_EXTENSION

app.js

import React from 'react';
import { BrowserRouter, Route, Switch } from 'react-router-dom';
import { createStore, applyMiddleware, compose } from 'redux';
import { Provider } from 'react-redux';
import createSagaMiddleware from 'redux-saga';
import rootReducer from 'reducers';
import rootSaga from 'sagas';

import MainContainer from 'components/Main/MainContainer';
import ThankYouContainer from 'screens/ThankYou/ThankYouContainer';
import Error404 from 'screens/Error404/Error404';

const sagaMiddleware = createSagaMiddleware();
const middleware = [sagaMiddleware];

/* eslint-disable no-underscore-dangle */
const composeEnhancers = window.__REDUX_DEVTOOLS_EXTENSION_COMPOSE__ || compose;
const store = createStore(rootReducer, /* preloadedState, */
  composeEnhancers(applyMiddleware(...middleware)));
/* eslint-enable */

sagaMiddleware.run(rootSaga);

const App = () => (
  <Provider store={store}>
    <BrowserRouter>
      <Switch>
        <Route path="/checkout" component={MainContainer} />
        <Route path="/confirm" component={ThankYouContainer} />
        <Route component={Error404} status={404} />
      </Switch>
    </BrowserRouter>
  </Provider>
);

export default App;