gurubot2/src/index.js

import '@babel/polyfill';

import React from 'react';
import { render } from 'react-dom';

import App from 'components/App';

function renderApp(AppComponent = App) {
    render(<AppComponent />, document.getElementById('root'));
}

if (process.env.NODE_ENV !== 'test') {
    renderApp();
}

if (module.hot) {
    // eslint-disable-next-line global-require
    module.hot.accept('./components/App', () => renderApp(require('components/App').default));
}