Question on Client.js

[codestitch]

I'm a newbie and would like to ask regarding client.js code.

import React from 'react';
import ReactDOM from 'react-dom';
import { AppContainer } from 'react-hot-loader';
import { Provider } from 'react-redux';
import App from './containers/App';
import configureStore from './stores';

const store = configureStore();
ReactDOM.render(
<AppContainer>
<Provider store={store}>
<App />
</Provider>
</AppContainer>,
document.getElementById('app')
);

// what's the use of this?
if (module.hot) {
module.hot.accept('./containers/App', () => {
const NextApp = require('./containers/App').default; // eslint-disable-line global-require
ReactDOM.render(
<AppContainer>
<Provider store={store}>
<NextApp />
</Provider>
</AppContainer>,
document.getElementById('app')
);
});
}

What's the use of this one in module.hot?