Hi,
I just need to know when exactly to use this?
Like, do I replace this:
ReactDOM.render(<App />, document.getElementById('root'));
with this now:
class App extends React.Component {
constructor(props) {
super(props);
}
render() {
return <div/>
}
};
// change code below this line
ReactDOMServer.renderToString(<App />);
TIA! 
Link to the challenge: