lottery-wheel | Draw a lottery wheel and animate

It doesn't matter if it's a class or a functional component. In either you can and should place their sub-components in render() (after adequate import, of course).

In your particular case, your Wheel component needs to get an existing DOM element (el attribute) to be rendered into, and your #wheel element is rendered after the Wheel initialization and doesn't exist yet during. The issue is ordering of functions (unfortunately for you, render() always comes last).

The simple solutions here would be: a) create a #wheel element in your index.html (not recommended since it interferes with the main React concept of rendering the whole App into one div); b) initialize your Wheel in a componentDidMount() (if you don't know about React lifecycle, read about it - quite fundamental) or its hook equivalent - those are simply executed after render():