Contrlled elemented example with functional components

[majidsajadi]

all of the examples are implemented using react class components and its hard to migrate theme to functional components.
for example Controlled elements Re-Flex example using ReactDOM.findDOMNode(this) which is deprecated and not usefull in the functional component.
also i cant find a way to translate the snippet below to useState hook. since useState is not sync anymore.

this.setState({
          size
        }, () => resolve())

[leefsmp]

this is more general React class to FC migration question rather than specific to that lib. I don't have time to rewrite the examples at the moment unfortunately.