useEffect Clean-Up Function Executes After Component is Removed

This behavior has changes in React version 17.0.x.

Clean-up function should execute when the component unmounts, and I've noticed in React v.17 by the time cleanup function executes, React referenced elements are no longer available.

Working example with React v.16
Example with React v.17

Notice unmountSuccessful logs before divRef in React v.17 example.

This is the only relevant change I noticed from the changelog.

If the behavior of useEffect clean-up has changed it should be reflected on the docs.

Code Snippet:

const App = () => {
  const divRef = React.useRef(null);
  
  React.useEffect(() => {
    console.log('divRef ::', divRef.current)
    return function cleanUp() {
      console.log('[cleanUp] divRef ::', divRef.current)
    }
  }, [])
  return (
    <div ref={divRef}>
      Open Browser's Console For Output
    </div>
  )
}

ReactDOM.render(
  <App />,
  document.getElementById('root')
);

const unmountApp = () => {
  console.log('unmounting root...')
  const node = document.getElementById('root');
  const unmountSuccessful = ReactDOM.unmountComponentAtNode(node);
  console.log('unmountSuccessful ::', unmountSuccessful)
};

window.setTimeout(unmountApp, 1500);

Comece pela documentação de React useEffect vinculada na issue e compare a redação sobre a limpeza com o comportamento do React 17 mostrado nos dois exemplos do CodePen. Leia o pull request do changelog vinculado referente à alteração relevante. Está concluído quando a documentação explicar com precisão quando a limpeza é executada e se os elementos referenciados continuam disponíveis.