Don't set the state if an old promise resolves.

Easy way to make sure you don’t set the state if an old promise resolves when the prop changes or the component unmounts.

const [someState, setSomeState] = useState(null);
useEffect(() => {
  let current = true;
  fetchSomething(someProp).then(result => {
    if(current) {
      setSomeState(result)
    }
  })
  return () => { current = false }
}, [someProp])