Type `EffectCallback` – allow async functions?

When asynchronously downloading data in a useEffect() callback, it would be nice if we could use an async function (whose return value would be ignored).

// Currently:
const [data, setData] = useState<null | Data>(null);
useEffect(() => {
  downloadData()
  .then((newData: Data) => {
    setData(newData);
  });
});

// Wish:
const [data, setData] = useState<null | Data>(null);
useEffect(async () => {
  const newData = await downloadData();
  setData(newData);
});

Current type:

type EffectCallback = () => void | (() => void);

Suggestion:

type EffectCallback = () => (void | Promise<void> | (() => void));

[developit]

@rauschma I get the impression you may have been hinting at something dramatically simpler here though: could we adjust the TS types of useEffect / useLayoutEffect such that returning a Promise is allowed? I think this would be reasonable.

~Perhaps to make it clear the return value is unused, we could allow returning Promise<void>?~ Edit: now I see you suggested this in your original feature request. Consider that a +1 from me! PR it if you can spare the minute!

[JoviDeCroock]

After extensive discussion we’ve decided not to support this due to the risk of pitfalls