React TypeScript 16.8 How to make useEffect() async

You can use an IIFE (asynchronous anonymous function which executes itself) like so:

useEffect(() => {
    // Some synchronous code.

    (async () => {
        await doSomethingAsync();
    })();

    return () => {
        // Component unmount code.
    };
}, []);

Declaring the effect as async function is not recommended. But you can call async functions within the effect like following:

useEffect(() => {
  const genRandomKey = async () => {
    console.log(await ecc.randomKey())
  };

  genRandomKey();
}, []);

More here: React Hooks Fetch Data

You can use the use-async-effect package which provides a useAsyncEffect hook:

useAsyncEffect(async () => {
  await doSomethingAsync();
});