建议你在 useEffect 内部定义异步函数:

I suggest you to define async function inside useEffect itself:

function useFetch (url) {
  const [data, setData] = useState(null);
  useEffect(() => {
    async function fetchFromAPI() {
      const json = await( await fetch(url) ).json();
      setData(json);
    }
    fetchFromAPI()
  },[url]);

  return data;
};

您可以从 doc faqs 在 useEffect 内部使用异步函数:

You can take a look at valid example from doc faqs which uses async function inside useEffect itself:

function ProductPage({ productId }) {
  const [product, setProduct] = useState(null);

  useEffect(() => {
    // By moving this function inside the effect, 
    // we can clearly see the values it uses.
    async function fetchProduct() {
      const response = await fetch('http://myapi/product' + productId);
      const json = await response.json();
      setProduct(json);
    }

    fetchProduct();
  }, [productId]); // ✅ Valid because our effect only uses productId
  // ...
}