我如何在 React 中运行另一个 function ？

Question

In my code, I have loadData() and useFilter() . I tried to run loadData() first as productsData need to be set for useFilter() to process productsData . However, I tried .then() but it still gives me undefined when I console log useFilter() How do I fix this?

  const [productsData, setProductsData] = useState(null);

  const loadData = async () => {
    const { data } = await getAxios().get('/market/list').then(response => response.data)
    setProductsData(data)
  }

  const useFilter = () => {
    return productsData.map(data => (...))
    //filters productsData
  };

  useEffect(()=>{
    loadData().then(()=>useFilter());
  },[])

Answer 1

Changing state asynchronous . So using state immediately after changing that may not be updated one.

You can use useEffect to call your function after state changed.

You can do this:

const [productsData, setProductsData] = useState(null);

const useFilter = () => {
  return productsData.map(data => (...))
  //filters productsData
};

useEffect(()=>{
  const loadData = async () => {
    const { data } = await getAxios().get('/market/list').then(response => response.data)
    setProductsData(data)
  }
  loadData()
},[])

useEffect(()=>{
  useFilter();
},[productsData])

Answer 2

Hello just by making a function async doesn't make it return a promise in order to use.then on function calls you must make sure they return promises

So one implementation you could do is:

    const [productsData, setProductsData] = useState(null);

  const loadData = () => {
    return getAxios().get('/market/list').then(response => response.data)
  }

  const useFilter = () => {
    return productsData.map(data => (...))
    //filters productsData
  };

  useEffect(()=>{
    loadData().then((data)=>{
    setProductsData(data);
    useFilter();
    }
   );
  },[])

In the above implementation I return the promise that axios returns you can also return your own promise by creating a promise using new Promise() constructor

Do let me know if you face any issues