Fetch and setInterval react hooks problem

Question

I recently used hooks with React to fetch data from server but i'm facing a problem with hooks. The code seems correct but it look like the useEffect isn't called at first time but 3 seconds after with the setInterval. I have blank table for 3 seconds before it appear. I want to directly show the data and call it 3 seconds later.

What is the correct way to use it?

const [datas, setDatas] = useState([] as any);

useEffect(() => {
  const id = setInterval(() => {
    const fetchData = async () => {
      try {
        const res = await fetch(URL);
        const json = await res.json();
        setDatas(jsonData(json));
      } catch (error) {
        console.log(error);
      }
    };
    fetchData();
  }, TIME)

  return () => clearInterval(id);
}, [])

Answer 1

You need to invoke fetchData once initially outside the interval. Define fetchData outside the interval.

useEffect(() => {
  // (1) define within effect callback scope
  const fetchData = async () => {
    try {
      const res = await fetch(URL);
      const json = await res.json();
      setDatas(jsonData(json));
    } catch (error) {
      console.log(error);
    }
  };
    
  const id = setInterval(() => {
    fetchData(); // <-- (3) invoke in interval callback
  }, TIME);

  fetchData(); // <-- (2) invoke on mount

  return () => clearInterval(id);
}, [])