Fetch and setInterval react hooks problem

user_7973127 0
Viewed 2079

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);
  }, [])
react-hooks reactjs setinterval fetch
2 Answers

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);
}, [])
user_86908570

With React Hooks:

  const [seconds, setSeconds] = useState(0)

  const interval = useRef(null)

  useEffect(() => { if (seconds === 60) stopCounter() }, [seconds])

  const startCounter = () => interval.current = setInterval(() => {
    setSeconds(prevState => prevState + 1)
  }, 1000)

  const stopCounter = () => clearInterval(interval.current)
user_132106970
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