how can I use async data from node api?

Question

I'm fetching data from node.js. So it's kinda late to get data... I guess that's why my console says 'null' all the time :/ I tried several way to fix it, but it didn't help at all.

I did use UseState but it ended up saying 'null' data. My page kept saying

TypeError: Cannot read property 'map' of null

here's my react code:


const Start = () => {
  const [isLoading, setIsLoading] = useState(false);

  const dataList = null;

  useEffect(() => {
    const getData = async () => {
      setIsLoading(true);
      await axios
        .post('/api/getData')
        .then((res) => {
          console.log(res.data.result);
          // 👆 at this point, this console.log says what I exactly want.
          return (dataList = res.data.result);
        })
        .catch((err) => console.log(err));
      setIsLoading(false);
    };

    getData();
  }, []);

  if (isLoading) return <div>...Loading...</div>;

  return (
    <div>
            
      {dataList.map((item, idx) => (
        <p>{item[0].dataName}</p>
      ))}
          
    </div>
  );
};

What should I do to use my data which was fetched from node.js? the data is long, large JSON.

Antonio Erdeljac · Accepted Answer · 2021-01-25 22:47:51Z

To properly use React, you should keep data inside the state, so React's virtual DOM can properly render items according to that data (for your case).

Also, no need to chain .then whilst using await.

On another note, it is weird that you are using axios.post instead of axios.get for fetching the data, just a piece of friendly advice.

The reason why your const dataList = null never gets updated is because you are initializing it inside the render function, meaning every time the state gets updated (setIsLoading) your dataList gets reinitialized to null

const Start = () => {
  const [isLoading, setIsLoading] = useState(false);
  const [dataList, setDataList] = useState([]);

  useEffect(() => {
    const getData = async () => {
      setIsLoading(true);

      const response = await axios.post('/api/getData');

      setIsLoading(false);
      setDataList(response.data.result);
    };

    getData();
  }, []);

  if (isLoading) {
    return <div>...Loading...</div>;
  }

  return (
    <div>
      {dataList.map((item, idx) => (
        <p>{item[0].dataName}</p>
      ))}
    </div>
  );
};

thanks for pointing my silly mistakes out! but it still got same problems :(

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