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Cannot read properties of undefined (reading 'map')

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Mr not.Ok answered on July 15, 2021 Popularity 9/10 Helpfulness 1/10

answer Cannot read properties of undefined (reading 'map')

related TypeError: Cannot read property 'map' of undefined

related Cannot read properties of undefined (reading 'map') - useQuery

Cannot read properties of undefined (reading 'map')

Comment

-1

In plain terms, the error occurs when you try to map over an undefined value, 
such as an array that has not been initialized or has not yet received data.

Popularity 9/10 Helpfulness 1/10 Language javascript

Source: Grepper

Tags: javascript properties undefined

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Contributed on Dec 08 2023

Mr not.Ok

0 Answers Avg Quality 2/10

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TypeError: Cannot read property 'map' of undefined

Comment

function MyComponent() {
  const [data, setData] = useState([]);
  const [loading, setLoading] = useState(false);

  useEffect(() => {
    setLoading(true);
    fetch('/api/data')
      .then((res) => res.json())
      .then((data) => {
        setData(data);
      })
      .catch((err) => {
        console.log(err);
      })
      .finally(() => {
        setLoading(false);
      });
  }, []);

  if (loading) {
    return <p>Data is loading...</p>;
  }

  return (
    <ul>
      {data.map((item) => (
        <li key={item.id}>{item.name}</li>
      ))}
    </ul>
  );
}

Popularity 10/10 Helpfulness 3/10 Language javascript

Source: typeofnan.dev

Tags: javascript j

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Contributed on Jul 15 2021

Average Ant

0 Answers Avg Quality 2/10

Cannot read properties of undefined (reading 'map') - useQuery

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// NOTE - This solution works when your working with REACT-QUERY
const fetchPlanets = async (page) => {
  // const [_key, page] = queryKey;
  const response = await fetch(`https://swapi.dev/api/planets/?page=${page}`);
  if (!response.ok) {
    throw new Error("Network response was not ok");
  }
  return response.json();
};

const Planents = () => {
  const [page, setPage] = useState(2);
  //this point did the magic, and enable the [page-state] 
  //to be seen at the fetch function
  const { data, status } = useQuery(["planets", page], () =>
    fetchPlanets(page)
  );
  console.log(data);
  return (
    <div>
      <h2>Planets</h2>
      {status === "pending" && <div>Loading Data</div>}
      {status === "error" && <div>Error fetching data</div>}
      {status === "success" && (
        <div>
          {data.results.map((planet) => {
            return <SinglePlanet key={planet.name} planet={planet} />;
          })}
        </div>
      )}
    </div>
  );
};

Popularity 10/10 Helpfulness 1/10 Language javascript

Source: stackoverflow.com

Tags: javascript j

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Contributed on Feb 18 2022

Godwin_NJ

0 Answers Avg Quality 2/10

Cannot read properties of undefined (reading 'map')

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Cannot read properties of undefined (reading 'map')

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TypeError: Cannot read property 'map' of undefined

Cannot read properties of undefined (reading 'map') - useQuery

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