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Cannot read properties of undefined (reading 'map')

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