Question 170434 in Javascript Question posted in
A very good W3school tutorial can be found here.

Can’t read ‘map’ of undefined in React Mongo DB?

After executing my React code, I gotthe following error message in the browser console: "TypeError: Cannot read property ‘map’ of undefined". here is my code


const MyComponent = () => {
  const [data, setData] = useState([]);

  useEffect(() => {
    fetchData();
  }, []);

  const fetchData = async () => {
    const response = await fetch('https://api.example.com/data');
    const jsonData = await response.json();
    setData(jsonData);
  };

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

export default MyComponent;
Tags:

2

Answers


  1. 0

    I recommend that you use try…catch to handle possible errors in your request, so your app won’t break. Like this:

    const fetchData = async () => {
  try {
    const response = await fetch('https://api.example.com/data');
    const jsonData = await response.json();
    setData(jsonData);
  }
  catch (error) {
    // If the request returns an error...
    setData([]);
  }
}

    If the error persists, probably your request has no error but is not returning anything (undefined).

    Login or Signup to reply.
  2. 0 
    **You need to check first data should be defined when component renders **

 const MyComponent = () => {
    const [data, setData] = useState([]);

 useEffect(() => {
   fetchData();
 }, []);

 const fetchData = async () => {
  const response = await fetch('https://api.example.com/data');
  const jsonData = await response.json();
  setData(jsonData);
 };

 return (
    <div>
      {data && data.length?.map((item) => (
        <div key={item.id}>{item.name}</div>
      ))}
    </div>
  );
};

export default MyComponent;
    Login or Signup to reply.
Please signup or login to give your own answer.

Back To Top
Search