Why do I get 'map is not a function' after fetching?
Because you assumed the data is an array when it is nested inside an object. Read the actual response shape, extract the array from the correct field, and only then call map on it.
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More FAQs in How to Fetch Data With useEffect in React the Right Way
Declare state for data, loading, and error. Fetch inside useEffect with an empty dependency array, handle the response shape, and guard against unmount with a cleanup flag or abort signal. Handle all three states: loading, error, and success.
Use a cleanup flag that tracks whether the component is still mounted, or use an AbortController to actually cancel the request. Only update state if the component is still mounted, so you avoid the warning about updating state on an unmounted component.
Because you included a state variable in the dependency array that you update inside the effect. Each update triggers another fetch. Use an empty array for one-time fetches, or include only values the fetch actually depends on, like an id.
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