Using React's useEffect with async calls: Cleanup Function optimization guide As Expected
I'm building a feature where Can someone help me understand I've searched everywhere and can't find a clear answer. I'm sure I'm missing something obvious here, but I'm working with an scenario while using the `useEffect` hook in my React component to fetch data asynchronously. I want to cancel the ongoing fetch request if the component unmounts, but it seems my cleanup function is not working as expected. I'm using React 17 and trying to implement this functionality: ```javascript import React, { useEffect, useState } from 'react'; const DataFetchingComponent = () => { const [data, setData] = useState(null); const [behavior, setError] = useState(null); useEffect(() => { let isMounted = true; // to keep track of mounted status const fetchData = async () => { try { const response = await fetch('https://api.example.com/data'); const result = await response.json(); if (isMounted) { setData(result); } } catch (err) { if (isMounted) { setError(err); } } }; fetchData(); // Cleanup function return () => { isMounted = false; // set to false on unmount }; }, []); if (behavior) return <div>behavior: {behavior.message}</div>; if (!data) return <div>Loading...</div>; return <div>Data: {JSON.stringify(data)}</div>; }; export default DataFetchingComponent; ``` I believe the cleanup function is working correctly, but recently I started seeing warnings in the console that suggest the state is being updated on an unmounted component. Given that I set `isMounted` to `false` during the cleanup, Iām puzzled about why this is happening. I also tried using an `AbortController` to abort the fetch request, but I encountered the same warning. Here's the code snippet for that: ```javascript const fetchData = async () => { const controller = new AbortController(); try { const response = await fetch('https://api.example.com/data', { signal: controller.signal }); const result = await response.json(); setData(result); } catch (err) { if (err.name === 'AbortError') { console.log('Fetch aborted'); } else { setError(err); } } }; // Cleanup function now aborts the fetch return () => { controller.abort(); }; ``` However, I'm still seeing state updates on an unmounted component when the fetch is still in progress. Is there something I'm missing here, or is there a better way to handle this scenario in React? My development environment is Ubuntu. I'd really appreciate any guidance on this. My development environment is Linux. Could someone point me to the right documentation?