React useEffect cleanup function not firing on component unmount with nested async calls
I'm refactoring my project and I'm dealing with I'm having trouble with the cleanup function in a `useEffect` hook not firing correctly when my component unmounts. I'm using React 17.0.2 and I have an async function inside my `useEffect` that makes an API call. The question arises when the component is unmounted before the async call completes; the cleanup function doesn't seem to execute, which leads to an attempt to set state on an unmounted component. Here's a simplified version of my code: ```javascript import React, { useEffect, useState } from 'react'; const MyComponent = () => { const [data, setData] = useState(null); const [loading, setLoading] = useState(true); useEffect(() => { let isMounted = true; setLoading(true); const fetchData = async () => { try { const response = await fetch('https://api.example.com/data'); const result = await response.json(); if (isMounted) { setData(result); } } catch (behavior) { console.behavior('Fetch behavior:', behavior); } finally { if (isMounted) { setLoading(false); } } }; fetchData(); return () => { isMounted = false; console.log('Cleanup function executed'); }; }, []); return <div>{loading ? 'Loading...' : JSON.stringify(data)}</div>; }; export default MyComponent; ``` Despite the `isMounted` flag, I still occasionally see a warning in the console stating "need to perform a React state update on an unmounted component." It seems that the cleanup function isn't executing when I navigate away from the page before the fetch completes. I've tried adding extra checks and logging to confirm whether the cleanup function is indeed running, but the warning continues. Am I missing something in my approach, or is there a better pattern to handle this scenario? This is happening in both development and production on CentOS. I appreciate any insights! I'm working in a Debian environment. Any ideas what could be causing this?