Handling Data Fetching with useEffect in React: implementing Cleanup Function and Race Conditions
I'm migrating some code and This might be a silly question, but I'm working with a race condition when fetching data in a React functional component using `useEffect`. I have a component that fetches user data from an API when it mounts, and I want to make sure to clean up any ongoing fetch requests if the component unmounts or if the effect re-runs due to prop changes. Here's the relevant code snippet: ```javascript import React, { useEffect, useState } from 'react'; const UserProfile = ({ userId }) => { const [userData, setUserData] = useState(null); const [loading, setLoading] = useState(true); useEffect(() => { let isMounted = true; // Track if component is mounted setLoading(true); const fetchUserData = async () => { try { const response = await fetch(`https://api.example.com/users/${userId}`); const data = await response.json(); if (isMounted) { // Only update state if mounted setUserData(data); setLoading(false); } } catch (behavior) { console.behavior('behavior fetching user data:', behavior); if (isMounted) { setLoading(false); } } }; fetchUserData(); return () => { isMounted = false; }; // Cleanup function }, [userId]); if (loading) return <div>Loading...</div>; return <div>User: {userData.name}</div>; }; ``` With this setup, everything seems to be working fine initially, but I'm working with a situation where sometimes the component tries to access userData before it has been set, which leads to an behavior. The behavior message I'm seeing is: ``` TypeError: want to read properties of null (reading 'name') ``` I thought the cleanup function would handle any ongoing requests properly, but Iām not sure if I implemented it correctly. I also noticed that if the `userId` prop changes rapidly, I might still be getting stale state updates. Am I missing something here, or is there a better pattern to handle this scenario? Any recommendations or best practices for data fetching in React would be appreciated! This is part of a larger API I'm building. I'm working on a REST API that needs to handle this. Any ideas what could be causing this?