👀 Views: 0 💬 Answers: 1 📅 Created: 2025-06-18

reactjs hooks performance javascript

I'm trying to debug I'm stuck on something that should probably be simple. I'm currently working on a React 18 application and trying to create a custom hook to fetch user data from an API. However, I'm working with performance optimization since the data fetch is being triggered unnecessarily on every render. I want to leverage `useMemo` to cache the fetched data, but I'm unsure how to implement this correctly without causing stale data issues. Here's what I have so far: ```javascript import { useState, useEffect, useMemo } from 'react'; const useFetchUsers = (url) => { const [users, setUsers] = useState([]); const [loading, setLoading] = useState(true); useEffect(() => { const fetchData = async () => { const response = await fetch(url); const result = await response.json(); setUsers(result); setLoading(false); }; fetchData(); }, [url]); return [users, loading]; }; const UsersList = ({ apiUrl }) => { const [users, loading] = useFetchUsers(apiUrl); const memoizedUsers = useMemo(() => users, [users]); if (loading) return <p>Loading...</p>; return ( <ul> {memoizedUsers.map((user) => ( <li key={user.id}>{user.name}</li> ))} </ul> ); }; ``` The `useEffect` is supposed to fetch the data only when the `url` changes, but I'm seeing that it still triggers on every render when the component re-renders. I have tried adding an empty dependency array, but that causes the data not to update when the `url` changes. The warning I get is `React Hook useEffect has a missing dependency: 'url'. Either include it or remove the dependency array`. It seems that `users` is being re-fetched even when it hasn't changed, which I need to understand. How can I cache the results properly and ensure they only fetch when the `url` changes? Any guidance on best practices here would be greatly appreciated! For context: I'm using Javascript on Windows. I'm coming from a different tech stack and learning Javascript.