👀 Views: 44 💬 Answers: 1 📅 Created: 2025-06-12

reactjs usememo performance javascript

I've hit a wall trying to I'm experiencing an issue where a component that uses `useMemo` is re-rendering more often than I expect, even though the dependencies haven't changed... I'm using React 18 and have the following code: ```javascript import React, { useMemo, useState } from 'react'; const MyComponent = () => { const [count, setCount] = useState(0); const [filter, setFilter] = useState(''); const filteredItems = useMemo(() => { console.log('Filtering items...'); return items.filter(item => item.includes(filter)); }, [filter]); return ( <div> <input type="text" value={filter} onChange={(e) => setFilter(e.target.value)} /> <button onClick={() => setCount(count + 1)}>Increment Count</button> <div>Count: {count}</div> <ul>{filteredItems.map(item => <li key={item}>{item}</li>)}</ul> </div> ); }; const items = ['apple', 'banana', 'orange', 'grape']; export default MyComponent; ``` I've noticed that every time I click the "Increment Count" button, the console logs "Filtering items...", indicating that the `useMemo` is recalculating even though the `filter` hasn't changed. I expected it to only recalculate when `filter` changes. My understanding was that `useMemo` should help optimize performance by memoizing the result based on the provided dependencies. I’ve tried separating the `setCount` and `setFilter` functions and ensuring they don’t affect each other. I also verified that `items` is not a dependency here, but it feels like there's something else triggering the re-render. What could be causing this behavior, and how can I prevent unnecessary recalculations? Any insights would be appreciated, thanks! Any feedback is welcome!