useMemo in React
From the React Hooks cheat sheet · Performance · verified Jul 2026
useMemo
Memoize expensive calculations
javascript
// Memoize expensive calculation
const expensiveValue = useMemo(() => {
return items.reduce((sum, item) => sum + item.value, 0)
}, [items]) // Recalculate when items change
// Memoize object/array to prevent re-renders
const options = useMemo(() => ({
color: 'blue',
size: 'large'
}), []) // Create once💡 Only use for expensive operations
⚡ React 19's compiler auto-memoizes - often unnecessary now
⚠️ Don't overuse - adds complexity
✅ Great for: sorting, filtering, calculations