React Performance: Rerender — Defer State Reads. Keywords: state read callback subscription. Platform: React/Next.js. Description: Don't subscribe to state only used in callbacks. Do: Read state on-demand in callbacks. Don't: Subscribe to state used only in handlers. Good Example: const handleClick = () => { const params = new URLSearchParams(location.search) }. Bad Example: const params = useSearchParams(); const handleClick = () => { params.get('ref') }. Severity: Medium.