rerender derived state

title: Subscribe to Derived State impact: MEDIUM impactDescription: reduces re-render frequency tags: rerender, derived-state, media-query, optimization

Subscribe to Derived State

Subscribe to derived boolean state instead of continuous values to reduce re-render frequency.

Incorrect (re-renders on every pixel change):

function Sidebar() {
  const width = useWindowWidth()  // updates continuously
  const isMobile = width < 768
  return <nav className={isMobile ? 'mobile' : 'desktop'}>
}

Correct (re-renders only when boolean changes):

function Sidebar() {
  const isMobile = useMediaQuery('(max-width: 767px)')
  return <nav className={isMobile ? 'mobile' : 'desktop'}>
}

本文档为站内渲染。原始文件本地路径：saas/source/knowledge-world/Knowledge-World-项目-Practice-Claude-Skills-vercel-react-best--2f741f.md（仅本地保留，不入库不部署）