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Mirrors .cursor and .codex structure with Claude model assignments: - haiku for lighter tasks (translator, browser-check, profiler) - sonnet for standard tasks (code-quality, plan-implementer, etc.) Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
30 lines
728 B
Markdown
30 lines
728 B
Markdown
---
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title: Subscribe to Derived State
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impact: MEDIUM
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impactDescription: reduces re-render frequency
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tags: rerender, derived-state, media-query, optimization
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---
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## Subscribe to Derived State
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Subscribe to derived boolean state instead of continuous values to reduce re-render frequency.
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**Incorrect (re-renders on every pixel change):**
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```tsx
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function Sidebar() {
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const width = useWindowWidth() // updates continuously
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const isMobile = width < 768
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return <nav className={isMobile ? 'mobile' : 'desktop'} />
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}
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```
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**Correct (re-renders only when boolean changes):**
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```tsx
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function Sidebar() {
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const isMobile = useMediaQuery('(max-width: 767px)')
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return <nav className={isMobile ? 'mobile' : 'desktop'} />
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}
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```
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