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.agents/skills/vercel-react-best-practices/rules/rerender-defer-reads.md

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+---
+title: Defer State Reads to Usage Point
+impact: MEDIUM
+impactDescription: avoids unnecessary subscriptions
+tags: rerender, searchParams, localStorage, optimization
+---
+
+## Defer State Reads to Usage Point
+
+Don't subscribe to dynamic state (searchParams, localStorage) if you only read it inside callbacks.
+
+**Incorrect (subscribes to all searchParams changes):**
+
+```tsx
+function ShareButton({ chatId }: { chatId: string }) {
+  const searchParams = useSearchParams();
+
+  const handleShare = () => {
+    const ref = searchParams.get('ref');
+    shareChat(chatId, { ref });
+  };
+
+  return <button onClick={handleShare}>Share</button>;
+}
+```
+
+**Correct (reads on demand, no subscription):**
+
+```tsx
+function ShareButton({ chatId }: { chatId: string }) {
+  const handleShare = () => {
+    const params = new URLSearchParams(window.location.search);
+    const ref = params.get('ref');
+    shareChat(chatId, { ref });
+  };
+
+  return <button onClick={handleShare}>Share</button>;
+}
+```