{fullName}
\n}\n```\n\n**Correct: derive during render**\n\n```tsx\nfunction Form() {\n const [firstName, setFirstName] = useState('First')\n const [lastName, setLastName] = useState('Last')\n const fullName = firstName + ' ' + lastName\n\n return{fullName}
\n}\n```\n\nReference: [https://react.dev/learn/you-might-not-need-an-effect](https://react.dev/learn/you-might-not-need-an-effect)\n\n### 5.2 Defer State Reads to Usage Point\n\n**Impact: MEDIUM (avoids unnecessary subscriptions)**\n\nDon't subscribe to dynamic state (searchParams, localStorage) if you only read it inside callbacks.\n\n**Incorrect: subscribes to all searchParams changes**\n\n```tsx\nfunction ShareButton({ chatId }: { chatId: string }) {\n const searchParams = useSearchParams()\n\n const handleShare = () => {\n const ref = searchParams.get('ref')\n shareChat(chatId, { ref })\n }\n\n return \n}\n```\n\n**Correct: reads on demand, no subscription**\n\n```tsx\nfunction ShareButton({ chatId }: { chatId: string }) {\n const handleShare = () => {\n const params = new URLSearchParams(window.location.search)\n const ref = params.get('ref')\n shareChat(chatId, { ref })\n }\n\n return \n}\n```\n\n### 5.3 Do not wrap a simple expression with a primitive result type in useMemo\n\n**Impact: LOW-MEDIUM (wasted computation on every render)**\n\nWhen an expression is simple (few logical or arithmetical operators) and has a primitive result type (boolean, number, string), do not wrap it in `useMemo`.\n\nCalling `useMemo` and comparing hook dependencies may consume more resources than the expression itself.\n\n**Incorrect:**\n\n```tsx\nfunction Header({ user, notifications }: Props) {\n const isLoading = useMemo(() => {\n return user.isLoading || notifications.isLoading\n }, [user.isLoading, notifications.isLoading])\n\n if (isLoading) return{fullName}
\n}\n```\n\n**Correct: derive during render**\n\n```tsx\nfunction Form() {\n const [firstName, setFirstName] = useState('First')\n const [lastName, setLastName] = useState('Last')\n const fullName = firstName + ' ' + lastName\n\n return{fullName}
\n}\n```\n\nReference: [https://react.dev/learn/you-might-not-need-an-effect](https://react.dev/learn/you-might-not-need-an-effect)\n\n### 5.2 Defer State Reads to Usage Point\n\n**Impact: MEDIUM (avoids unnecessary subscriptions)**\n\nDon't subscribe to dynamic state (searchParams, localStorage) if you only read it inside callbacks.\n\n**Incorrect: subscribes to all searchParams changes**\n\n```tsx\nfunction ShareButton({ chatId }: { chatId: string }) {\n const searchParams = useSearchParams()\n\n const handleShare = () => {\n const ref = searchParams.get('ref')\n shareChat(chatId, { ref })\n }\n\n return \n}\n```\n\n**Correct: reads on demand, no subscription**\n\n```tsx\nfunction ShareButton({ chatId }: { chatId: string }) {\n const handleShare = () => {\n const params = new URLSearchParams(window.location.search)\n const ref = params.get('ref')\n shareChat(chatId, { ref })\n }\n\n return \n}\n```\n\n### 5.3 Do not wrap a simple expression with a primitive result type in useMemo\n\n**Impact: LOW-MEDIUM (wasted computation on every render)**\n\nWhen an expression is simple (few logical or arithmetical operators) and has a primitive result type (boolean, number, string), do not wrap it in `useMemo`.\n\nCalling `useMemo` and comparing hook dependencies may consume more resources than the expression itself.\n\n**Incorrect:**\n\n```tsx\nfunction Header({ user, notifications }: Props) {\n const isLoading = useMemo(() => {\n return user.isLoading || notifications.isLoading\n }, [user.isLoading, notifications.isLoading])\n\n if (isLoading) return{fullName}
\n}\n```\n\n**Correct: derive during render**\n\n```tsx\nfunction Form() {\n const [firstName, setFirstName] = useState('First')\n const [lastName, setLastName] = useState('Last')\n const fullName = firstName + ' ' + lastName\n\n return{fullName}
\n}\n```\n\nReference: [https://react.dev/learn/you-might-not-need-an-effect](https://react.dev/learn/you-might-not-need-an-effect)\n\n### 5.2 Defer State Reads to Usage Point\n\n**Impact: MEDIUM (avoids unnecessary subscriptions)**\n\nDon't subscribe to dynamic state (searchParams, localStorage) if you only read it inside callbacks.\n\n**Incorrect: subscribes to all searchParams changes**\n\n```tsx\nfunction ShareButton({ chatId }: { chatId: string }) {\n const searchParams = useSearchParams()\n\n const handleShare = () => {\n const ref = searchParams.get('ref')\n shareChat(chatId, { ref })\n }\n\n return \n}\n```\n\n**Correct: reads on demand, no subscription**\n\n```tsx\nfunction ShareButton({ chatId }: { chatId: string }) {\n const handleShare = () => {\n const params = new URLSearchParams(window.location.search)\n const ref = params.get('ref')\n shareChat(chatId, { ref })\n }\n\n return \n}\n```\n\n### 5.3 Do not wrap a simple expression with a primitive result type in useMemo\n\n**Impact: LOW-MEDIUM (wasted computation on every render)**\n\nWhen an expression is simple (few logical or arithmetical operators) and has a primitive result type (boolean, number, string), do not wrap it in `useMemo`.\n\nCalling `useMemo` and comparing hook dependencies may consume more resources than the expression itself.\n\n**Incorrect:**\n\n```tsx\nfunction Header({ user, notifications }: Props) {\n const isLoading = useMemo(() => {\n return user.isLoading || notifications.isLoading\n }, [user.isLoading, notifications.isLoading])\n\n if (isLoading) return{fullName}
\n}\n```\n\n**Correct: derive during render**\n\n```tsx\nfunction Form() {\n const [firstName, setFirstName] = useState('First')\n const [lastName, setLastName] = useState('Last')\n const fullName = firstName + ' ' + lastName\n\n return{fullName}
\n}\n```\n\nReference: [https://react.dev/learn/you-might-not-need-an-effect](https://react.dev/learn/you-might-not-need-an-effect)\n\n### 5.2 Defer State Reads to Usage Point\n\n**Impact: MEDIUM (avoids unnecessary subscriptions)**\n\nDon't subscribe to dynamic state (searchParams, localStorage) if you only read it inside callbacks.\n\n**Incorrect: subscribes to all searchParams changes**\n\n```tsx\nfunction ShareButton({ chatId }: { chatId: string }) {\n const searchParams = useSearchParams()\n\n const handleShare = () => {\n const ref = searchParams.get('ref')\n shareChat(chatId, { ref })\n }\n\n return \n}\n```\n\n**Correct: reads on demand, no subscription**\n\n```tsx\nfunction ShareButton({ chatId }: { chatId: string }) {\n const handleShare = () => {\n const params = new URLSearchParams(window.location.search)\n const ref = params.get('ref')\n shareChat(chatId, { ref })\n }\n\n return \n}\n```\n\n### 5.3 Do not wrap a simple expression with a primitive result type in useMemo\n\n**Impact: LOW-MEDIUM (wasted computation on every render)**\n\nWhen an expression is simple (few logical or arithmetical operators) and has a primitive result type (boolean, number, string), do not wrap it in `useMemo`.\n\nCalling `useMemo` and comparing hook dependencies may consume more resources than the expression itself.\n\n**Incorrect:**\n\n```tsx\nfunction Header({ user, notifications }: Props) {\n const isLoading = useMemo(() => {\n return user.isLoading || notifications.isLoading\n }, [user.isLoading, notifications.isLoading])\n\n if (isLoading) return