| 1 | --- |
| 2 | title: Defer State Reads to Usage Point |
| 3 | impact: MEDIUM |
| 4 | impactDescription: avoids unnecessary subscriptions |
| 5 | tags: rerender, searchParams, localStorage, optimization |
| 6 | --- |
| 7 | |
| 8 | ## Defer State Reads to Usage Point |
| 9 | |
| 10 | Don't subscribe to dynamic state (searchParams, localStorage) if you only read it inside callbacks. |
| 11 | |
| 12 | **Incorrect (subscribes to all searchParams changes):** |
| 13 | |
| 14 | ```tsx |
| 15 | function ShareButton({ chatId }: { chatId: string }) { |
| 16 | const searchParams = useSearchParams() |
| 17 | |
| 18 | const handleShare = () => { |
| 19 | const ref = searchParams.get('ref') |
| 20 | shareChat(chatId, { ref }) |
| 21 | } |
| 22 | |
| 23 | return <button onClick={handleShare}>Share</button> |
| 24 | } |
| 25 | ``` |
| 26 | |
| 27 | **Correct (reads on demand, no subscription):** |
| 28 | |
| 29 | ```tsx |
| 30 | function ShareButton({ chatId }: { chatId: string }) { |
| 31 | const handleShare = () => { |
| 32 | const params = new URLSearchParams(window.location.search) |
| 33 | const ref = params.get('ref') |
| 34 | shareChat(chatId, { ref }) |
| 35 | } |
| 36 | |
| 37 | return <button onClick={handleShare}>Share</button> |
| 38 | } |
| 39 | ``` |
| 40 |