Split Combined Hook Computations
When a hook contains multiple independent tasks with different dependencies, split them into separate hooks. A combined hook reruns all tasks when any dependency changes, even if some tasks don't use the changed value.
Incorrect (changing sortOrder recomputes filtering):
const sortedProducts = useMemo(() => {
const filtered = products.filter((p) => p.category === category)
const sorted = filtered.toSorted((a, b) =>
sortOrder === "asc" ? a.price - b.price : b.price - a.price
)
return sorted
}, [products, category, sortOrder])Correct (filtering only recomputes when products or category change):
const filteredProducts = useMemo(
() => products.filter((p) => p.category === category),
[products, category]
)
const sortedProducts = useMemo(
() =>
filteredProducts.toSorted((a, b) =>
sortOrder === "asc" ? a.price - b.price : b.price - a.price
),
[filteredProducts, sortOrder]
)This pattern also applies to useEffect when combining unrelated side effects:
Incorrect (both effects run when either dependency changes):
useEffect(() => {
analytics.trackPageView(pathname)
document.title = `${pageTitle} | My App`
}, [pathname, pageTitle])Correct (effects run independently):
useEffect(() => {
analytics.trackPageView(pathname)
}, [pathname])
useEffect(() => {
document.title = `${pageTitle} | My App`
}, [pageTitle])Note: If your project has React Compiler enabled, it automatically optimizes dependency tracking and may handle some of these cases for you.