version: "1.0.1" name: rerender-memo description: Extract expensive work into memoized components with React.memo. Apply when components perform expensive computations that can be skipped when props haven't changed.
Extract to Memoized Components
Extract expensive work into memoized components to enable early returns before computation.
Incorrect (computes avatar even when loading):
tsx
function Profile({ user, loading }: Props) {
const avatar = useMemo(() => {
const id = computeAvatarId(user)
return <Avatar id={id} />
}, [user])
if (loading) return <Skeleton />
return <div>{avatar}</div>
}
Correct (skips computation when loading):
tsx
const UserAvatar = memo(function UserAvatar({ user }: { user: User }) {
const id = useMemo(() => computeAvatarId(user), [user])
return <Avatar id={id} />
})
function Profile({ user, loading }: Props) {
if (loading) return <Skeleton />
return (
<div>
<UserAvatar user={user} />
</div>
)
}
Note: If your project has React Compiler enabled, manual memoization with memo() and useMemo() is not necessary. The compiler automatically optimizes re-renders.