main_frontend/.agents/skills/react-best-practices/references/rules/rerender-simple-expression-in-memo.md

title, impact, impactDescription, tags

title	impact	impactDescription	tags
Do not wrap a simple expression with a primitive result type in useMemo	LOW-MEDIUM	wasted computation on every render	rerender, useMemo, optimization

Do not wrap a simple expression with a primitive result type in useMemo

When an expression is simple (few logical or arithmetical operators) and has a primitive result type (boolean, number, string), do not wrap it in useMemo. Calling useMemo and comparing hook dependencies may consume more resources than the expression itself.

Incorrect:

function Header({ user, notifications }: Props) {
  const isLoading = useMemo(() => {
    return user.isLoading || notifications.isLoading
  }, [user.isLoading, notifications.isLoading])

  if (isLoading) return <Skeleton />
  // return some markup
}

Correct:

function Header({ user, notifications }: Props) {
  const isLoading = user.isLoading || notifications.isLoading

  if (isLoading) return <Skeleton />
  // return some markup
}