# 309 Rerender Simple Expression In Memo 5bdcf2d1

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

- Skill: `tools-only/309-rerender-simple-expression-in-memo-5bdcf2d1` (Agent Skill, multi-file: 3 files)
- Install (CLI): `npx skillmds@latest add tools-only/309-rerender-simple-expression-in-memo-5bdcf2d1`
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- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: tools-only (https://skillmd.com/u/tools-only)
- Updated: 2026-09-22
- Page: https://skillmd.com/skills/tools-only/309-rerender-simple-expression-in-memo-5bdcf2d1

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## 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:**

```tsx
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:**

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

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