React TypeScript — Expert Patterns

<when_to_use>

• React 19 migration (ref as prop, useActionState, use())
• Generic components with type inference
• Server Components + Server Actions
• useEffect decisions (when to use, when NOT to)
• Derived state vs. effect-based state

NOT for: non-React TypeScript, vanilla JS React, styling/CSS, routing (use nextjs-app-router skill)

</when_to_use>

<effect_decision_tree>

Effects are an escape hatch. If no external system is involved, you don't need one.