react-useeffect

name	react-useeffect
description	React useEffect best practices from official docs. Use when writing/reviewing useEffect, useState for derived values, data fetching, or state synchronization. Teaches when NOT to use Effect and better alternatives.

You Might Not Need an Effect

Effects are an escape hatch from React. They let you synchronize with external systems. If there is no external system involved, you shouldn't need an Effect.

Quick Reference

Situation	DON'T	DO
Derived state from props/state	useState + useEffect	Calculate during render
Expensive calculations	useEffect to cache	useMemo
Reset state on prop change	useEffect with setState	key prop
User event responses	useEffect watching state	Event handler directly
Notify parent of changes	useEffect calling onChange	Call in event handler
Fetch data	useEffect without cleanup	useEffect with cleanup OR framework

When You DO Need Effects

• Synchronizing with external systems (non-React widgets, browser APIs)
• Subscriptions to external stores (use useSyncExternalStore when possible)
• that runs because component displayed