react-useeffect
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
useSyncExternalStorewhen possible)
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