About react-useeffect
A React guidance skill for developers deciding when to use Effects. It explains alternatives for derived state, events, and calculations, while covering synchronization with external systems.
Key features
- 01Guidance on when Effects are needed
- 02Alternatives for derived state
- 03Event-handler recommendations
- 04useMemo for expensive calculations
- 05Cleanup guidance for data fetching
Use cases
- 01Review a component that uses Effects for derived data
- 02Choose an approach for responding to user actions
- 03Plan synchronization with an external system
Install
Copy the command and run it in a terminal.
$
npx skills add https:/After installing, type/react-useeffectin Claude Code to confirm it loaded.
Bundled files
References and scripts installed along with SKILL.md.
alternatives.mdanti-patterns.mdREADME.mdDetails
From the project READMEYou 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) - Analytics/logging that runs because component displayed
- Data fetching with proper cleanup (or use framework's built-in mechanism)
When You DON'T Need Effects
- Transforming data for rendering - Calculate at top level, re-runs automatically
- Handling user events - Use event handlers, you know exactly what happened
- Deriving state - Just compute it:
const fullName = firstName + ' ' + lastName - Chaining state updates - Calculate all next state in the event handler
Decision Tree
Need to respond to something?
├── User interaction (click, submit, drag)?
│ └── Use EVENT HANDLER
├── Component appeared on screen?
│ └── Use EFFECT (external sync, analytics)
├── Props/state changed and need derived value?
│ └── CALCULATE DURING RENDER
│ └── Expensive? Use useMemo
└── Need to reset state when prop changes?
└── Use KEY PROP on component
Detailed Guidance
- Anti-Patterns - Common mistakes with fixes
- Better Alternatives - useMemo, key prop, lifting state, useSyncExternalStore
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