react-useeffect
This Claude Code skill provides React useEffect best practices from official documentation, teaching developers when Effects are genuinely needed versus when better alternatives exist. Use this when writing or reviewing useEffect and useState hooks to learn proper patterns for data fetching, state synchronization, derived values, and external system integration, along with guidance on superior alternatives like useMemo, event handlers, and the key prop.
git clone --depth 1 https://github.com/softaworks/agent-toolkit /tmp/react-useeffect && cp -r /tmp/react-useeffect/dist/plugins/react-useeffect/skills/react-useeffect ~/.claude/skills/react-useeffectSKILL.md
# 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)
- **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
1. **Transforming data for rendering** - Calculate at top level, re-runs automatically
2. **Handling user events** - Use event handlers, you know exactly what happened
3. **Deriving state** - Just compute it: `const fullName = firstName + ' ' + lastName`
4. **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](./anti-patterns.md) - Common mistakes with fixes
- [Better Alternatives](./alternatives.md) - useMemo, key prop, lifting state, useSyncExternalStoreAdd a skill to the project with validation and README generation
Sync root README.md with current skills inventory from skills/ directory
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