react-expert
React gotchas and decision criteria covering stale closure bugs in useEffect, conditional rendering traps (falsy 0/empty string), state management selection (useState vs Context vs Zustand vs TanStack Query), and hooks rules. Use when writing React components, debugging re-renders, choosing state management, or encountering useEffect infinite loops.
What this skill does
> **AI-consumed reference.** Optimized for Claude to read during execution.
> Human-readable explanation: see [docs/architecture/HIERARCHICAL_PLANNING.md](../../../docs/architecture/HIERARCHICAL_PLANNING.md)
> or [docs/getting-started/](../../../docs/getting-started/) depending on topic.
# React Expert — Gotchas & Decisions
Use Context7 for full React docs.
## Key Decisions
```toon
decisions[5]{type,solution}:
Component-specific UI,useState
Shared between siblings,Lift to parent
Theme/auth/deep props,"Context + useMemo value + throw-if-outside-provider"
API/server data,TanStack Query or SWR
Complex global state,Zustand or Redux Toolkit
```
## Gotchas
- `{count && <X/>}` renders "0" when count=0 — use `{count > 0 && <X/>}`
- `{title && <X/>}` renders empty string — use `{title != null && title !== '' && <X/>}`
- Keys: unique IDs only, NEVER array indices (breaks on reorder/delete)
- useEffect with object/array deps → infinite loop. Destructure or useMemo the dep
- useEffect cleanup: return AbortController abort for async fetches
- useMemo/useCallback: only for expensive ops or stable refs to memoized children. Don't wrap everything
- Context: always `useMemo` the value object to prevent re-renders on every parent render
- Error boundaries: class component only (no hook equivalent yet). Wrap at route level
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