React
Overview
Covers component architecture, performance optimization, state management, data fetching, and modern React 19+ APIs. Prioritizes React Compiler compatibility, Server Components, and elimination of data fetching waterfalls.
When to use: Building React applications, optimizing performance, choosing state management, implementing data fetching, reviewing component architecture.
When NOT to use: Non-React frameworks, purely server-side rendering without React, static sites without interactivity.
Quick Reference
| Pattern | API / Approach | Key Points |
|---|---|---|
| Data fetching | use(dataPromise) | Replaces useEffect+useState fetch pattern |
| Form handling | useActionState(action, init) | Built-in pending states and error handling |
| Optimistic UI | useOptimistic(state, updateFn) | Instant feedback while server processes |
| Non-urgent updates | useTransition() | Mark updates as interruptible |
| Effect events | useEffectEvent(fn) | Reactive values without re-triggering effects |
| Form pending status | useFormStatus() | Read parent form pending state from child component |
| Unique IDs | useId() | Hydration-safe IDs for accessibility |
| Server state | React Query / useSuspenseQuery | Caching, deduplication, background refetch |
| Client state (local) | useState / useRef | Single component or transient values |
| Client state (global) | Zustand / Context | Cross-component client-only state |
| Derived state | Compute during render | Never sync derived values with effects |
| Lazy initialization | useState(() => expensive()) | Avoid eager computation on every render |
| Component types | Page, Feature, UI | Route entry, business logic, reusable primitives |
| Memoization | Trust React Compiler first | Manual useMemo/useCallback only when needed |
| Ref as prop | ref prop on function components | No forwardRef needed in React 19 |
| Ref cleanup | Return function from ref callback | Cleanup runs on detach instead of null call |
| Code splitting | React.lazy() + Suspense | Lazy-load heavy components |
| Parallel fetches | Promise.all() | Eliminate sequential await waterfalls |
| Request dedup | React.cache() | Per-request server-side deduplication |
| Abort server work | cacheSignal() | Cancel expensive async work when client disconnects |
| Resource preloading | prefetchDNS, preconnect, preload, preinit | Optimize resource loading from components |
| State preservation | <Activity> | Hide UI while keeping state mounted |
Common Mistakes
| Mistake | Correct Pattern |
|---|---|
| Fetching data in useEffect with useState | Use the use() API or React Query for data fetching with built-in caching |
| Storing derived values in state and syncing with effects | Compute derived values during render; never use effects for state synchronization |
| Wrapping everything in useMemo and useCallback | Trust React Compiler first; only add manual memoization for expensive computations or memoized children |
Using array.sort() which mutates state | Use array.toSorted() for immutable sorting to avoid unexpected re-renders |
Using && for conditional rendering | Use ternary condition? <Component />: null to avoid rendering falsy values like 0 |
| Using Math.random() or Date for IDs | Use useId() for hydration-safe unique identifiers |
| Putting reactive values in effect deps to read latest value | Use useEffectEvent to access latest values without re-triggering effects |
| Creating object literals as effect dependencies | Hoist static objects outside the component or use primitive dependencies |
Using forwardRef in React 19 projects | Pass ref directly as a prop; forwardRef is deprecated in React 19 |
| Mutating props or state during render | Follow Rules of React for React Compiler compatibility: pure renders, no side effects |
Delegation
- Explore component architecture and identify performance bottlenecks: Use
Exploreagent to profile re-renders, analyze bundle size, and trace data fetching waterfalls - Implement React feature with proper patterns: Use
Taskagent to build components following Server Component, Suspense, and React 19 conventions - Design frontend architecture and state management strategy: Use
Planagent to structure component hierarchy, select state management, and plan data fetching approach
If theshadcn-uiskill is available, delegate component variant and theming questions to it. If thetailwindskill is available, delegate utility-first styling and design token questions to it. If thezustandskill is available, delegate global client state management questions to it.
References
- Component patterns, state management, and useEffect decisions
- Performance optimization: waterfalls, bundles, and re-renders
- Hooks, Server Actions, and React 19 APIs
- React Compiler patterns and re-render optimization
- Server-side rendering and React Server Components
- Anti-patterns and troubleshooting guide