---

name: React Performance description: Optimization strategies for React applications (Client & Server). metadata: labels: [react, performance, optimization, nextjs] triggers: files: ['/*.tsx', '/*.jsx'] keywords: [waterfall, bundle, lazy, suspense, dynamic]

React Performance

Priority: P0 (CRITICAL)

Strategies to minimize waterfalls, bundle size, and render cost.

Elimination of Waterfalls (P0)

• Parallel Data: Use Promise.all for independent fetches. Avoid sequential await.
• Preload: Start fetches before render (in event handlers or route loaders).
• Suspense: Use Suspense boundaries to stream partial content.

Bundle Optimization (P0)

• No Barrel Files: Import directly import { Btn } from './Btn' vs import { Btn } from './components'.
• Lazy Load: React.lazy / next/dynamic for heavy components (Charts, Modals).
• Defer: Load 3rd-party scripts (Analytics) after hydration.

Rendering & Re-renders (P1)

• Isolation: Move state down. Isolate heavy UI updates.
• Context Splitting: Split Context into StateContext (Data) and DispatchContext (Actions) to prevent consumers from re-rendering just because they need a setter.
• Stability: Use useMemo for passing objects/arrays to children to preserve referential equality checks (React.memo).
• Virtualization: react-window for lists > 50 items.
• Content Visibility: content-visibility: auto for off-screen CSS content.
• Static Hoisting: Extract static objects/JSX outside component scope.
• Transitions: startTransition for non-urgent UI updates.

Parallelization (P1)

• Web Workers: Move heavy computation (Encryption, Image processing, Large Data Sorting) off the main thread using Comlink or Worker.

Server Performance (RSC) (P1)

• Caching: React.cache for per-request deduplication.
• Serialization: Minimize props passing to Client Components (only IDs/primitives).

Anti-Patterns

• No export *: Breaks tree-shaking.
• No Sequential Await: Causes waterfalls.
• No Inline Objects: style={{}} breaks strict equality checks (if memoized).
• No Heavy Libs: Avoid moment/lodash (use dayjs/radash).

Code

Copy// Parallel Fetching (Good)
const [user, posts] = await Promise.all([getUser(), getPosts()]);

// Bundle Optimized Import (Good)
import { Button } from './components/Button'; // Not from './components'

// Static Hoist (Good)
const STATIC_CONFIG = { theme: 'dark' };
function Component() {
  return <div config={STATIC_CONFIG} />;
}