121. What is the primary benefit of React 19's Actions feature?
- a) Simplified data mutations with automatic pending states
- b) Replacement for useEffect
- c) Built-in API caching
- d) Automatic WebSocket integration
Answer: A - Actions handle async operations with integrated loading/error states.
122. How to integrate WebAssembly with React?
- a) wasm-pack + React hooks
- b) Emscripten-generated JS glue code
- c) Custom React reconciler
- d) Both A and B
Answer: D - WASM modules work like regular JS libraries with optimized performance.
123. What is Edge SSR's main advantage over traditional SSR?
- a) Lower latency via geographic distribution
- b) Smaller bundle sizes
- c) Automatic code splitting
- d) No client-side JavaScript needed
Answer: A - Edge networks reduce TTFB by executing near users.
124. How to use React 19's useOptimistic hook?
- a) Show temporary UI during async actions
- b) Replace Redux state management
- c) Prefetch components
- d) Optimize image loading
Answer: A - Provides instant UI feedback before server confirmation.
125. What is the purpose of React Compiler?
- a) Automatically memoize components/props
- b) Convert JSX to vanilla JS
- c) Replace Babel
- d) Enable Python in React
Answer: A - Analyzes code to apply optimizations traditionally done manually with useMemo/useCallback.
126. How to implement a WebWorker with React?
- a) comlink library + useEffect
- b) Next.js API routes
- c) React's built-in Worker API
- d) Edge Functions
Answer: A - Comlink simplifies RPC-style communication with workers.
127. What is React Server Components' limitation?
- a) No hooks/state/effects
- b) Larger bundle size
- c) Slower hydration
- d) Requires GraphQL
Answer: A - RSCs are purely for rendering and data fetching.
128. How does React 19 improve hydration?
- a) Progressive enhancement
- b) Lazy element attachment
- c) No hydration needed
- d) Both A and B
Answer: D - Reduces jank by prioritizing visible content.
129. What is WASM's primary use case in React?
- a) CPU-intensive tasks (image/video processing)
- b) Replace React core
- c) State management
- d) CSS animations
Answer: A - Offloads heavy computations from main thread.
130. How to implement Edge SSR in Next.js?
- a) export const runtime = 'edge'
- b) Custom document component
- c) React Server Components
- d) All of the above
Answer: A - Next.js 13+ supports edge runtime per route.
131. What is React 19's Document Metadata feature?
- a) Built-in title/meta tag management
- b) Replace next/head
- c) Automatic SEO optimization
- d) Both A and B
Answer: D - Allows setting metadata anywhere in component tree.
132. How to optimize React for Core Web Vitals?
- a) Code splitting + lazy loading
- b) Image optimization
- c) Selective hydration
- d) All of the above
Answer: D - Targets LCP, FID, and CLS metrics.
133. What is the purpose of React's use hook?
- a) Consume promises/context in components
- b) Replace useState
- c) Experimental WASM integration
- d) All of the above
Answer: A - Simplifies working with async data (React Canary feature).
134. How does Edge SSR handle authentication?
- a) Middleware with cookies
- b) JWT in edge functions
- c) Both A and B
- d) No auth support
Answer: C - Requires stateless auth due to edge's distributed nature.
135. What is React 19's asset loading improvement?
- a) Automatic image/styling dependency tracking
- b) WASM bundle splitting
- c) Replace Webpack
- d) All of the above
Answer: A - Knows when assets are used/not used in components.
136. How to measure WebAssembly performance in React?
- a) Performance.measure() API
- b) React Profiler
- c) Custom benchmarking
- d) All of the above
Answer: D - Compare JS vs WASM execution times for specific tasks.
137. What is the limitation of Edge SSR?
- a) Smaller runtime API surface
- b) No Node.js modules
- c) Cold starts
- d) All of the above
Answer: D - Edge environments have compute/memory constraints.
138. How does React 19 optimize re-renders?
- a) Automatic memoization
- b) Compiler-generated optimization
- c) Both A and B
- d) No improvements
Answer: C - Reduces need for manual useMemo/useCallback.
139. What is the benefit of WASM threads in React?
- a) Parallel computation
- b) Shared memory
- c) Both A and B
- d) No React integration
Answer: C - Enables true multithreading for heavy tasks.
140. How to deploy Edge SSR on Vercel?
- a) Automatic with next.config.js
- b) Custom serverless function
- c) Edge middleware
- d) Both A and C
Answer: D - Next.js handles edge deployment configuration automatically.