React Interview 2

💻 JavaScript — Core Concepts & Output-Based Questions

• var vs let vs const (with scope)
• Hoisting & how it works internally
• Temporal Dead Zone (TDZ)
• == vs ===
• Closures & lexical scope retention
• Callback hell → Promises → async/await
• Event loop & handling async tasks
• Sync vs async execution
• Output-based puzzles on closures, TDZ, shadowing, hoisting

• Form handling & efficient state management
• API integration + loading/error handling
• Why fetch calls are placed inside useEffect
• Hooks: useState, useEffect, useMemo, useCallback
• Context API vs Redux
• Prop drilling & solutions
• React state management strategies
• React Router: relative vs absolute paths
• Virtual DOM & reconciliation
• Performance optimisations
• Reducing a 5-second homepage load
• Importance of keys in lists
• React lifecycle
• Avoiding unnecessary re-renders
• Handling API errors & retry logic

🧩 Git — Practical, Production-Level Scenarios

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another interview

1️⃣ How does the Virtual DOM actually improve performance?
2️⃣ When should you use useCallback and useMemo?
3️⃣ Can you explain prop drilling with a real example?
4️⃣ What’s the difference between controlled vs uncontrolled components?
5️⃣ How does React.memo() prevent unnecessary renders?
6️⃣ What happens when you call setState internally?
7️⃣ How do you optimize React components in large projects?

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𝗗𝗮𝘆 𝟭-𝟮: 𝗝𝗮𝘃𝗮𝗦𝗰𝗿𝗶𝗽𝘁 (𝟱 𝗰𝗼𝗻𝗰𝗲𝗽𝘁𝘀)   • Closures (stale closures in React)   • Promises & async (race conditions, error handling)   • Event loop (execution order)   • This keyword (binding rules)   • Debouncing/Throttling (implement from scratch)

𝗗𝗮𝘆 𝟯-𝟰: 𝗥𝗲𝗮𝗰𝘁 (𝟱 𝗽𝗮𝘁𝘁𝗲𝗿𝗻𝘀)   • When components re-render (4 triggers)   • useEffect (dependencies, cleanup, common bugs)   • useState (functional updates, stale closures)   • useCallback vs useMemo (when to use)   • Custom hooks (useDebounce, useFetch)

𝗗𝗮𝘆 𝟱-𝟲: 𝗠𝗮𝗰𝗵𝗶𝗻𝗲 𝗖𝗼𝗱𝗶𝗻𝗴 (𝟱 𝗰𝗼𝗺𝗽𝗼𝗻𝗲𝗻𝘁𝘀) Build each in 45 minutes:   • Todo list (CRUD + localStorage)   • Autocomplete (debouncing + keyboard nav)   • Modal (accessibility + focus trap)   • Tabs (state management + keyboard)   • Infinite scroll (Intersection Observer)

𝗗𝗮𝘆 𝟳 — 𝗠𝗼𝗰𝗸 𝗶𝗻𝘁𝗲𝗿𝘃𝗶𝗲𝘄 • Morning — review weak spots • Afternoon — timed build (45 min) • Evening — mental prep & rest

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Next.js

✅ I realized that if you know React well, Next.js is not a big jump.
All you need is clarity on these core concepts:
⚙️ SSR (Server-Side Rendering) vs CSR (Client-Side Rendering) vs Server Side Rendering When do you prefer CSR over SSR

File-based Routing
📦 API Routes in Next.js
🧠 getServerSideProps, getStaticProps, and getStaticPaths
⚡ App Router (app directory) and server components

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