Introduction
React remains the leading library for building modern user interfaces. With the release of React 19 and the widespread adoption of Server Components, interviewers have raised the bar, moving away from basic class components and focusing on hooks, concurrency, rendering states, and optimal performance patterns.
Below are 20 React quiz questions with clear answers and technical explanations. They cover essential concepts from state management and refs to newer hooks and React Server Components (RSC).
React Core Concepts & Hooks (1–10)
What is the primary purpose of the Virtual DOM?
Think of your answer, then reveal it to check.
Always mention performance hooks like `useMemo` and `useCallback` with caution. Emphasize that they have a memory overhead, and should only be applied when performance metrics justify it.
Advanced Rendering & React 19 features (11–20)
What are React Server Components (RSC)?
Think of your answer, then reveal it to check.
Do not use `"use client"` everywhere. Client components should be pushed down to the leaves of your component tree. Keep static layouts as Server Components for fast initial loads.