Practice React hooks, component patterns, state management, and performance optimization with real interview scenarios
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Understand memoization, code splitting, and React profiler optimization techniques
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React Hooks (useState, useEffect, useCallback, useMemo)
Component lifecycle and rendering behavior
State management patterns (Redux, Context API)
Performance optimization techniques
Server-side rendering and Next.js
Testing with React Testing Library
A: useState triggers a re-render when the state changes, while useRef doesn't. useRef returns a mutable object that persists across renders without causing re-renders. Use useState for values that should update the UI, and useRef for values that don't affect rendering (like DOM references or timers).
A: The dependency array controls when useEffect runs. An empty array [] runs only on mount, no array runs on every render, and an array with values runs when those values change. Always include all values from the component scope that the effect uses to avoid stale closures.
A: React maintains a virtual representation of the DOM in memory. When state changes, React creates a new virtual DOM tree, compares it with the previous one (reconciliation), calculates the minimal set of changes needed, and updates only those parts of the real DOM. This makes updates more efficient.
A: useMemo memoizes the result of a computation, while useCallback memoizes the function itself. Use useMemo for expensive calculations and useCallback when passing functions to optimized child components to prevent unnecessary re-renders. Both accept dependency arrays.
Practice explaining your component design decisions and architecture choices
Be ready to discuss performance optimization strategies and when to apply them
Understand the differences between class components and functional components with hooks
Know how to debug React applications using React DevTools
Be familiar with common patterns like render props, HOCs, and compound components
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