What is the virtual DOM and how does it help performance?
The virtual DOM is React's in-memory description of the UI. React compares new and previous descriptions and updates the real DOM only where they differ, a process called reconciliation. This makes updates efficient by minimizing DOM manipulation.
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More FAQs in React Performance and Optimization Interview Questions
Measure with the Profiler first, then optimize the real bottlenecks: useMemo for expensive computations, stabilize prop references with useCallback, virtualize long lists, code split routes, and debounce expensive inputs. Never optimize blindly.
useMemo memoizes a value, useCallback memoizes a function. useMemo is for expensive computations, useCallback is for stable function references passed to memoized children. Both prevent unnecessary work but serve different cases.
React.memo wraps a component so it re-renders only when its props change by reference. It is used with useCallback and useMemo to prevent re-renders when the parent re-renders but the props have not meaningfully changed.
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