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1. What is the Virtual DOM, and how does it improve performance?
The Virtual DOM is a lightweight JavaScript copy of the real browser DOM. React updates this virtual version first, then efficiently applies only the necessary changes to the actual DOM, reducing costly browser operations.

2. How does React’s diffing algorithm work?
React’s O(n) diffing algorithm assumes that elements of different types create different trees and that the key prop helps identify stable elements across renders, making updates faster.

3. What are the three phases of React’s reconciliation process?

Render Phase: React builds a new Virtual DOM.

Diffing Phase: It compares the new and old Virtual DOMs.

Commit Phase: Only the required changes are applied to the real DOM.

4. What is React.PureComponent used for?
React.PureComponent performs a shallow comparison of props and state. If nothing has changed, React skips re-rendering the component and its children, improving performance.

5. How does Reselect optimize Redux selectors?
Reselect creates memoized selectors that store their previous results. They only recompute if their input data changes, preventing unnecessary recalculations on every state update.

6. Why is mutating props considered an anti-pattern?
Mutating props changes the data but not the reference, which breaks shallow comparisons used in React.PureComponent and React.memo. As a result, React may not detect updates, causing rendering issues.

7. What does the useDeferredValue hook do?
useDeferredValue helps prevent UI lag by letting immediate updates (like typing) happen first and deferring heavier tasks to a later render cycle—unlike debouncing, it doesn’t delay work but reschedules it efficiently.

8. What is a flamegraph, and how is it useful?
A flamegraph shows component rendering performance. Yellow means longer render times, blue-green means faster renders, and gray indicates no render. It helps identify slow components during interactions.

9. What is tree shaking, and how can it be enabled in Webpack?
Tree shaking removes unused code from your final bundle. To enable it, set Webpack mode to 'production' and add "sideEffects": false in package.json to safely eliminate unused imports.

10. How do dynamic imports and route-based code splitting improve load time?
They load code only when needed, splitting your app into smaller bundles instead of one large file. This reduces the initial download size and speeds up the first page load.

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