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Understand why React keys matter in list rendering. Learn how using array indexes as keys causes UI bugs like jumping input values, and why stable unique IDs are essential for proper reconciliation. Discover the difference between correct and incorrect key usage with practical examples.

Learn how React Reconciliation works - the smart update process that compares Virtual DOM trees using three key rules: different element types get replaced, same types get updated, and lists use keys for tracking. This efficient diffing algorithm reduces O(n³) complexity to O(n), updating only what actually changed in the real DOM.

Learn why React uses a Virtual DOM instead of direct DOM manipulation. Discover how this JavaScript object tree in memory optimizes performance by batching updates, reducing reflows and repaints, while providing a better developer experience through declarative UI patterns.

Learn about React component lifecycle - how components mount, update, and unmount - and understand the differences between class component lifecycle methods and function component Hooks.

Learn what JSX is, how it compiles from React 16 to React 17+, and master essential JSX syntax rules for writing React components.