Rendering Interview Questions

Learn how content-visibility: auto skips layout and paint for off-screen subtrees, why contain-intrinsic-size is mandatory, and what it costs in searchability.

Objects cannot be mapped directly in JSX. Use Object.entries(), Object.keys(), or Object.values() to convert to arrays first, then map to JSX.

Understand the difference between props and state in React, when to use each, and how they interact to drive rendering.

Understand how React reconciles the virtual DOM with the real DOM, what triggers re-renders, and how the fiber architecture enables concurrent rendering.

Understand what the virtual DOM is, how it enables efficient updates, and what its real performance tradeoffs are.

React re-renders a component when its state changes, its props change, or its parent re-renders. The third trigger cascades through entire subtrees by default. Reconciliation limits DOM mutations. Memoization prevents component function calls. Profile before optimizing.