React

React interviews reward engineers who can trace data from user action to pixels. Strong answers name who owns each piece of state, what triggers a render, where synchronization belongs, and how the tree stays accessible and testable.

The curriculum spans components and JSX, hooks, reconciliation, component design patterns, forms, server and client data fetching, testing, and performance. Questions rarely stay on one API — interviewers connect hooks to list keys, controlled inputs to validation, or cache invalidation to optimistic UI.

On interviews, explain the concept with a concrete example and name the behavior interviewers probe.

Common pitfalls include hiding data flow, over-splitting components, and putting side effects in render.

The trade-off is often clarity versus reuse or explicit props versus convenience.

Checklist:

• Name the state owner before describing UI.
• Explain render triggers and batching.
• Keep render pure; reserve effects for external sync.
• Test behavior users and assistive tech can reach.