This was the round that ended me the second time.
Start by clarifying the specific React internals area the interviewer wants to explore, then structure your answer around the core mechanism (e.g., Fiber reconciliation, hooks implementation, or scheduling) and explain how it enables React's declarative model. Use concrete examples from React's source code or your own debugging experience to demonstrate depth without getting lost in minutiae.
Pro tip: Admit when you don't know a specific internal detail, but pivot to how you would find the answer by reading React's source code or using React DevTools—this shows resourcefulness and honesty, which interviewers value over bluffing.
Ask the interviewer which specific internals they want to dive into (e.g., Fiber, hooks, reconciliation, scheduling) to focus your answer and avoid rambling.
Briefly describe the relevant React architecture (e.g., Fiber as a unit of work, double buffering, or the hooks linked list) to set context before diving into details.
Walk through the internal algorithm or data structures step-by-step, using precise terminology (e.g., work loop, effect list, lane model) and referencing how it solves a specific problem.
Explain how this internal behavior affects application code, performance, or debugging (e.g., why state updates are batched, or why hooks must be called unconditionally).
Discuss known trade-offs or edge cases in the implementation, and if unsure, state how you would investigate further using React's source or community resources.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.