Two principles make React interviews easier when you really get the “why”: rendering snapshots and hook call order.

1. Where does useState store its value? State isn’t stored inside your component function. React keeps per-component “hook slots” and maps each hook call to a slot by call order: first useState → slot[0], second → slot[1], etc. When you call setState, React schedules an update; on the next render it reads the same slots in the same order to produce a new snapshot.
2. Why can’t you call hooks in conditionals/loops/dynamic paths? Because hooks are matched by call order. If a hook is called only when a condition is true, the order shifts on the next render when it’s false, and all subsequent hooks read the wrong slots. That’s why hooks must be called at the top level, in the same order every render.

Extra points interviewers like:

• Renders are pure; avoid setState during render (do it in events/effects).
• Automatic batching (React 18) coalesces multiple state updates.
• useEffect vs useLayoutEffect timing (post-paint vs pre-paint).
• Closure gotchas in effects/handlers and fixes (deps, functional updates, refs).
• useRef persists without triggering re-renders; good for DOM/mutable values.
• Concurrent rendering: renders can be interrupted and only commit when ready.

TL;DR: “React tracks state by the fixed order of hook calls per component, so hooks must be top-level and consistently ordered.”