React interview questions and answers

Streaming can send the shell quickly so TTFB and first paint improve even if a slow widget is still pending.

React matches by key, so state lives with the identity, not the position.

I keep a small set of variants, sizes, and an asChild or polymorphic pattern so consumers do not fork the CSS.

useMemo caches an expensive calculated value between renders.

React.memo wraps a component so it skips re-render when props are shallow-equal.

Component composition, context for sparse global values, or lightweight stores for frequent updates.