Introduction to the library that changed how the web thinks about UI — and the most interviewed-for frontend skill today.
React introduced a then-radical idea: describe what the UI should look like for a given state, and let the library figure out how to make the actual DOM match that description, instead of manually wiring up every update by hand. That declarative, component-based model became the dominant way to build web UIs, and it's what the rest of the ecosystem — hooks, routing, state management, server rendering — has been built around ever since.
React interview questions test something narrower than 'can you build a UI.' They test whether you understand what's happening underneath — how reconciliation decides what actually changed, why a hook has to be called in the same order every render, when a re-render cascade is a real problem versus a non-issue — and whether you can judge which pattern actually fits a given situation instead of applying one by habit. That's why React prep skews toward internals and tradeoffs, not component syntax.
What you'll walk away knowing