If you last prepped for a React interview before 2025, there's a good chance your mental model is missing an entire layer of what gets asked now.
React 19 shipped Actions, useActionState, and ref as a regular prop. React 19.2 followed with useEffectEvent, the Activity component, and cacheSignal. And the React Compiler went stable in October 2025, which changes the default answer to "should I useMemo this?" from yes to "probably not, let the compiler handle it."
The fundamentals haven't gone anywhere. Props vs state, the key prop, reconciliation, the Rules of Hooks, these still get asked in nearly every interview regardless of seniority. But the questions that actually separate candidates who kept up from candidates repeating 2022 answers live in the React 19 specific territory: what problem does useEffectEvent actually solve, why is Activity different from conditionally unmounting a component, and can you explain Server Components vs traditional SSR in one clean sentence without getting flustered.
There's also a career-level layer that a lot of prep guides skip entirely: how do you test a component built around an Action, what ESLint setup does the Compiler actually need, and how would you explain the Client vs Server Component tradeoff to a teammate who hasn't caught up yet.
I put together 40 questions across five sections, fundamentals, hooks, React 19/19.2 specifics, performance and architecture, and testing/tooling, with a quick reference table so you can see all 40 at a glance before deciding where to spend your prep time. Full breakdown here: https://devencyclopedia.com/blog/react-interview-questions
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