react

Accessible React apps start with semantic HTML elements, use ARIA attributes only when native semantics fall short, manage focus programmatically for dynamic content, and ensure full keyboard navigation — interviewers test whether you treat a11y as an afterthought or a first-class concern.

Context provides data to any descendant component without passing props through every level — it solves prop drilling but is not state management, and context value changes re-render all consumers.

Controlled components use React state as the single source of truth for input values, while uncontrolled components let the DOM manage state and use refs to read values — each has tradeoffs for performance and complexity.

Hooks let functional components manage state (useState), run side effects (useEffect), access refs (useRef), and extract reusable logic into custom hooks — all following strict rules about call order.

UI component libraries fall into two categories — styled systems (MUI, Chakra) ship complete designs out of the box, while headless primitives (Radix, Headless UI) provide accessible behavior without opinions on styling, and shadcn/ui bridges the gap with copy-paste Radix+Tailwind components you own.

React Router provides client-side routing with nested routes and Outlet for layout composition, hooks for navigation (useNavigate, useParams), and data APIs (loaders/actions) for fetching data before rendering.