React

React: Topics Not to Miss

Check off each topic before your interview.

Fundamentals

• What React is (UI library, component-based, declarative)
• JSX — expressions, fragments, keys
• Components: function components (class awareness only)
• Props — read-only, drilling, children prop
• Conditional rendering (&&, ternary)
• Lists and key prop — why not index for dynamic lists

State & Hooks

• useState — batching, functional updates
• useEffect — deps array, cleanup, when NOT to use
• useRef — DOM access, mutable values without re-render
• useContext — avoid prop drilling
• useMemo / useCallback — when they help vs hurt
• useReducer — complex state logic
• Rules of Hooks

Rendering

• Virtual DOM concept (reconciliation)
• What triggers re-render
• Controlled vs uncontrolled inputs
• Lifting state up
• Composition vs inheritance

Data Fetching

• useEffect + fetch pattern
• Loading, error, empty states
• Race conditions (abort controller)
• React Query / SWR awareness (optional bonus)

Routing & Structure

• React Router basics (Route, Link, useParams, useNavigate)
• Folder structure for medium apps
• Custom hooks for reusable logic

Forms

• Controlled components
• Form libraries awareness (React Hook Form)
• Validation approach

Performance

• Unnecessary re-renders
• React.memo, useMemo, useCallback
• Code splitting / lazy + Suspense
• List virtualization (awareness)

Testing & Tooling (awareness)

• Vite vs CRA
• ESLint + React hooks plugin
• Basic component test concept (React Testing Library)

React 18+ (bonus)

• Concurrent features awareness
• useTransition, useDeferredValue (high level)
• Strict Mode double-invoke in dev

Self-test: Can you build a searchable product list with loading/error states using hooks in 45 minutes? Can you explain why your useEffect dependency array is correct?