React Interview Questions & Answers
Prepare for React technical interviews with 100 curated questions and answers — from fundamentals to Tech Lead. Hooks, rendering, performance, and modern React patterns. Each question includes a short interview answer, detailed explanation, examples, tips, and common mistakes.
React interview topics
Jump into a category — each bank is independent and interview-focused.
Components
8 React questions
JSX
6 React questions
Props
6 React questions
State
7 React questions
Hooks
8 React questions
useEffect
7 React questions
useMemo
5 React questions
useCallback
5 React questions
Context
6 React questions
Rendering
7 React questions
Reconciliation
6 React questions
Performance
7 React questions
State Management
7 React questions
Server Components
6 React questions
Architecture
5 React questions
Testing
4 React questions
All React interview questions
Components interview questions
View categoryWhat is a React component?
freshFunction vs class components today?
freshWhat does it mean for a render to be pure?
freshControlled vs uncontrolled components?
freshWhen should you split a component?
freshWhat are fragments and why use them?
freshHow do error boundaries work?
freshDesign a reusable Modal component API.
freshJSX interview questions
View categoryProps interview questions
View categoryState interview questions
View categoryWhat is useState and when do you use it?
juniorWhy can setState appear async / batched?
juniorWhen do you lift state up?
junioruseState vs useReducer?
juniorStoring derived data in state — why is it a smell?
juniorHow do you update objects/arrays in state immutably?
juniorDesign state for a multi-step wizard form.
juniorHooks interview questions
View categoryWhat are the Rules of Hooks?
juniorWhat is a custom hook?
junioruseRef vs useState — when each?
juniorWhat does useId solve?
junioruseTransition vs useDeferredValue?
juniorWhat is useImperativeHandle for?
juniorHow do you test a custom hook?
juniorLead: how do you govern hooks usage across a large React codebase?
junioruseEffect interview questions
View categoryWhat is useEffect for?
juniorWhy does an effect run twice in React Strict Mode (dev)??
juniorHow do you correctly depend on props/state in effects?
juniorFetching in useEffect — modern guidance?
juniorWhen is useLayoutEffect preferred?
juniorEffect cleanup examples?
midAnti-pattern: chaining many effects to mirror state. What instead?
miduseMemo interview questions
View categoryuseCallback interview questions
View categoryContext interview questions
View categoryRendering interview questions
View categoryReconciliation interview questions
View categoryWhat is reconciliation?
seniorWhy do keys matter for list reconciliation?
seniorWhat happens when a component type changes at the same position?
seniorHow does React treat DOM attributes during updates?
seniorExplain bailing out of rendering with memo.
seniorDebug: input loses focus when typing in a list item.
seniorPerformance interview questions
View categoryHow do you approach React performance work?
seniorWhat does React.lazy + Suspense do for bundles?
seniorWindowing/virtualization — when?
seniorHow can Context hurt performance and how to fix?
seniorstartTransition for expensive filtered lists?
seniorImages and React perf?
seniorLead: set performance budgets for a React SPA.
seniorState Management interview questions
View categoryLocal state vs global state — how do you choose?
seniorWhat problem do Redux/Zustand/Jotai solve?
seniorServer state vs client state?
seniorHow does React Query change architecture?
seniorImmutable updates in stores — why?
seniorNormalize relational data in the client?
seniorWhen is Context enough without a store library?
senior