React Developer interview questions

A senior React developer should master key JavaScript concepts such as closures, promises, async/await, ES6+ features like destructuring, spread/rest operators, arrow functions, prototypal inheritance, and functional programming patterns. In-depth understanding of these concepts ensures optimal React code structure and maintainability.

React component lifecycle consists of mounting, updating, and unmounting phases. Each phase contains methods such as componentDidMount, shouldComponentUpdate, componentDidUpdate, and componentWillUnmount that are used for tasks like API calls, performance optimization, and cleanup processes in class components. In functional components, useEffect hooks are utilized to achieve similar side effects.

Large scale React applications utilize local state (useState/useReducer), context API for lightweight state sharing, and external libraries such as Redux, MobX, and Zustand for complex state management. Advanced patterns may also include leveraging React Query or Apollo Client for remote state management, depending on the application's architecture.

Performance optimization techniques include using React.memo to memoize components, useCallback and useMemo hooks to prevent unnecessary re-creations, implementing shouldComponentUpdate or React.PureComponent for class components, and proper state structuring to avoid prop drilling and deep nested updates.

Controlled components rely on React state to manage their input data, ensuring data consistency and validation. Uncontrolled components depend on direct DOM access via refs. Senior developers use controlled components for predictable form behavior and consider uncontrolled when performance or direct DOM manipulation is required.

Best practices include separating presentational and container components, using folder-based modular structures, implementing reusable and atomic components, following clear naming conventions, and utilizing barrel files for exports. Proper architectural patterns such as feature-based or domain-driven design foster scalability and maintainability.

Side effects in React are primarily handled using useEffect, useLayoutEffect hooks in functional components, and lifecycle methods in class components. For complex scenarios, middleware like Redux Thunk, Redux Saga, or use of custom hooks are employed to manage asynchronous actions and side effects.

Redux offers predictable state management, robust debugging tools, and efficient state sharing across the application. Limitations include increased boilerplate, potential over-architecture for small projects, and possible challenges in handling asynchronous actions unless middleware is used.

Considerations include ensuring browser compatibility using tools like Babel, leveraging ES6+ syntax for cleaner code (such as destructuring, arrow functions, modules), and maintaining consistent coding standards across the team to ensure all features are correctly transpiled and supported.

Improper state management can result in unnecessary re-renders, memory leaks, laggy user interfaces, and difficulty in maintaining component logic. Efficient state structuring, minimizing prop drilling, and using appropriate state management techniques are essential to achieving optimal performance and maintainability in React applications.