If you’re preparing for a React.js technical interview, knowing the most frequently asked questions can give you a competitive edge. The guide below offers in-depth explanations and practical insights into the most important topics interviewers love to ask.
1. What are the limitations of React in building large-scale applications?
React is powerful, but it’s not perfect. While it’s great for building dynamic user interfaces, large-scale applications introduce unique challenges.
a. SEO struggles and SSR dependency
React apps, when rendered purely on the client side, often face SEO challenges. Since the HTML is not fully rendered until JavaScript runs, search engine crawlers might miss out on important content. This is why Server-Side Rendering (SSR) frameworks like Next.js are often used to ensure better SEO performance.
b. Boilerplate chaos
React does not come with built-in routing, state management, or data fetching capabilities. This means developers must rely on third-party libraries such as React Router, Redux, or SWR, resulting in boilerplate-heavy codebases that can become difficult to maintain.
c. Overhead with state management
Managing complex states across many components can quickly become difficult. Redux and other state management libraries help but introduce complexity and boilerplate code.
2. How does React manage the Virtual DOM, and what are the benefits?
React’s Virtual DOM is a key performance booster.
a. What is the Virtual DOM?
The Virtual DOM is a lightweight JavaScript representation of the actual DOM. React uses it to figure out the minimal number of changes needed to update the real DOM efficiently.
b. The diffing algorithm
React compares the new Virtual DOM with the previous version using a diffing algorithm. Only the nodes that actually changed are updated in the real DOM.
c. Speed and performance wins
This approach drastically improves performance, especially in applications with many DOM updates. It ensures smoother user interactions and animations.
3. Can React Hooks fully replace Redux for state management?
Hooks provide a more modular and concise way to manage state, but they can’t always replace Redux.
a. Hooks vs. Redux
Hooks like useState, useReducer, and useContext offer local and basic global state management. For smaller applications or less complex state requirements, Hooks are enough.
b. Context API limitations
React Context is not designed to be a state management solution for large-scale applications. Any change in context will cause all consuming components to re-render.
c. When Redux still makes sense
Redux provides middleware support, time-travel debugging, and predictable state management, which is useful in large apps with complex flows.
4. What are the best practices for managing state in large React applications?
a. Global vs. local state
Use local state for UI-related logic and global state only when absolutely necessary (e.g., user authentication, theme settings).
b. Third-party libraries
Consider libraries like Zustand, Recoil, or Jotai which offer less boilerplate and better performance for specific use cases compared to Redux.
c. Component structure
Keep components small and focused. Lift state up only when multiple components need to share it.
5. How would you optimize performance in a React app with large component trees?
Read this full detailed article – Click here
6. Explain React’s Strict Mode and its impact on development
StrictMode is a tool for highlighting potential problems in an application.
a. What it does
It activates additional checks and warnings, such as identifying unsafe lifecycle methods, legacy API usage, and accidental side effects.
b. Double rendering in dev mode
StrictMode double-invokes some functions in development mode to detect unexpected side effects.
7. How can you prevent unnecessary re-renders in React functional components?
a. React.memo
Wrap functional components with React.memo to prevent re-renders when props haven’t changed.
b. useCallback
Memoize functions using useCallback so that they don’t get re-created on every render.
c. Dependency arrays
Ensure accurate and minimal dependency arrays in useEffect, useMemo, and useCallback to avoid unnecessary work.
8. Describe the key differences between functional and class components in React
a. Simpler syntax
Functional components are easier to read and write. They are just JavaScript functions.
b. Hooks
Hooks like useState and useEffect enable functional components to manage state and side effects without needing a class.
c. Lifecycle methods
Class components use componentDidMount, componentDidUpdate, and componentWillUnmount. Functional components achieve the same with useEffect.
9. What is the significance of the React Fiber architecture?
React Fiber is the underlying engine that powers React.
a. Concurrency
Fiber enables React to pause and resume work, making rendering more responsive and smooth.
b. Prioritization
It can assign priorities to tasks and discard low-priority work if more important updates come in.
c. Improved reconciliation
Fiber allows React to break down rendering work into units, improving performance and responsiveness.
10. How does React handle side effects, and how can you manage them effectively?
a. useEffect
useEffect allows you to perform side effects like API calls, subscriptions, or manual DOM manipulation in functional components.
b. Cleanup function
Return a cleanup function inside useEffect to handle things like clearing timers or unsubscribing from services.
c. Alternative tools
For advanced needs like data fetching and caching, use libraries like React Query, SWR, or Axios with custom hooks.
For more such Questions, stay tuned!
