React JS Interview Questions and Answers
Prepare React JS interview questions with clear answers. Covers components, hooks, state management and real frontend scenarios for freshers.
React Basics
Q. What is React JS?
React JS is a JavaScript library used to build user interfaces using reusable components.
Q. What is a single page application?
A single page application loads a single HTML page and updates content dynamically without reloading the page.
Q. What is Virtual DOM?
Virtual DOM is a lightweight copy of the real DOM used by React to improve performance by updating only necessary parts.
Components
Q. What are functional components?
Functional components are simple JavaScript functions that return JSX to render UI.
Q. What are class components?
Class components are ES6 classes that extend React.Component and can manage state and lifecycle methods.
Q. What are props in React?
Props are inputs passed to components to display dynamic data.
Q. Why are components important in React?
Components make code reusable, maintainable, and easier to manage.
State and Hooks
Q. What is state in React?
State is used to store data that can change over time and affect how a component renders.
Q. What is useState hook?
useState is a hook used to add state to functional components.
Q. What is useEffect hook?
useEffect is used to handle side effects like API calls or updating the DOM.
Q. Why are hooks used in React?
Hooks allow using state and lifecycle features in functional components without using class components.
Routing and API
Q. What is React Router?
React Router is a library used for navigation between different pages in a React application.
Q. How do you fetch data in React?
Data can be fetched using fetch API or libraries like Axios inside useEffect.
Q. What is conditional rendering?
Conditional rendering allows displaying different UI based on conditions.
Performance and Best Practices
Q. What is React.memo?
React.memo is used to prevent unnecessary re-rendering of components.
Q. Why is key prop important in lists?
Key helps React identify elements and update them efficiently.
Q. How do you optimize a React app?
Optimization can be done by lazy loading, memoization, and reducing unnecessary renders.
Q. Why is project structure important?
A good structure improves maintainability and scalability of the application.
Tips to Crack Technical Interviews
Simple preparation tips to improve your performance across technical interviews for fresher roles.
Understand Core Concepts
Focus on components, props, state, and how React works internally.
Build Small Projects
Create apps like todo list or dashboard to understand real usage.
Practice Hooks
Hooks like useState and useEffect are commonly asked in interviews.
Explain Data Flow
Be ready to explain how data moves between components.
Focus on Practical Usage
Real project understanding matters more than theory.
Stay Updated
Keep learning updates and best practices in React ecosystem.
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