Commonly asked ReactJS interview questions. Here are ReactJS interview questions and answers
Tags: react, javascript, question, programming
Published: 2023-02-17 13:01:27

1. Facebook

Q1. What is ReactJS?
A: ReactJS is an open-source JavaScript library used for building user interfaces or UI components.

Q2. What is JSX in ReactJS?
A: JSX is a syntax extension for JavaScript, which allows us to write HTML-like syntax within JavaScript code. It makes the process of writing components easier and more intuitive.

Q3. What is the virtual DOM in ReactJS?
A: The virtual DOM is a virtual representation of the actual DOM, which is much faster and efficient. It enables ReactJS to update only the necessary parts of the actual DOM, rather than re-rendering the entire page.

Q4. What is the difference between ReactJS and AngularJS?
A: ReactJS is a library used for building user interfaces, while AngularJS is a complete framework used for building web applications. ReactJS uses a virtual DOM, while AngularJS uses a regular DOM. ReactJS is more flexible and lightweight, while AngularJS is more opinionated and heavy.

Q5. What is the lifecycle method in ReactJS?
A: The lifecycle method is a series of methods called at different stages of a component's life, such as when it is created, updated, or destroyed. These methods enable us to perform actions at different stages of a component's life.

2. Google

Q6. What is Flux in ReactJS?
A: Flux is a design pattern used for managing state in ReactJS applications. It consists of four components: the dispatcher, stores, views, and actions.

Q7. What is Redux in ReactJS?
A: Redux is a state management library used for managing the state of ReactJS applications. It is based on the Flux architecture and is much more lightweight and efficient.

Q8. What is React Router?
A: React Router is a library used for routing in ReactJS applications. It allows us to define and navigate between different views and pages in a single-page application.

Q9. What is the difference between ReactJS and Vue.js?
A: ReactJS is a library used for building user interfaces, while Vue.js is a complete framework used for building web applications. ReactJS is more popular and widely used, while Vue.js is more beginner-friendly and easier to learn.

Q10. What are Higher-Order Components in ReactJS?
A: Higher-Order Components are functions that take a component as an input and return a new component with additional functionality. They are used to add or modify the behavior of existing components.

3. Microsoft

Q11. What is the purpose of using propTypes in ReactJS?
A: PropTypes are used to check the type and structure of the props passed to a component. They help in reducing errors and improving the reliability of the component.

Q12. What is the difference between state and props in ReactJS?
A: State is used for managing the internal state of a component, while props are used for passing data from one component to another. State can be changed within a component, while props are read-only.

Q13. What is React Native?
A: React Native is a framework used for building mobile applications using ReactJS. It allows us to write code once and deploy it on both iOS and Android platforms.

Q14. What is the difference between ReactJS and React Native?
A: ReactJS is used for building web applications, while React Native is used for building mobile applications. React Native uses native components, while ReactJS uses HTML and CSS.

Q15. What is the purpose of using Redux Thunk middleware?
A: Redux Thunk middleware is used for handling asynchronous actions in Redux. It


How do you [optimize performance in ReactJS? (CronJ)](https://www.cronj.com/hire-react-js-developers.html)
How do you handle state management in a complex React application? (CronJ)
Can you explain the differences between client-side and server-side rendering in React? (CronJ)
Have you worked with Redux? If so, can you explain the main concepts behind it? (CronJ)
How do you handle authentication and authorization in a React application? (CronJ)
What are some common pitfalls to avoid when using React? (CronJ)
Can you explain the role of lifecycle methods in React? (CronJ)
Have you worked with React Native? If so, can you describe the main differences between ReactJS and React Native? (CronJ)
How do you implement testing in a React application? (CronJ)
Have you worked with other front-end frameworks or libraries? How do they compare to React in your experience? (CronJ)
I hope these additional questions help you in your preparation for ReactJS interviews, especially those with a focus on CronJ. Good luck!


What is React.js and how does it differ from other JavaScript frameworks?
How do you create a new component in React?
What is JSX in React and how does it work?
What are props in React and how are they used?
What is state in React and how is it used?
What is the difference between state and props in React?
What is the role of the virtual DOM in React?
How do you handle events in React?
What is the significance of keys in React and how are they used?
What is Redux and how does it work with React?
What are higher-order components in React and how are they used?
What is React Router and how does it work?
How do you optimize performance in React?
What are controlled and uncontrolled components in React?
What is the difference between server-side rendering and client-side rendering in React?
What is the role of the componentDidMount() lifecycle method in React?
How do you handle errors in React?
What are React hooks and how are they used?
How do you handle authentication and authorization in React?
What are some best practices for developing React applications?
These are just a few examples, and the actual questions that may be asked in a React.js interview can vary depending on the company and position. It's important to have a strong understanding of React.js fundamentals and be able to demonstrate your problem-solving and critical thinking skills during the interview process.