In React.js interviews, candidates can expect questions covering a broad spectrum of topics relevant to front-end development using the React library. These inquiries often delve into understanding React component lifecycle methods, the management of state and props within components, and the concept of the virtual DOM, which React utilizes for efficient rendering. Interviewers may also probe candidates' knowledge of React Hooks, a feature introduced in React 16.8 for managing state and side effects in functional components. Additionally, questions may explore topics such as component composition techniques, client-side routing with libraries like React Router, and state management approaches using tools like Redux or the context API. Candidates should be prepared to discuss strategies for error handling, performance optimization, and testing methodologies specific to React applications. Overall, a comprehensive understanding of React principles, coupled with practical experience and the ability to articulate solutions effectively, is essential for navigating React.js interviews successfully.

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ReactJS Interview Questions And Answers for
Freshers and Experienced
POSTED ON FEBRUARY 25, 2022 BY GEEKSTER
ReactJS Interview Questions And Answers For Freshers:
Question 1. What is ReactJS?
Question 2. What is the difference between state and props?
Question 3. What is JSX?
Question 4. How can you include JavaScript in JSX?
Question 5. What is a stateless component?
ReactJS Interview Questions And Answers For Experienced:
Question 6. How are stateless components different from stateful components?
Question 7. What are some of the benefits of writing ReactJS applications with
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Question 7. What are some of the benefits of writing ReactJS applications with
ES6?
Question 8. What is the difference between a controlled and uncontrolled
component?
Question 9. How would you implement validation for form fields in ReactJS?
Question 10. How would you implement a file uploader in ReactJS?
Question 11. How do you set up a local development environment for ReactJS?
Question 12. Can you implement lazy loading in ReactJS?
Question 13. How would you implement a modal pop-up in ReactJS?
Question 14. How would you implement a loading indicator in ReactJS?
Question 15. How can you implement a persistent shopping cart in ReactJS?
Question 16. How would you implement client-side routing with ReactJS?
Question 17. How would you implement infinite scrolling in ReactJS?
Question 18. What are fragments and why might they be useful in ReactJS?
Question 19. How would you implement authentication in ReactJS with local
storage?
Question 20. How would you handle Ajax requests in ReactJS?
Conclusion
Related Articles
ReactJS is a JavaScript library for building user interfaces. It lets you create reusable
components so that your code is easy to read and maintain. ReactJS is popular
among web developers because it makes creating complex user interfaces simpler. If
you’re looking for a job as a ReactJS developer, you’ll need to know how to answer
interview questions about this library. Here are the top 20 commonly asked ReactJS
interview questions and answers for freshers and experienced.
ReactJS Interview Questions And Answers For
Freshers:
Question 1. What is ReactJS?
Answer – ReactJS is an open-source JavaScript library that allows developers to
build user interfaces. It lets you create reusable components, which will help you
write easy-to-read code that’s also easier to maintain.
Question 2. What is the difference between state and props?
Answer – State and props are two types of data that can be passed to React

3. Answer – State and props are two types of data that can be passed to React
components:
State: This represents the data for one particular instance of a component. It’s good
for small pieces of information that change often, such as whether or not something
is checked. It’s private to each instance of the component.
Props: This represents data that is passed to a component, but it shouldn’t change. It
goes through one level only and cannot be changed except by its parent.
State vs. Props
Question 3. What is JSX?
Answer – JSX stands for JavaScript XML, and it allows developers to write
components in an HTML-like syntax. This means that you can include HTML tags in
JavaScript, which makes code easier to read.
Question 4. How can you include JavaScript in JSX?
Answer – You place JavaScript inside of an opening and closing <script> tag and
construct your code like normal.
Question 5. What is a stateless component?
Answer – A stateless component is a component that does not keep track of any
data, and therefore cannot change it. Stateless components are also known as

4. data, and therefore cannot change it. Stateless components are also known as
presentational components.
ReactJS Interview Questions And Answers For
Experienced:
Question 6. How are stateless components different from stateful
components?
Answer – Stateless components are simpler than stateful ones because they don’t
keep track of any data. They just return what you give them, which makes it easier to
create reusable components. Stateless components also have an advantage over
the more traditional approach of keeping all of your data in the DOM. This is because
it’s possible to update your components even if your data comes from an external
source.
Question 7. What are some of the benefits of writing ReactJS
applications with ES6?
Answer – Since JavaScript is evolving so quickly, developers can stay ahead of the
curve by using Babel for transpiling their ES6 code into a format that browsers can
understand. Babel also has a wide range of plugins available for it, which lets
developers write code in newer ECMAScript specifications that they might not have
been able to use otherwise.
Question 8. What is the difference between a controlled and
uncontrolled component?
Answer – An uncontrolled component uses the default DOM behavior of updating,
whereas a controlled component does not. Controlled components also use refs to
request changes from HTML.

5. Question 9. How would you implement validation for form fields in
ReactJS?
Answer – The best way to do this depends on what you’re trying to validate. If you
just need to check for a value, React provides a built-in way of doing so with the
required function. You can also use refs to add an onBlur event in your input fields
and check whether a certain value has been entered when they lose focus.
Question 10. How would you implement a file uploader in ReactJS?
Answer – To make a form element that’s capable of uploading files, you can use the
<input type=”file” /> tag. You can then use a ref to store a handle to this element and
either add an event listener when it gains focus or changes its state when it loses
focus. A controlled component is also necessary if you need to have the possibility of
an upload failing.
Question 11. How do you set up a local development environment for
ReactJS?
Answer – You can use both Docker and create-react-app to help with setting up
your local environment, but it’s much easier to just use create-react-app because it
does all of the work for you.
Question 12. Can you implement lazy loading in ReactJS?
Answer – React doesn’t currently offer any kind of built-in functionality that lets you
defer the loading of components. However, you can use async components to break
up your code and delay unpacking it until a certain point in time.
Question 13. How would you implement a modal pop-up in ReactJS?
Answer – You can make a Modal component that displays whatever content you
want, and then add an event listener to call a handler when it has been shown. This
handler should also make the original component visible again.
Question 14. How would you implement a loading indicator in

6. Question 14. How would you implement a loading indicator in
ReactJS?
Answer – The easiest way to do this is by using either an animated gif or an
animated spinning icon. Then, use the componentDidMount() function for your main
App component to set up an interval that hides and shows it. You can also show a
different spinner when there is an error.
Question 15. How can you implement a persistent shopping cart in
ReactJS?
Answer – The easiest way to store a shopping cart is by using local storage, which
lets you access it on multiple pages. You also need to save the items as they are
added and remove them as they are removed from the list.
Question 16. How would you implement client-side routing with
ReactJS?
Answer – You can use either React Router or react-router-dom for this task. The
main difference between the two is that react-router-dom uses the HTML5 history
API, whereas React Router uses fake routing.
Question 17. How would you implement infinite scrolling in ReactJS?
Answer – The easiest way to do this is by creating a loading indicator of some kind,
so the user knows it’s happening. Then, load more data on scroll with an interval that
checks how far down the page the user has scrolled.
Question 18. What are fragments and why might they be useful in
ReactJS?
Answer – Fragments let you group multiple components together and return them as
a single unit from a function. They’re useful when you want to return multiple
elements at once and scope variables inside of the return statement. This lets you
avoid using ternary operators or if statements to determine where variables should
be used.
Question 19. How would you implement authentication in ReactJS
with local storage?
Answer – You can use JSON Web Tokens to store the data required for authentication
on the client side. Then, once logged in, you can ensure they remain logged in by
adding them as an item to local storage. When they log out, simply delete their token

7. adding them as an item to local storage. When they log out, simply delete their token
from local storage and it doesn’t matter if they refresh the page or not.
Question 20. How would you handle Ajax requests in ReactJS?
Answer – The easiest way to do this is by using either Axios, Query AJAX or
Superagent. You can then add an event listener that contains any code you need to
run before the request begins, and another event listener to run after the request
finishes.
Conclusion
Each time developers face an interviewer, they wish they had known some basic
questions that the interviewer might ask. In this article, we have covered the top 20
ReactJS interview questions and answers that will make your job easy. Also, you can
practice with these ReactJS interview questions and answers with your friends and
colleagues to prepare for any upcoming interview.
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