ReactJS Interview Questions and Answers

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 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.

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 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.

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 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 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.

Interview Preparation

ReactJS Interview Questions And Answers for Freshers and Experienced