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Top ReactJS Interview Questions and Answers

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ReactJS interview questions are frequently asked in Java interviews at top tech companies. ReactJS is a powerful, free, open-source JavaScript library that helps to build scalable front-end applications and user interfaces. ReactJS has become extremely popular in present times, offering developers heightened flexibility in library usage while building front-end components for websites and applications.

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In this article, we’ll cover some popular ReactJS interview questions and answers to help you prepare and get ready for your upcoming technical interview.

Here’s what we’ll discuss in this article:

  • Most Popular ReactJS Interview Questions and Answers
  • FAQs on ReactJS Interview Questions

Most Popular ReactJs Interview Questions and Answers

This section will look at some popular ReactJS interview questions, mostly asked at Java developer and SQL developer interviews.

Q1. What are some advantages of using ReactJS?

This is a popular ReactJs interview question asked in Java interviews. ReactJs offers a host of advantages to front-end developers. They include:

  • React is extremely easy to use when compared to other frameworks. Even with limited knowledge of JavaScript, you can start building applications using ReactJS. 
  • The ReactJs framework is highly SEO friendly, offering front-end developers to make tweaks to improve website performance by optimizing the application/web page. 
  • React allows for reusable components as it incorporates a component-based architecture model. Components are nothing but bits of code that can be reused, and React allows developers to re-use and modify code whenever and wherever necessary with ease.
  • React uses a virtual DOM, improving the efficiency of applications created. 
  • React offers a vast list of libraries and tools, allowing developers impressive depth and flexibility.

Q2. What is JSX in React?

JSX is short for JavaScript XML and allows developers to write HTML code inside JavaScript and subsequently associate it with the DOM without using functions such as createElement() and appendChild().

Q3. What do you understand about Virtual DOM?

The Virtual DOM in ReactJs is when a virtual representation of the real DOM is placed inside the memory. The virtual DOM is then synced with the real or actual DOM by the ReactDOM library. 

Q4. What are the different lifecycle phases in ReactJS?

This is yet another frequently asked ReactJS interview question. Lifecycle phases in ReactJS allow developers to alter the phase of a given lifecycle. The different lifecycle phases that components or blocks of code go through include:

  • Mounting
  • Updating
  • Unmounting

Q5. What are the different Lifecycle methods in the Mounting lifecycle phase?

The lifecycle methods under the Mounting lifecycle phase are:

  • ComponentWillMount
  • Render
  • ComponentDidMount

Q6. What are the lifecycle methods in the Updating phase?

The methods under the Updating lifecycle phase are:

  • ComponentWillReceiveProps
  • shouldcomponentUpdate
  • componentWillUpdate
  • Render
  • componentDidUpdate

Q7. What are the lifecycle methods in the Unmounting phase?

There is just one lifecycle method associated with the Unmounting Phase — componentWIllUnmount

Q8. Can browsers directly read JSX?

This is one of the popular ReactJS interview questions asked. The answer is no; web browsers aren’t built so that they can read JSX directly. That’s fundamental because browsers are built only to read regular JavaScript objects. JSX isn’t a regular object and cannot be read by browsers. For browsers to read JSX, the given file needs to be converted into a regular JavaScript object.

Q9. What are the steps involved in creating the React app?

The steps involved in creating the React app include:

  • Install the NodeJS file on your computer because we need npm to install the React library. Npm is the node package manager that contains many JavaScript libraries, including React.
  • Install the create-react-app package
  • Install a text editor, and you’re ready to go.

Q10. What do you understand about an event in React?

An event is an action performed by the user or computer. Any action that involves pressing a key, mouse clicks, or typing out sentences, classify as events. React events are in camelCase, unlike lowercase in HTML.

Q11. What do you understand about a component in React?

A component in react is a block of code that serves as a building block of the React application. Components are part of the UI and split user interfaces into multiple reusable parts, processing each part individually.

Q12. What are the two types of components in React?

Knowing the answer to this ReactJS interview question is essential. The two types of components in React are - Functional Components and Class Components.

Q13. What do you understand about Synthetic events in React?

Synthetic events in React are events that combine native events of different browsers into a single API, thereby ensuring consistency.

Q14. How do you achieve the traversal of lists in React?

This is a common ReactJS interview question asked at Java interviews. In React, the traversal of lists can be accomplished through the map() function.

Q15. Why do we need to use keys in React lists?

Keys are extremely helpful in identifying lists and changes that have been made to items in lists. They also signify which components in the library need to be re-rendered based on the corresponding updates and prevent other items from unnecessarily being re-rendered.

We’ve compiled a list of the most commonly asked ReactJS interview questions and answers in this article. We hope this helps you prepare for your technical interview.

FAQs on ReactJs Interview Questions

Q1. What is ReactJs, and what is it used for?

ReactJs is a popular open-source and flexible JavaScript library that allows developers to build scalable user interfaces and front-end applications.

Q2. When can you expect to be asked ReactJS interview questions?

You can expect to be asked ReactJS interview questions in Java developer interviews, as React is a JavaScript library. 

Q3. Do you need to have in-depth knowledge of ReactJS while appearing for Java technical interviews?

Knowing your way around how React works is sufficient. The good thing about React is that even with fundamental JavaScript knowledge, you can go about building applications.

Q4. What are some concepts around which React interview questions are asked in technical interviews?

Some common concepts around which you’re asked React interview questions at tech interviews are lifecycle methods, events in React, lists, forms, functions, components, and commands used in React.

Q5. What is the use of the Arrow function in React?

The Arrow function helps to write short-form versions of functions in React, saving time and assisting developers in avoiding errors.

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