Common React interview questions and sample answers

By Indeed Editorial Team

Published 19 May 2022

The Indeed Editorial Team comprises a diverse and talented team of writers, researchers and subject matter experts equipped with Indeed's data and insights to deliver useful tips to help guide your career journey.

React, or ReactJS, is a popular Javascript library that developers use to build front-end developments such as website applications. React is often used by front-end developers in JavaScript to create scalable web applications quickly and easily. If you're thinking of applying for a job in this industry, it can be useful to know about React and review some common interview questions. In this article, we discuss some of the most common React interview questions and provide sample answers to help you prepare for a technical interview.

What is React?

React is an open-source library of Javascript components that allows developers to create front-end applications, user interfaces and web applications that are scalable. Developers can pull specific components from the library and implement them into their code for extra functionality. React is a JavaScript library, which means that the code found in React uses the JavaScript coding language.

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Common React interview questions and sample answers

Although no two job interviews are alike, there are usually several common themes or topics that React interview questions address. To help you prepare for a technical interview, here are some sample questions that recruiters commonly ask and how to answer them:

1. What makes React different from other methods of application building?

React is a library that focuses on JavaScript components and frameworks, giving developers an ample supply of useful code to implement into their applications. To answer this question, it's important for you to know the different types of application building techniques and the interfaces used. It's also necessary to understand where React fits in as part of the overall JavaScript framework.

Example: 'React is unique amongst JavaScript frameworks because it provides a library of pre-existing components for you to use. This can be of huge benefit when developing web applications, as rather than writing coding from scratch, it's ready to use from the library. This can help immensely when it comes to tight deadlines. React also doesn't guide the architecture like other frameworks, such as Angular. For example, when using Angular, you create things a certain way due to the runtime scripting. React offers more flexibility in this regard and allows you to develop interface architecture in more innovative and free-flowing ways.'

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2. Can you explain the difference between virtual DOM and real DOM?

This question is a test of your knowledge of document object models or DOMs. It's a fairly straightforward question that requires a good understanding of these two different types of models. Ideally, try to frame your answer around the core differences between these two models.

Example: 'One of the biggest differences in the context of React is that virtual DOM is often used instead of real DOM. This is because virtual DOM has several benefits over real DOM using the React library. Virtual DOM is much faster when it comes to updates and it uses JSX code for elements that are less memory-intensive. It's also a more cost-effective approach when compared to real DOM because it's less resource-intensive.'

3. What are the stateless components of React?

This question might confuse a few candidates because React is typically known for building interfaces with components that have a state. So the concept of stateless components doesn't usually coincide with React. With that said, there are some integrated stateless components, although they tend to provide a basic function within the code. So to answer this question competently, it's necessary to showcase your knowledge about these components.

Example: 'Although React is typically associated with components that have a state, there are certain functions that can render DOM with pre-existing properties. In React, stateless components are implementable, reusable functions. It doesn't require an internal stage due to the output, which acts as a function compiled of properties.'

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4. How familiar are you with Flux?

If you're asked a question that requires you to discuss familiarity or experience with a specific feature, you can apply the STAR method to answer the question comprehensively. The STAR method uses the following structure to answer these types of questions:

  • Situation: Describe the situation and any challenges you overcame.

  • Task: Outline your involvement in the task and the resolution.

  • Action: Discuss the actions taken.

  • Results: Describe the final results and the role you played in getting there. With the above question, the focus is on an architectural pattern known as Flux. Flux controls derived forms of data in a unidirectional manner to minimise traffic between components and data. React has several key Flux elements that developers often benefit from knowing, so it's a good idea to display your knowledge of this core feature.

Example: 'The Flux pattern uses a unidirectional flow of data actions and movements by allowing data modification from the 'Store', which is a central location in the architecture. When applying any changes, central dispatchers finish the process by sending the updated data to 'Views'. This can change the places where the end-user interacts with data. With Flux, you can only process a single action from the dispatcher's end at any given time, which is useful for data preservation, reliability and integrity.

My previous experience as a React developer involved MVC data flow, but over time issues developed due to a breakdown in the flow of data, which diminished the data's integrity. I then used the Flux architecture to resolve this issue, which resulted in better data reliability throughout the company and efficiencies in data flow. My changes empowered the business leaders to make better decisions through data insights.'

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5. What are your thoughts on JSX?

Many developers have strong opinions about JSX, so this is a relatively common question. JSX came alongside React as a new type of programming that can embed HTML code inside JavaScript snippets. The code itself isn't readable in the browser without transpiling it first. Due to this additional level of complexity, there's significant controversy around its usage in the industry. So answering this question can show that you're up to date with the latest trends in technology.

Example: 'JSX is a popular topic of debate in the industry, even though it's an optional feature of React. It's useful to an extent because it provides elements that can improve syntax, but there's a level of complexity to it that many people dislike. This is particularly true for veteran developers that use JavaScript because it deviates away from the standard process. In my opinion, it's worthwhile using JSX, assuming you've a team that's able to dedicate the time to configure it effectively.'

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6. Can you describe the lifecycle of React components?

The lifecycle of React is an important component that can add inherent value to businesses using this framework. When interviewing for roles that use React, it can be a good idea to discuss the component lifecycle to highlight your knowledge of this area. It also shows interviewers that you understand its importance to businesses.

Example: 'The lifecycle of React components is an incredibly important part of the framework for a company. Looking at it from a top-down perspective, there are three key features to consider. These are initialising, updating and destruction, which can provide a number of unorthodox approaches and uses. For example, at the initialising phase, there are actions such as getInitialState() or getDefaultProps() which are relatively abstract and very useful.'

What to expect in a React interview

If you're preparing for a React interview, there are several things to expect. To make sure you're ready for the interview, consider preparing for the following:

  • Interview questions: Most interviews contain verbal questions for you to answer, just like the ones outlined in this article. They could focus on several topics, such as behaviours, experience or technical skills. For React interviews, questions are most likely to focus on technical areas.

  • Testing: Interviewers might query your skills by testing you on React and JavaScript. This could involve solving issues with code snippets or devising ways to create interfaces in React. The interviewer might even ask you to explain certain aspects of coding.

  • Assignments: Some interviewers ask candidates to take home an assignment to gauge their competency in React. You usually receive this after the initial interview to further determine your eligibility for the role.

  • Multi-structured interviews: You can expect to have more than one interview, starting with a simple screening interview to match your skills to the role. From here, a second and even third interview may be necessary to further assess your aptitude to see if you're suitable for the role.

Please note that none of the companies, institutions or organisations mentioned in this article are affiliated with Indeed.

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