Top-16 React JS interview questions

Nowadays react interview questions are becoming one of the most popular topics for future developers. It is easily explained. React JS is one of the most popular and influential JavaScript platforms and the most popular front-end framework of recent times. That is why I’d like to represent the topic – top-16 React JS interview questions.

 With such the popularity and level of penetration in all companies, either start-ups or large corporations, there are many opportunities to get a job if we master this framework. 

In this article you will find the most frequently asked React interview questions and, of course, the best answers for them. I divided all the questions into two groups. 

 I divided all the questions into two groups. You will have an opportunity to study the basic questions first, and then follow the advanced ones. So, you will have an idea of ​​what interview questions you may be asked in small organizations as well as huge corporations.

Thus, my article will be interesting and useful both for beginners and more experienced developers, and for interviewers. So, if you want to get a job as a React JS developer, it’s a good idea to study these React JS interview questions and answers.

Reаct JS bаsic intеrview quеstions. 

I suppose any interview starts with the basic questions whether you are interviewed in а small company or a huge organization. Your answers should be laconic and clear. Don’t be surprised if an employer asks you such an easy question. He may just check your reaction and understanding of this topic.

It’s not worth mentioning that the first impression is very important. Anyone can remember a text and it’s not a great thing that can surprise anyone. But if you can explain complex topics in a simpler and more comprehensible way, it is really worthy of respect and attention.

This shows that you dedicated much time and made a great effort to study this area of programming.

1. Describe the React JS working process.

React JS is a front-end library, which works on the basis of JavaScript and is supported by Facebook. It is aimed at expanding complex interactive user interfaces in mobile and web apps. 

2. What is the usefulness of React JS?

As you understand, this question gives you an opportunity to express your own opinion on React JS. You can just list the features of React JS you like most of all. For example:

  • Virtual DOM vice Real DOM;
  • Speed and scalability;
  • JSX supplies code, easy for reading and writing;
  • React JS easily integrates with other JS frameworks;

3. What problem does React JS solve?

React makes a virtual DOM. When the state modifies the component, it first runs the «differences» algorithm, which defines the modifications in the virtual DOM. Then it aligns the DOM with the difference comparison results.

4. Describe Real DOM and Virtual DOM? Define their benefits?

DOM means Document Object Model. DOM is used to realize particular texts. For example, concerning web development, DOM represents HTML texts.

React JS uses something called Virtual DOM. It’s a kind of simplistic copy of React’s HTML texts. Moreover, it represents the Real DOM. So, the advantage of the Virtual DOM is obvious. It is much faster and cheaper than the real one.

5. Explain Components in React JS?

React JS Components are functions in JavaScript. They divide the React JS user interface into distinct parts and allow the developer to reuse it at any time.

6. What Phases of the React Components Life Cycle can you name? 

Although this may be regarded as one of the most subjective issues of the React interview, there is still a consensus on the React components’ life cycle.

Such a life cycle consists of four phases: InitializationMountingUpdatingUnmounting.

7. Establish the distinction between controlled and uncontrolled Components

  • A controlled component accepts the current meaning via properties and notifies changes through reverse calls such as onChange. The parental component “controls” it, processing the return call and operating its state and transmitting new values as requisites of the controlled component. You can also call it a “mute component”.
  • An uncontrolled component keeps its internal state, and you query the DOM with the help of “ref” to find its current value when you need it. It looks like a traditional HTML.

 Almost in all cases, you use controlled components.

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Advanced React interview questions.

You’ve studied the most basic React JS questions and answers, so it’s time to find out why React JS is an advanced framework.

 These issues are called advanced because they require from you deep knowledge in the React sphere. 

8. Say a few words about Flux?

Although this is more relevant to JavaScript, it is quite common to see React and Flux together.

 Flux gives you an opportunity to establish different layers of data inside your applications. Flux is very important as it was designed by Facebook together with React.

9. What way does React JS use keys?

React JS uses keys to draw a line between simple virtual DOM elements and unique ones. Besides, keys help React JS to recycle existing DOM elements to make the library work and display more smoothly.

10. What does render do?

Render returns a single element and group together several elements.

11. What is State?

It seems to be strange but this question is considered to be one of the most difficult ones.

 Do you remember what we’ve talked about the life cycle of the component? Well, states are the objects that have certain data inside them. The main thing you should remember is that data can change over the entire life cycle of a component, depending on the events that affect it.

12. Let’s talk about Props. What are they?

Props are abbreviated from properties. Parental components provide properties to their child components to save application format.

13. What’s the distinction between State and Properties?

Props are JavaScript objects and states as well. They both contain data that affect rendering results, but they differ in functionality concerning the component, i.e.:

  • The prоperty is transmitted to a component in the same way as the function parameters
  • The state is managed inside the compоnent in the same way as variables declаred inside a function.

14. Whу dо we usе React JS propTypes?

If you’d like to chеck the types in your аpp, you may use Flow or Typescript (JavaScript extensions). But if you do not want to use these JS extensions for one or another reason, React JS has several built-in type testing capabilities.

To launch type checking for component props, you can assign a special property called “React JS propTypes”. PropTypes exports many validators to ensure that the information, you get, is valid. This will help you to avоid future errors and problems in development when the app gets larger. It also makes the code readable as we can see how to use each component.

15. What do we use setState for?

When you call setState, the object is combined in the current state. As soon as it happens, the UI will be upgrаded to the new state.

 This question is a great exаmple of a more technical question on React JS.

16. What are Hooks? In what version of React JS did they appear?

Hooks are functiоns by whіch you cаn «catch» to the stаte and methods of the React life cycle from functional compоnents. Hooks do not work inside classes – they give you the possibility to use React without classes. 

React contains several built-in hooks such as useState. You can also build your hooks to reuse them in your other components. Hooks are an innovation in React JS started with version16.8 


So we covered most of the React JS questions that you can be asked at the interview. Here you have got answers to both the basic and more advanced questions about React JS.

Of course, to cover all the issues would be a too fantastic goal. However, if you deal with these issues and topics, you will be one step closer to your goal.

I hope, you have found the answers to all the questions you are interested in and now you can boldly start practice and training.

And lastly, a few general recommendations. Don’t overdo it. There’s no need to spend the night on a flight to study this topic, so your employer can see your laps under your eyes.

I hope you have enjoyed the topic: “Top-16 React JS interview questions” and received some valuable and helpful information.

Sleep well and find a more effective way to learn and practice (make short notes, for example) and relax! Try not to get too worked up before your interview. It’s okay to be a little nervous before an important event – but not to be on edge.

If you are a fan of your job or have a hunger for a new piece of knowledge, I’d like to recommend you reading this article as well: Vue: The Dark Horse Of Front-End Development.

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