Hello, everybody! It is not a secret that employers often ask different tricky questions on the interview. Even if you are a good specialist, you can be confused. So, if you are going to have an interview in React JS development company, you are in the right place. Today I will give you top ReactJS development interview questions and answers for 2020.

Question 1: Why should we use ReactJS?

As you can see, this question allows you to express your opinion about React JS. You can just name the best features of React and that will be enough. For example, they include:

Virtual DOM instead of real DOM;

React JS is a library that easily integrates with other JavaScript frameworks;

Speed and scalability;

JSX ensures code that is easy to read and write;

and so on.

Question 2: What is a JSX?

In the previous React JS question, we already mentioned clear JSX code as one of the advantages. But to understand what we are talking about, you need to understand what JSX is all about.

JSX means JavaScript XML. This file is used in ReactJS to make it easier to read and write HTML code. Besides, JSX can increase the performance of your app or site.

Question 3: Explain the distinction between Real DOM and Virtual DOM.

To understand some special texts DOMs are used. DOM is a Document Object Model. For instance, the DOM is used to represent HTML texts when it comes to web development.

In React it is used as a Virtual DOM. This is something in the nature of a simplified copy of React HTML texts. Furthermore, it is also a new presentation of a real DOM.

Virtual DOM is thought to be the main benefit of this JavaScript library. You may ask what the pros of Virtual DOM are. The answer is simple enough— Virtual DOM is considered to be much faster and cheaper than real.

Question 4: Can web browsers Read JSX?

No, they cannot.

Web browsers are configured to JavaScript objects only which can be read. This also means that the JSX object is different from the JS object.

However, you can solve this problem. You will just need to change the JXS object into a JavaScript object. Different converters can help you with this. After that, just load the object into the browser - now everything should work properly.

Question 5: What are the life cycle stages of components?

While this can be seen as one of the most subjective React interview questions, there is still a consensus around the lifecycle of React JS components.

This lifecycle consists of three stages: initialization, updating states, and destruction.

Question 6: What is the distinction between React JS and React Native? 

It is very important for you to know not only about ReactJS but also other available libraries and frameworks. For instance, React Native is also beginning to gain popularity, so it's also worth paying attention to.

With just the basics, ReactJS is only a JavaScript library, while React Native is a self-contained platform with different features that you can use to build your applications from start to finish.

Question 7: What is the key attribute for when rendering lists?

Keys help React determine which items have been modified, added, or deleted. They must be specified so that React can map the elements of the array over time.

The best way to choose a key is to use a string that will clearly distinguish the list item from its neighbours. Most often you will use the ID from your data as keys. When you do not have specified IDs for the list, you can use the element index as a key as a last resort.

Question 8: What is Redux?

Redux is a container with a predictable state for JavaScript applications based on the Flux design template. Redux can be used with ReactJS or any other view library. It is very compact (about 2 KB) and has no dependencies.

Question 9: What is the Flux?

Even though this is more about JavaScript, it's quite common to see React and Flux together.

Flux makes it possible for you to build various layers of information (data) within your apps. Flux is very important as it was created by Facebook along with React.

Question 10: What is setState used for?

When the setState command is called, the object is interfolded into the current state. As soon as this happens, the UI will be updated to the new state.

This question is a good sample of a more technical question on React.

Question 11: What is a State?

As strange as it may be, this question is considered to be one of the most difficult.

Remember how we talked about the lifecycle of a component? States are objects that include certain data within them. You have to remember here is that data can transform throughout the lifecycle of a component, depending on the events that affect it.

Conclusion

We have mentioned most of the React questions you might come across during an interview. In this post, you can find answers to ReactJS interview questions which are both the most basic and more advanced. So, now you are ready to interview)

If you learn all this information, you will be one step closer to your goal. Wish you all the best! Goodbye!