React Interview Questions: Secure a Mobile App Developer Career

ReactJS is a very popular library, especially amongst developers who are looking to build their mobile apps. Since the mobile applications market has been doing nothing else but rising in popularity, a lot of companies are looking for ReactJS-savvy developers to build apps and single-page websites. If you’re thinking that you would be suitable for the job and are preparing for your first job interview, you’re in luck - in this tutorial, I’d like to tell you about some of the most popular React interview questions.

We’ll talk about React itself - what it is, why people like it and use it, etc. Once you’ve got your footing set, and can at least imagine what to expect out of the interview, we’ll cover some of the more advanced interview questions on React JS.

The Main Basics About ReactJS

To give you a fluent start, let’s take a look at some of the more basic questions that you might encounter in your job interview. These are mostly definitions, comparison and “yes/no”-a type of question. Their main use is to test your fundamental knowledge to React.

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Question 1: What is ReactJS?

What an employer would usually want to do here is to check you’re thinking process. It’s quite obvious whenever a person is trying to come up with his definition of something, and when he’s simply reciting a text that he had memorized earlier.

Needless to say, the second option isn’t the better one. Anyone can memorize a given text - that’s isn’t one bit impressive. If you can explain difficult topics in React interview questions in an easily understandable manner, however - that’s something else! It shows that you have put in the time and the energy to study the subject, not just mindlessly memorize it.

So, to get back to the question at hand - what is ReactJS?

ReactJS is a front-end library. It’s based on JavaScript and was created by Facebook. The main purpose of this library is to provide developers with an all-around reusable UI.

Question 2: Why should we use ReactJS?

Knowing the features of a programming language means that you have in-depth knowledge about it. As you can probably tell, this is one of the more opinion-based React interview questions. You would do well, however, if you simply state some of the best features that are accredited to React. These include, but are not limited to:

• Virtual DOM instead of a real DOM;
• Fast and scalable;
• JSX provides a code that’s easy to both read and write;
• React is easily integrated with other JavaScript frameworks;
• etc.

Question 3: Explain ‘real DOM’ and ‘virtual DOM’.

DOM abbreviates as a Document Object Model. DOMs are used to understand certain specific texts. For example, when it comes to web and app development, DOM is used to represent the HTML texts.

ReactJS utilizes what is known as a virtual DOM. It is a simplified copy of React’s HTML texts. Moreover, it is a representation of the real DOM.

React providing and utilizing a ‘virtual DOM’ is often one of the main pros that are mentioned when talking about this JavaScript library. When it comes to your React interview questions, one of the possible follow-ups for the above-mentioned question might ask you to explain why ‘virtual DOM’ is superior to ‘real DOM’. The answer is pretty simple - virtual DOM is a lot faster and cheaper than the real one.

Question 4: What’s JSX?

JSX stands for JavaScript XML. ReactJS uses this file to make HTML codes easy to read and write. Additionally, JSX can boost the performance of your application or website.

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Question 5: What are ‘components’?

Components in ReactJS represent functions in JavaScript. They divide the React user interface into separate parts and make the UI reusable whenever the developer might need to.

Question 6: What are the stages of a component’s lifespan?

Although this could be seen as one of the more subjective React interview questions, there is still a consensus on the lifecycle of a ReactJS component.

There are three stages to such a lifecycle: initialization, updates of states and destruction.

Question 7: Is there a difference between a ‘component’ and an ‘element’?

Yes. A component in React accepts input and returns the element, which is simply a description of what you can see on your computer screen.

Question 8: Can web browsers read JSX?

No, no they can’t.

Web browsers are configured in such a way that they are only able to read JavaScript objects. Although similar, a JSX object isn’t the same as a JS object.

You can make it work, however. What you would have to do is simply transform the JSX object into a JavaScript one. Various converters can help you do this. After that, simply upload the object to the browser - it should be able to read it now. This kind of information will be very useful during the React interview questions.

Question 9: What’s the difference between ReactJS and React Native?

Through ought your interview, you are sure to get asked to compare ReactJS with some other library or framework. React Native interview questions are some of the more popular ones when it comes to this.

To put it very simply, ReactJS is simply a JavaScript library, while React Native is full-fledged, multiple feature-holding platforms where you can build your app from start to finish.

Question 10: What is ‘flux’?

Even though this relates more to JavaScript, it might still be one of your interview questions on React JS.

Flux allows you to create different layers of information (data) within your apps. Flux is important because it was designed by Facebook at the same time that they worked on React.

React Interview Questions - Advanced

Now that you can imagine what to expect out of the interview, let’s move on to some of the more advanced learning material.

These questions being advanced should tell you that you’re going to have to show some of the more in-depth knowledge that you have on React. Whether it be elaborating with your answer or demonstrating immense technical knowledge, anything and everything will help.

Question 1: How does ReactJS utilize ‘keys’?

React uses keys to differentiate between simple virtual DOM elements and those who are unique. Furthermore, keys help React recycle existing DOM elements so that the library would run and render smoother.

Question 2: Is there a difference between ‘container component’ and ‘presentation component’?

As already mentioned before, you will not avoid comparison React interview questions. Container components are focused on providing data to presentation and other container components. These components are concerned with maintaining the way that everything works.

Presentation components, on the other hand, are in charge of how things look. Whenever they obtain their own, personal state (which happens rarely), it is most often a UI one.

Question 3: What is ‘setState’ used for?

When you issue a ‘setState’ command, an object is merged into the current state. After this is done, the UI is updated according to the new set state.

This can be a great example of some of the more technical React interview questions.

Question 4: What does ‘render()’ do?

If we’re talking about a single element, then ‘render()’ returns it. When it comes to multiple elements, however, they would have to be grouped to do so.

Question 5: What are ‘synthetic events’ used for?

When it comes to React, synthetic events work in almost the same way that normal web browser events would. The only key difference is that synthetic events use a code that can be applied through ought multiple different browsers, while normal events only target a single browser.

Question 6: What is a ‘state’?

Believe it or not, this is considered to be one of the more difficult React interview questions.

Remember when we talked about the lifespan of a component? Well, states are objects that hold certain data within them. The main thing to remember here is that the data might alter through ought the lifespan of a component, depending on the events that influence it.

Question 7: What are ‘props’?

“Props” means “properties”. Parent-components provide props to their child-components for them to retain the frame of the application.

Question 8: What are ‘error boundaries’?

“Error Boundaries” in a function that allocates certain specific errors within the child-components, isolates them and then swaps the crashed area with a backup UI. In other words, error boundaries are like the saving grace for the developer if something doesn’t go according to plan.

Question 9: What’s an ‘arrow function’?

Since there is no default function to auto bind components in React, an arrow function allows the developer to associate contexts from two different components.

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Question 10: What’s ‘Redux’?

If you have a JavaScript app that is made whilst using flux, you may apply Redux as a container. In such situations, Redux becomes a predictable state container.

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Conclusions

I honestly hope that the React interview questions and answers that you found within the guide have motivated you to start learning and practicing for that job interview.

Since React is created and managed by Facebook, you can expect that a lot of the hype around it is at least somewhat inflated. Many developers might be interested in the library simply because it has such a popular, mainstream company attached to its name. However, these developers usually don’t tend to linger for very long. Their enthusiasm fades as soon as the “next big thing” hits the market.

That’s a good thing for you. If you’re passionate about React, this will show during the job interview. Whether you’re answering some React interview questions or simply describing components, your potential employers will see that you’re doing it with a passion. So don’t hesitate to give it everything you’ve got and shown the interviewers just how much you want to get that jo position.

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