What To Ask React.js Developer During The Interview: Common React.js Interview Questions and Answers

We will describe what React is, why people like to work with it and much more. After that, we will move on to the frequently asked basic react.js interview questions (for interviewing juniors) and interview questions to ask react.js developer, who is more experienced (for middle and senior React).

Let's consider basic interview questions on react.js and topics that will be useful for interviewing beginners who just have started their careers. They mainly relate to definitions, comparisons, and yes / no situations. They are necessary only to test the essential knowledge of the developer without technical tasks.

Question 1: What is React JS?

This question helps to understand which of the candidates responds with memorized definitions, and who really understands what they are talking about.

If a developer can explain complex topics in a simpler and more understandable manner, then this is already worthy of respect and attention! This shows that they really invested time and energy in studying this area of programming.

So, back to the question - what is React JS?

React JS is a front-end library. It is based on JavaScript and is maintained by Facebook. The main purpose of this library is to provide developers with a universal reusable UI.

Question 2: Why Should We Use ReactJS?

This question allows the developer to give their opinion on React JS. It’s enough that the candidate simply names the best features of React. For example, they include:

• Virtual DOM instead of the real DOM;
• Speed and scalability;
• JSX provides code that is easy to read and write;
• React JS is a library that integrates seamlessly with other JavaScript frameworks;
• Etc.

Question 3: Explain the Meaning of Real DOM and Virtual DOM.

DOM stands for Document Object Model. DOMs are used to understand certain specific texts. For example, when it comes to web development, the DOM is used to represent HTML texts.

ReactJS uses something called Virtual DOM. This is a kind of simplified copy of React HTML texts. Moreover, it is also a representation of the real DOM.

The provision and use of Virtual DOM in React is often considered a major benefit of this JavaScript library. Then what is the advantage of Virtual DOM? The answer is very simple - Virtual DOM is much faster and cheaper than real.

Question 4: What is JSX?

In the answer to the React JS question mentioned above, we have already given clear JSX code as one of the advantages. But in order to understand what is at stake, you need to be aware of what JSX is all about.

JSX stands for JavaScript XML. ReactJS uses this file to make HTML code easier to read and write. In addition to this, JSX can improve the performance of your application or site.

Question 5: What are the Components?

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

Question 6: Is there a difference between a component and an element?

Yes. A component in React accepts input and returns an element that is simply a description of what you see on the computer screen.

Such questions are intended to confuse the developer.

In addition to understanding the library, you can also appreciate the candidate's attentiveness.

Question 7: Can Web Browsers Read JSX?

No, they can’t.

Web browsers are configured to read only JavaScript objects. Which also means a difference between a JSX object and a JS object.

However, this problem can be solved. You will just need to transform the JXS object into a JavaScript object. Various converters can help with this. After that, you just need to load the object into the browser.

Question 8: What is the Difference Between React JS and React Native?

It is very important that a would-be member of your team knows not only about React JS, but also other popular libraries and frameworks, for example, React Native.

We can highlight the main difference - ReactJS is a JavaScript library, while React Native is a self-contained platform with various functions that you can use to create your applications from scratch.

Question 9: What is Flux?

Although this is more relevant to JavaScript, you can pretty often see React and Flux together.

Flux allows you to create different data layers within your applications. Flux is very important since it was developed by Facebook along with React.

Now you already know the basic questions on this topic, so it's time to find out why React JS is a very functional and advanced library and ask react.js senior interview questions.

These react.js developer interview questions are called advanced only for the reason that they require the candidate to have more in-depth knowledge of React.

Question 1: How React JS Uses Keys?

React uses keys to draw the line between simple virtual DOM elements and those that are unique. Additionally, keys help React recycle existing DOM elements to make the library work and render more smoothly.

Question 2: Is there a Difference Between Container Components and Presentation Components?

Container components aim to provide data for presentation and other container components. These components are related to maintaining how everything works.

Presentation components, on the other hand, are responsible for how things look. Whenever they get their personal status (which rarely happens), they are most often UI.

Question 3: What is setState used for?

When you call the setState command, the object merges into its current state. As soon as this happens, the UI will be updated in accordance with the new state.

This is a good example of one of a more technical senior react.js interview questions.

Question 4: What does render () do?

If we are talking about a single element, then render () returns it. When it comes to several elements, they must be grouped for this.

Question 5: What Are Synthetic Events Used For?

It is one of the most interesting react.js senior developer interview questions. If we are talking about React, then synthetic events work just like regular web browser events. The only difference is that synthetic events use code that can be applied to many browsers, while normal events target only one.

Question 6: What is a State?

Strange as it may be, this issue is considered one of the most difficult.

Remember how we talked about the component life cycle? Well, states are objects that contain certain data inside them. The main thing to remember here is that the data can change throughout the component’s life cycle, depending on the events that affect it.

Question 7: What is Props?

Props means properties. Parent components provide properties to their child components in order to preserve the application format.

Question 8: What are Fuses?

Error Boundaries or Fuses are a function that distributes certain specific errors in child components, isolates them, and then replaces the alarm area with a backup UI. In other words, fuses are a kind of backup plan for the developer if something goes wrong.

Question 9: What is Arrow Function?

Since React does not have a function for automatically linking components by default, the Arrow Function allows the developer to link contexts from two different components.

This is what top advanced react.js interview questions look like.

Web application development on React.js is one of the key expertise at Geniusee. This is due to the fact that:

• It allows you to create components in your code that can be reused without rewriting the code.
• Speed and scalability;
• It is easily adaptable, easy and convenient to use.
• This library is easy to understand and master, therefore, it allows teams to work faster.

Thanks to the extensive experience of our specialists and the wide functionality of the React JS library, you will get:

• high-quality web application with high page loading speed;
• fast website, the performance of which will be high even with the maximum influx of traffic;
• a multi-platform application that will display equally well on all devices;
• a project that can be easily ported to iOS and Android mobile platforms using React Native;
• a web application that is easy to maintain (even if one module fails, the impact on the entire site will be minimal).

The ability to reuse written code in React JS allows you to create a web application without any errors, because the less code you need to write, the less likely there will be a shortcoming in coding. If you decide to order the creation of an application in React JS in Ukraine, you will receive it as quickly as possible!

Let's take a look at the stages through which we will walk with you.

1. Contacting the company

First of all, you contact Geniusee in any convenient way, tell about your business, share your wishes and requirements regarding the future project.

2. Market research

Further, our specialists will study the market in which your business operates in order to create a web application that meets all modern trends.

3. Design stage of all business processes

We will provide everything from A to Z and will make a full lifecycle project that requires minimal financial investment on your part.

4. Estimation of the cost of services

The price directly depends on the complexity of the future web application. In any case, we will come to a compromise by assigning a fee that satisfies both you and us.

5. Prototyping

You will see what the future web application will look like, and if you wish, you can make the necessary edits.

6. Development stage

Our experts create a project taking into account all the recommendations from you and send you the result within the agreed period.

7. Testing and optimizing a web application

If errors occur during its use, the developers of the Geniusee company promptly eliminate them.

8. Technical support

Next, your web application is fully functional. For our part, we provide full technical support and even make improvements if necessary.

So, we have covered most common interview questions for react.js developers that you can ask during the interview. You have learned the answers to both the most basic and more advanced ReactJS questions.

Naturally, covering all issues would be too impossible a goal. However, if you understand the issues and topics of this guide, you can confidently conduct interviews with developers and assess their level of understanding in React.js.

Fill out the contact form or send us an email to info@geniusee.com and we'll start building a really high-quality web app for you! Geniusee is a team of professionals capable of making all the wishes of their clients come true. We are looking forward to our joint cooperation!