ReactJS is a very popular library, especially among companies that want to create their own mobile applications. And since the mobile industry has recently shown nothing but rapid growth, many business owners have become interested in developers who are able to work effectively with React JS to create applications and one-page sites. If you have decided that you need a React.js developer in your team, then you should prepare for an interview. In this guide, we will cover the questions you should ask during a React interview.
What to ask React.js developer during the interview.
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We will describe what React is, why people like to work with it and much more. After that, we will move on to the basic questions (for interviewing juniors) and advanced one (for interviewing middle and senior React).
Let's consider basic questions 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 basic knowledge of the developer.
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?
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;
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.
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.
Question 5: What are the Components?
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.
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.
Question 9: What is Flux?
Flux allows you to create different data layers within your applications. Flux is very important since it was developed by Facebook along with React.
React JS Interview Questions - Advanced
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.
These 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 a more technical question on React.
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?
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.
So, we have covered most of the React.js questions 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.