Common React JS Interview Questions + Tips for Answering

react js interview questions

The job interview is stressless only when you are the employer. When you hire javascript developers, you approach the interview with a list of questions, knowing all the correct answers and assessing how well your candidate performed. 

It’s different for the developer, though. There is always some stress going on because you can never be sure for 100% what type of questions to expect. 

Well, if you’re about to head off to your next major React JS interview, then we’ll help you to be more prepared and ready to answer all the questions. 

And no, we won’t be wasting much of your time. Let’s get straight to the topic: 

5 Common React JS Interview Questions

1) What is React? 

Yes, we know this is basic, but the chances are that your interview will start with a really simple question like this one: what is React

Of course, if you are applying for a Rect JS developer position, it is obvious that you know what React is. However, many employers will still choose to ask it to understand whether you can at least define it properly or not. 

So fi you are asked what React is, your answer should be something like this: 

React is a JavaScript library that was developed by Facebook back in 2011. It is using the component-based approach and is perfect for creating UI components that can later be reused. It is also perfect for the creation of interactive UI both for web and mobile. 

2) What are the main features of React? 

Next in the list will probably be to list the most prominent features of React JS. We’ll list it for you here, so in case you get a similar question, you know what to answer: 

  • JSX 

JSX is used to describe how the UI should look like. It helps to write HTML structures using the same file, which is written in JavaScript. Basically, it is an extension to the JavaScript syntax that provides you with a method for structure component rendering in a syntax that developers are familiar with. 

  • Components

These are the building blocks for all the React applications. One React app usually has various components. The components are crucial because they help break the UI into different independent pieces that can be reused and treated separately. 

  • Virtual DOM

React uses a more lightweight version of the real DOM that is called the virtual DOM. Why does React need a virtual DOM? Well, when the state of the object changes, the virtual DOM allows changing only that object in the real DOM instead of updating all of them. 

3) Why are browsers not able to read JSX? 

This one is among more technical questions. Once you define React and name some of its features, you’re going to get a little more in-depth questions. One of them can ask you to explain why browsers can’t read the JSX. Your answer, in this case, can be: 

Browsers can read JavaScript objects, but JSX is not considered a regular JavaScript object. So if we want the browser to read the JSX, we need to transform it into a JavaScript object. For this, there are JSX transformers like Babel. 

4) How is a state used in React, and what is it? 

We’ll get straight to the answer: 

In the core of React components are states. They are the source of the data that should be kept pretty simple. In other words, they are the objects that define how components are rendered and determine their behavior. States, unlike the props, are mutable and are used to create interactive and dynamic components. 

You call states with this.state().

5) What are HOC-s?

This question is the last one on our list, and it should also be among the last ones in the interview. Let’s start with the first part of the question: What are HOC-s? HOC stands for Higher Order Components, which is an advanced way to reuse the component logic. 

You can say that HOC is a pattern that is received from the compositional nature of React. It is able to accept the provided child component but cannot copy or modify it. In other words, HOC-s are the “pure” components. 

Sum up

Of course, these are only five questions, but they help you get the main idea of what to expect in the React JS interview. So take some time, revise all the definitions and React problems, and step into the interview confidently! 

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