10 React Interview Questions to Practice

10 Respond to interview questions for practice

React is an open source JavaScript framework developed by Facebook. It is currently the most popular front-end frame used today. Its success even convinced Facebook to develop React Native, another framework that uses React for mobile development across platforms.

When you go to interview for a job that requires you to use React daily, employers want to know that you have the necessary skills to get the job done. This means that your interview is likely to include React interview questions, and while we can not guess exactly what they will ask, we have compiled some of the most popular ones here along with possible answers.

1. What is React and how does it differ from other JavaScript frameworks?

With this question, the interviewer wants to find out if you know about the JavaScript ecosystem in general and what makes React unique. One thing you could mention is that while some developers call React a framework, many consider it a library and not a complete framework.

This is because React’s purpose is to build UI components for your web app. That’s all it really does. It is the V (or View) part of an MVC (Model, View, Controller) architecture, and to build a complete application with React, you need other libraries like Redux.

Most JavaScript frameworks, like AngularJS, have tools for creating controllers, directives, services, and other features. With these other frameworks, you mostly have to use the tools you get. With React you can build an application with the libraries of your choice.

2. What is JSX?

JSX is a language that React uses to embed an HTML template in code. It is not understood by browsers and must be transfixed with tools like webpack and Babel before it can be run.

Still, JSX helps streamline React development once you know its syntax. You do not actually need to use JSX to create React components and can use React.createElement() instead, but Facebook recommends using JSX. Most React developers prefer its declarative syntax, and it also reduces code complexity.

Here is an example of JSX:

Hello World!

3. What is the state of React?

State is a JavaScript object used to represent the data stored in a React app, which may change over time. For example, you might have a state variable called clicks which is updated when a button is pressed.

Mode is fully contained in the component, unlike props. In class components, you use the state class variable to set a state variable, as in the example below:

class User extends React.Component { constructor(props) { super(props)
this.state = { greeting: 'Hello World!' } 
render() { return ( 
) } } 

In functional components you can set the mode of the component with useState hook:

const User = () => { const [greeting, setGreeting] = '';
setGreeting('Hello World!');
return ( 
); } 

4. What are the props in React?

Props are input to components and a way to transfer data from one component to a child component. They can be individual values, objects or functions. Here is an example:

const User = () => { const [greeting, setGreeting] = '';
setGreeting('Hello World!');
return ( 
); } 

In the example above is MyHeader component is passed greeting props and can be accessed inside this component with props.greeting.

5. What are the three main phases of the life cycle of a React component?

They are:

  1. The initial reproduction phase, when the component is changing the DOM of the web page.
  2. The update phase after the component is added to the DOM and updated only when its state or props change.
  3. The dismantling phase, when the component is damaged and removed from the DOM.

6. What are synthetic events in React?

React wraps the browser’s native events with its own cross-browser compatibility event structure. It has the same API as browser events, but works the same way in all browsers.

7. Where is it necessary to use a key prop and why?

Key props are required when creating a variety of items. React uses this key to identify specific elements in the array when they are updated, removed, or added.

8. What is a ref in React?

ONE ref (reference) in React is an attribute that gives you a handle to access the functions of a specific element. Here is an example:

const User = () => { const ref = React.useRef();
return ( 
); } 

The code above will focus the cursor in the input using a ref.

9. What are Higher-Order Components (HOC)?

Higher-Order components are custom components that pack other components into them. They can dynamically accept one or more components as children without changing or copying any of the children’s behaviors. They allow for the reuse of code and state abstraction and manipulation.

10. What are pure components?

Pure components in React are not reproduced when props or modes are updated to the same value. You can extend React.PureComponent class to use them. Rendering is limited in this way for higher performance and is often used for components that are primarily for display.

Learn more about React

Do not worry about preparing for all sorts of questions you may come across during your interview. That would be impossible. Instead, focus on strengthening your understanding of React’s concepts and functions, and if you need a refresher, try courses such as:

But keep in mind that even though the company you are interviewing with is heavily dependent on React, they are likely to test your knowledge of other programming tools and features. You may even be asked to conduct a technical interview. For more information on interviews in the technology industry, check out the articles below. Then visit our Career Center for more tips on how to prepare.

Interview preparation courses and tutorials | Code Academy

Interview is an important step in your journey towards getting a job in tech. Technical interviews allow you to showcase your skills and knowledge, but practice is key. You need to understand technical concepts and be prepared to talk through solutions with your interviewers.


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