Top 65+ React Interview Questions and Answers in 2024

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React.js is one of the most in-demand JavaScript libraries for building user interfaces, especially for single-page applications. With over 1,44,000 job openings for React.js Developers globally, it has become a crucial skill in the web development industry. The average salary for a React.js Developer is approximately ₹10,00,000 per year. Below we have provided the top 75 React interview questions and answers.

Table of content

• React Basic Interview Questions for Freshers
• React Interview Questions for Experienced
• React Redux Interview Questions
• React Coding Interview Questions
• React JS MCQ Questions

React Basic Interview Questions for Freshers

1. Can browsers read a JSX file?

No, browsers cannot read JSX files directly. It can only read the objects provided by JavaScript. Now, to make a browser read a JSX file, it has to be transformed to a JavaScript object using JSX transformers, and only then it can be fed into the browser for further use in the pipeline.

2. Why is React widely used today?

React provides users with an ample number of advantages when building an application. Some of them are as follows:

• With React, UI testing becomes very easy.
• React can integrate with Angular and other frameworks easily.
• The high readability index ensures easy understanding.
• React can be used for both client-side and server-side requirements.
• It boosts application performance and overall efficiency.

3. Differentiate between Angular and React.

The difference between Angular and React is as follows:

4. What are events in React?

Whenever there are actions performed in React, such as hovering the mouse or pressing a key on the keyboard, these actions trigger events. Events then perform set activities as a response to these triggers. Handling an event in React is very similar to that in the DOM architecture.

5. What are Hooks in React?

Hooks are used to make use of the state and other features without having to explicitly write a class. Hooks were added to the React version, v16.8. The stateful logic can be easily extracted from a component, along with testing and reusing it. All of this is done without making any changes to the component hierarchy.

Check out our React Interview Questions video with Answers:

6. How can one print statements to the console in ReactJS?

To print statements in ReactJs, use console.log() similar to javascript.

7. What are tags in ReactJs?

Tags in ReactJs refer to the JSX elements, which allow us to write HTML like syntax in JS code snippets.

8. What is/are the debug tool/s for ReactJs?

Some tools to debug the ReactJs codes are:

1. React DevTools
2. React Developer Tools in Chrome DevTools
3. Redux DevTools Extension

9. What are forms in React?

Forms in React are used for collecting and managing user input. React forms can be created by
input, textarea, and select tags in React.

10. How are comments written in React?

There are two types of comments in react:

1. Single line comments are done using // outside JSX.
2. Within JSX multi line comments are put inside the curly brackets {/* */}

React Interview Questions for Experienced

11. What is React?

React is a widely used JavaScript library that was launched in 2011. It was created by developers at Facebook, and it is primarily used for front-end development. React uses the component-based approach, which ensures that you build components that possess high reusability.

React is well known for developing and designing complex mobile user interfaces and web applications.

12. What is the meaning of Virtual DOM?

A virtual DOM is a simple JavaScript object that is the exact copy of the corresponding real DOM. It can be considered a node tree that consists of elements, their attributes, and other properties. Using the render() in React, it creates a node tree and updates it based on the changes that occur in the data model. These changes are usually triggered by users or the actions caused by the system.

Next up among these React interview questions, you need to take a look at some of the important features that it offers.

13. What is the use of an arrow function in React?

An arrow function is used to write an expression in React. It allows users to manually bind components easily. The functionality of arrow functions can be very useful when you are working with higher-order functions, in particular. Consider the following example: //The usual way

 render() { return( ); } //Making use of the arrow function render() { return( this.handleOnChange(e) } /> ); } 

14. What is a higher-order component in React?

Higher-order components (HOCs) are a widely used technique in React for applying concepts that involve component reusability logic. They are not a React Native Firebase part of the React API and allow users to easily reuse the code and bootstrap abstraction. HOCs are also used to allow the simple sharing of behaviors across all of the components in React, adding more efficiency and functionality to the application.

React Interview Questions for 3 Years Experience

15. What are some of the important features of React?

React has multiple features that are used for unique purposes. The important ones are as mentioned below:

• React makes use of a single-direction data flow model.
• It deals with complete server-side data processing and handling.
• React uses a Virtual DOM, which has many advantages of its own.

16. What is the meaning of the component-based architecture of React?

In React, components are foundations used to build user interfaces for applications. With the component-based system in place, all of the individual entities become completely reusable and independent of each other. This means that rendering the application is easy and not dependent on the other components of the UI.

17. How does rendering work in React?

Rendering is an important aspect of React, as every single component must be rendered. This is done using the render() function. Once the function is called, it returns an element that represents a DOM component.

It is also possible to render more than one HTML element at a time by enclosing the HTML tags and passing them through the render function.

18. What are states in React?

States form is one of the vital aspects of React. It is considered a source of data or objects that control aspects such as component behavior and rendering. In React, states are used to easily create dynamic and interactive components.

19. What are props in React?

Props are the shorthand name given to properties in React. Props are read-only components that are immutable in nature. In an application, props follow a hierarchy that is passed down from parent to child components. However, the reverse is not supported. This is done to ensure that there is only a single directional flow of data at all times.

20. What is the difference between Props and States?

21. How are events created in React?

Events can be created very easily in React as shown here:

class Display extends React.Component({
show(evt) {
// Code inside
},
render() {
// Render the div with an onClick prop (value is a function)
return (</pre>
<div>Click Here</div>
<pre>);
}
});

22. How is routing in React different from Conventional routing?

Differences between conventional routing and the routing in React can be shown using the following aspects:

• Pages: Each view is considered as a new file in conventional routing while it is considered as a single HTML entity in React.
• Navigation: In conventional routing, users have to move across web pages for viewing. In React, the views are not refreshed as objects are re-issued to create new views.

23. What is the meaning of synthetic events in React?

Synthetic events in React are objects that act as cross-browser wrappers, allowing for the use of native events. This is done to ensure that a variety of browsers can run the API and that the event contains all properties.

24. What are stateful components in React?

Stateful components are entities that store the changes that happen and place them into the memory. Here, the state can be changed, alongside storing information such as past, current, and future changes.

25. What are refs in React?

‘Refs’ is short for references in React. Refs are used to store a reference to a single React element or React component. This is later returned using the render function.

They are mainly used in the following scenarios:

• To initiate imperative animations
• To join third-party DOM libraries
• To manage focus and apply media playback

26. What is the difference between shadow DOM and virtual DOM?

The difference between virtual DOM and shadow DOM is :

React JS Interview Questions for 5 Years Experience

27. What are some of the advantages of using create-react-app in React?

Making use of create-react-app is advantageous in the following ways:

• Support for JSX, ES6, and flow statements
• Already built and ready auto-prefixed CSS
• Fast interactive testing components
• Live development servers that help in debugging
• Scripts to handle JSS, CSS, and other files

Next up on these React Redux interview questions, you need to understand the meaning of Redux.

28. What are the three phases of a component life cycle in React?

The following are the three phases of a component’s life cycle:

• Initial rendering: This is the phase that involves the beginning of the journey of the component to the DOM.
• Update: Here, the component can be updated and rendered again if required after it gets added to the DOM.
• Unmounting: The final phase involves the destruction of the component and its eventual removal from the DOM.

29. Can AJAX be used with React?

Yes, any AJAX library, such as Axios and jQuery AJAX, can be used with React easily. One important thing is to maintain the states of the components, and here too, the props are passed from the parents to the child components.

Child components still cannot send back props to parents, and this factor greatly increases rendering efficiency when dynamic data is considered.

30. What are controlled components in React?

Controlled components in React refer to the components that have the ability to maintain their state. The data is completely controlled by the parent component, and the current value is fetched by making use of props. This is done to notify users of any changes that occur when using callbacks.

31. What are the predefined prop types present in React?

There are five main predefined prop types in React. They are as follows:

1. PropTypes.bool
2. PropTypes.func
3. PropTypes.node
4. PropTypes.number
5. PropTypes.string

The propTypes can be defined for the user component as shown below:

import PropTypes from 'prop-types';
class User extends React.Component {
render() {
return (
<h1>Welcome, {this.props.name}</h1>
<h2>Age, {this.props.age} ); } } User.propTypes = { name: PropTypes.string.isRequired, age: PropTypes.number.isRequired }; 

32. What is React Fiber?

React Fiber is a new engine in React. It is the core implementation core algorithm in React 16.

The main goal of React Fiber is to ensure that there are incremental rendering facilities for the virtual DOM. This increases efficiency when rendering animations, gestures, etc., and also helps in assigning priority to updates based on the requirement, thereby increasing overall efficiency.

33. What are forward refs?

In React forward refs, allow the component to pass down a ref to a child component. This feature allows the parent component to access the child component’s DOM node or React component instance.

34. What are the approaches for including polyfills in your create-react-app?

One can make use of Polyfill and create-react-app in multiple ways, like:

• Import the ‘index.js’ or ‘App.js’ file manually using the import statements.
• Using the polyfill.io service to automatically include polyfills based on the features of the app.
• Make use of libraries such as core-js or babel in ‘index.js’.

React Advanced Interview Questions for 6 to 10 Years Experienced

35. What are the disadvantages of using MVC in React?

Among a plethora of advantages of using MVC in React, there are minor problems as stated below:

• A lot of memory waste occurs
• DOM manipulation costs a lot.
• The application becomes slow.
• Lots of dependencies are created.
• The complexity of models increases.

Next up among these ReactJS interview questions is understanding pure components.

36. What are pure components in React?

Pure components are singular entities that are written in React. They are fast and simple to write and have the ability to replace a component that has only the render() function. This is done to ensure that the performance of the application is good and that the code is kept simple at the same time.

Next up on this top React interview questions blog, take a look at the questions categorized as advanced!

37. What are higher-order components (HOCs) used for?

HOCs are used for a variety of tasks such as:

• Manipulation of props
• State manipulation and abstraction
• Render highjacking
• Code reusing
• Bootstrap abstraction

38. What are the keys in React?

Keys are used in React to check all items and to track changes actively. They are used to directly check if an item has been added or removed from a list.

Consider the following syntax:

function List ({ todos }) {
return (
<ul>
{todos.map(({ task, id} ) => <li key={id}>{task}</li>}
</ul>
)
}

39. Differentiate between a controlled component and an uncontrolled component in React.

A controlled component, as the name suggests, is a component over which React has complete control. It is the singular point of data for the forms.

An uncontrolled component is one where the form data gets handled by DOM and not the React component. This is usually done using refs in React.

40. How can you tell React to build in production mode?

React can be coded to directly build into production by setting the process.env.NODE_ENV variable to production.

Note: When React is in production, warnings, and other development features are not shown.

41. What is the use of the second argument that is passed to setState? Is it optional?

When setState is finished, a callback function is invoked, and the components get re-rendered in React.

Yes, the setState function in programming allows for an optional argument, typically a callback function, since it operates asynchronously. However, it is generally considered best practice to utilize alternative lifecycle methods instead of relying solely on this approach.

Next up on this top React interview questions and answers blog, you need to take a look at binding.

42. Is there a way to avoid the requirement of binding when using React?

Yes, there are two main ways you can use to avoid the need for binding. They are as follows:

• Defining the Event Handler as an Inline Arrow function:

class SubmitButton extends React.Component {
constructor(props) {
super(props);
this.state = {
isFormSubmitted: false
};
}
render() {
return (
<button onClick={() => {
this.setState({ isFormSubmitted: true });
}}>Submit</button>
)
}
}

• Using a function component along with Hooks:

const SubmitButton = () => {
const [isFormSubmitted, setIsFormSubmitted] = useState(false);
return (
<button onClick={() => {
setIsFormSubmitted(true);
}}>Submit</button>
)
};

Also, the Event Handler can be defined as an Arrow function, which is eventually assigned to a Class Field to obtain similar results.

43. What is the StrictMode component used in React?

The StrictMode component, when used, would benefit users immensely while creating new codebases to understand the components being used.

However, it can fit well in debugging as well because it will help solve the problem faster when it is wrapped with other components, which could be causing the problem.

Next up on these interview questions on React JS, you have to understand how to speed up rendering.

44. What would you do if your React application is rendering slowly?

The cause of slow rendering in React is mostly because of the number of re-render operations, which are sometimes unnecessary. There are two main tools provided by it to help users here:

• memo(): This is used to prevent all of the unnecessary re-rendering carried out by the function components.
• PureComponent: This is used to ensure that the unnecessary re-rendering of class components is avoided.

45. Can you conditionally add attributes to components in React?

Yes, there is a way in which you can add attributes to a React component when certain conditions are met.
React has the ability to omit an attribute if the value passed to it is not true.

Consider the following example:

var condition = true;
var component = (
<div
value="foo"
{ ...( condition && { disabled: true } ) } />
);

46. Why are props passed to the super() function in React?

Props gets passed onto the super() function if a user wishes to access this.props in the constructor.

Consider the following example:

class MyComponent extends React.Component {
constructor(props) {
super(props)
console.log(this.props)
// -> { icon: 'home', … }
}
}

47. What is the difference between using getInitialState and constructors in React?

When using ES6, users must initialize the state in the constructor and the getInitialState method is defined. This is done using React.createClass as shown in the below example:

class MyComponent extends React.Component {
constructor(props) {
super(props);
this.state = { /* initial state */ };
}
}

This above piece of code is equivalent to the following:

var MyComponent = React.createClass({
getInitialState() {
return { /* initial state */ };
},
});

Next up among these interview questions on React JS, you have to know what predefined props are.

48. Do you have any certifications to boost your candidacy for this React.js role?

With this question, the interviewer is trying to assess if you have any technical experience through learning and implementation. It is always advantageous to have a certification in the technology that you’re applying for.

This creates an impression that you have put your time and effort into learning and implementing the technology. Alongside adding a lot of value to your resume and your knowledge on the topic, it can be used to obtain a well-coveted job in the market!

49. What is the purpose of a callback function as an argument of setState()?

The setState() function is an asynchronous function and can have performance issues. To avoid the lag in performance, a callback is used that ensures that the provided function gets executed after the state has undergone an update and the component has re-rendered.

50. How to bind methods or event handlers in JSX callbacks?

In Jsx callbacks to bind the event handlers, you can bind methods or event handlers utilizing the arrow function syntax by explicitly binding them in the constructor.

Binding with the Arrow Function 

Explicit binding through the constructor

React Redux Interview Questions

51. What is the meaning of Redux?

Redux is used to store the state of the application in a single entity. This simple entity is usually a JavaScript object. Changing states can be done by pushing out actions from the application and writing corresponding objects for them that are used to modify the states.

For example:

{
first_name: ‘John’,
last_name : ‘Kelly’,
age: 25
}

All of the data is retained by Redux (also called a store).

52. Differentiate between Flux and Redux in React.

53. What are the components of Redux in React?

Redux consists of four main components as shown below:

• Action: An object that describes the call
• Reducer: The state change storage unit
• Store: The state and object tree storage
• View: Displays data provided by the store

54. What are the advantages of using Redux?

There are many advantages of Redux, and some of them are as given below:

React Coding Interview Questions

55. What does the code do?

function App() {
  const [count, setCount] = useState(0);
 useEffect(() => {
console.log("Component rendered successfully");
  }, []);
   return (
<div>
   <button onClick={() => setCount(count + 1)}>Click me</button>
   <p>You clicked {count} times</p>
</div>
  );
}

This App program creates a increment function on the rendering of useState and useEffect hooks used, on click it increments the count and logs a message.

56. Find the error in the code:

import React from "react";
 function App() {
  const names = ["Brian", "Paul", "Krug", "Halley"];
   const listItems = names.map((name) => <li>{name}</li>);
   return <ul>{listItems}</ul>;
}
export default App;

In React the map and key functions help in rendering the components. The issue in the code is that the key is not assigned to the <li> element inside the map function to render properly.

57. Analyze the below code and advise what is wrong with using setState() inside the render() method.

import ReactR, { Component } from "react";
class App extends Component {
state = {
counter: 0,
};
render() {
this.setState({ counter: this.state.counter + 1 });
return <div>Counter: {this.state.counter}</div>;
  }
}
export default App;

The setState usage in the above code has been implemented in render() which leads to infinite loops. This causes the state of the program to be updated each time the components are rendered,and this continues with each trigger, leading to infinite loops.

58. What would be the log on the console?

class App extends React.Component {
  state = { count: 0 };
handleClick = () => {
this.setState({ count: this.state.count + 1 }, () => {
   console.log(`Count: ${this.state.count}`);
    });
};
 render() {
return (
  <div>
   <h1>Count: {this.state.count}</h1>
   <button onClick={this.handleClick}>Click me
   </button>       
    </div>  
     );
  }
}

The above program, on each button click, prints the log message as:
(If the button is clicked 2 times)
Count: 1
Count: 2

59. What is the purpose of the below code:

import React from 'react';
class AlertExample extends React.Component {
handleClick = () => {
alert('Hello! This is an alert pop-up.');
};
  render() {
return (
  <div>
<h1>Alert Example</h1>
<button onClick={this.handleClick}>Show Alert</button></div>
  );
}
}
export default AlertExample;

The above programme creates an Alert Message when the program is rendered.

React JS MCQ Questions

60. Which is used to increase performance in React.js?

1. Virtual DOM
2. Original DOM
3. Both A and B
4. None of the above

Virtual DOM

61. React.js is a?

1. Server-side framework
2. User-interface framework
3. Both a and b
4. None of the above

User-interface framework

62. How can data be passed to components from outside?

1. Render with arguments
2. setState
3. PropTypes
4. props

props

63. Is ReactJs a framework or library:

1. Library
2. Framework
3. Both a and b
4. None of the above

Library

64. Babel is a?

1. JavaScript compiler
2. JavaScript interpreter
3. JavaScript transpiler
4. None of the above

JavaScript compiler

65. Which option is used to display a pop up?

1. alert()
2. popup()
3. Message()
4. None of the above

alert()

66. Is React.js a Frontend or backend framework?

1. Front-end
2. Back-end
3. Both a and b
4. None of the above

Front-End

67. What is the port used by default for webpack-dev-server runs?

1. 3000
2. 8804
3. 3030
4. 8080

 8080

68. What is the number of elements a valid react component can return?

1. 1
2. 2
3. 5
4. 10

1

69. Are props used to pass data from parent to child components?

1. True
2. False

True

React Developer Salary Trends

The demand for ReactJS developers has tripled in the past few years, both in India and abroad. According to Glassdoor, the average salary for React developers in India ranges from Rs 5.4 LPA to 12 LPA, with additional cash compensations from Rs 6K to Rs 1 LPA.

According to Glassdoor, the average salary for a React developer in the US is $100K, with an average supplemental pay of $10K.

React Developer Job Trends

When we talk about lucrative careers in web development, we can observe that ReactJS reigns supreme with surging demands in companies like Facebook, Myntra, Amazon, Walmart, Microsoft, and many others both in India and abroad.

1. Demand: According to India Today, React JS makes it to the top 5 most demanding digital skills, with an 184% shift in the past year.
2. Global Demand: According to LinkedIn, there are more than 36,000 openings in ReactJs, with 1860 more jobs in the United States.
3. Regional Demand: According to LinkedIn, India has seen an upsurge of more than 26,000 new opportunities.
4. Popularity: ReactJs remains the most popular library, with a market share currently over 40%. According to the State of JavaScript 2022 survey, 69% of developers have used ReactJs and 54% claim they would reuse the JavaScript library.
5. Development: ReactJs not only comes in handy in frontend development but also mobile development. According to the State of JavaScript 2022, React Native has been utilized by developers as per past reports.
6. Future Scope: Constant updates in the ever-growing community of ReactJS ensure the growth of high-paying remote jobs. India currently has the second-largest pool of React developers globally, with over 1.5 million skilled developers.

React Developer Roles and Responsibilities

MakeMytrip ReactJs Developer is responsible for:

• The developer is responsible for turning broad conceptual ideas into smooth congruent scenarios, usable flows, and simple intuitive interfaces.
• The developer will be responsible for creating wireframes, storyboards, user flows and process flows to effectively communicate interaction and design.
• Develop the user experience strategy for the product and drive the overall design solutions based on usability, consistency, business goals, time to market, and customer experience.

We hope these Full Stack development course interview questions will help you prepare for your upcoming interviews. If you are looking to learn Full Stack developer course in a systematic manner with expert guidance and support then you can check our Full Stack developer course with placement guarantee.