Frequently Asked React Interview Questions

React JS is an open-source JavaScript library that is widely used for building user interfaces for web applications. It was developed by Facebook and is maintained by a community of developers. Frequently Asked React Interview Questions uses a component-based architecture, which makes it easy to build complex and interactive UIs. With React, developers can build reusable UI components and compose them together to create a full-featured web application.

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Frequently Asked React Interview Questions -1

1. What do you mean by ReactJS?
It is a server-side framework
It is a user-interface library
both A and B
none

2. How to pass data to components?
render with arguments
setState
PropTypes
props

3. Who created React.js?
Jordan Mike
Jordan Walke
Tim Lee
Jordan Lee

4. Which language is used in React.js?
Python
Javascript
java
Php

5. Identify the command used to create a react app.
npm install create-react-app
npm install -g create-react-app
install -g create-react-app
None

6. State whether true or false: React.js covers only the view layer of the app.
True
False

7. What is ReactJS mainly used for building?
database
connectivity
user interface
design platform

8. Which of the following is the correct name of React.js? React
React.js
ReactJS
All of the above

9. How many numbers of elements a valid react component can return?
1
2
4
5

10. A state in React.js is also known as?
the internal storage of the component
external storage of the component
permanent storage
all of the above

11. What are arbitrary inputs of components in reacting also known as?
elements
props
keys
ref

12. In MVC, what does React.js act as?
model
controller
View
middleware

13. Identify the smallest building block of React. JS.
props
elements
components
none

14. What is ReactJS mainly used for building?
database
connectivity
user interface
design platform

15. Which of the following functions is used to change the state of the react component?
this.setState()
this.state()
this.setChangeState()
None

16. Among the following which acts as the input of the class-based component?
factory
render
class
props

17. Which keyword is used to create a class inheritance?
Create
Inherits
Extends
This

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18. How many ways of defining your variables in ES6?
1
3
4
5

19. Which of the following are two ways to handle data in react?
services and components
states and props
state and services
state and components

20. ES6 stands for _________.
ECMA 6
ECMAJavaScript 6
ECMAScript 6
EJavaScript 6

Note:

21. Choose the method which refers to the parent class in ReactJS?
this()
super()
inherits()
self()

22. JSX stands for __________.
Javascript XML
JSON XML
JSON
Javascript and AngularJS

23. The function which is called to render HTML to a web page in React?
ReactDOM_render()
render()
render_DOM()
DOM_HTML()

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24. Choose the functionality of setState?
access the previous state before the setState operation
invoke code after the setState operation is done
replace this date completely instead of the default merge action of the above none

25. Which company developed ReactJS?
Apple
Facebook
Google
Twitter

26. React is a ___________.
Javascript framework
Javascript library
both A and B
none

27. Which of the following terms commonly describes react applications?
imperative
integrated
declarative
closed

28. What is React.js?
a) Open-source JavaScript back-end library
b) JavaScript front-end library to create a database
c) Free and open-source JavaScript front-end library
d) None of the mentioned

29. A class is a type of function, but instead of using the keyword function to initiate it, which keyword do we use ?
Constructor
Class
Object
DataObject

30. Which keyword is used to create a class inheritance?
create
inherits
extends
this

31. What would be the output of the following example?
for example,
var Helloword=(props)=>
{
return(
<div>
Hello World 1
</div>
<div>
Hello World 2
</div>
);
}
ReactDOM.render(<Helloworld/>,mountNode)
Hello World 1
Hello World 2
Hello World 1 Hello World 2
Error

33. Which of the following is used in React.js to increase performance? virtual DOM
original DOM
both A and B
none

Frequently Asked React Interview Questions -2

35. Which of the following option is correct in the case of Babel?
Babel is a Compiler.
Babel is a Transpilar.
None of the above.
Both A and B are correct.

36. What changes would appear in the component as soon as the state of the React component is changed?
It will do nothing infact you have to call the render method to render the component again. It will re-render the component.
It can be created again from scratch.
None of the above.

37. What is the use of the create-react-app command in the React.js application?
It is used to update a React app.
It is used to create a new React app.
It is used to install dependencies.
None of the above.

38. What is JSX in React JS?
A syntax extension for JavaScript
A programming language
A data structure in React
A database management system

39. What is the virtual DOM in React JS?
A tool for managing database operations
A tool for optimizing CSS
A tool for optimizing JavaScript code
A representation of the actual DOM in memory

40. What is a prop in React JS?
A way to manage data within a component
A way to pass data from a parent component to a child component
A way to manage routing in a web application
A way to manage user authentication in a web application

41. What is a higher-order component in React JS?
A component that is rendered at the top of the DOM tree
A component that wraps another component and adds functionality
A component that is rendered conditionally based on user input
A component that is used to manage routing in a web application

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42. What is the difference between props and states in React JS?
Props are used to manage data within a component, while the state is used to pass data between components.
Props are immutable, while the state is mutable.
Props are passed from parent to child components, while the state is only accessible within a component.
Props are used for functional components, while the state is used for class components.

43. What is the purpose of the componentDidMount() lifecycle method in React JS?
To update the state of the component
To render a component to the DOM
To perform an action after a component has been rendered to the DOM
To perform an action before a component is rendered to the DOM

44. What is the purpose of the shouldComponentUpdate() lifecycle method in React JS?
a. To update the state of component
b. To render a component to the DOM
c. To determine if a component should be re-rendered
d. To perform an action after a component has been re-rendered

45. What is the purpose of the render() method in React JS?
a. To update the state of component
b. To render a component to the DOM
c. To pass data from a parent component to a child component
d. To manage user authentication in a web application

46. What is the purpose of the React Router library in React JS?
a. To manage state in a React application
b. To handle user input in a React application
c. To add styling to React components
d. To manage routing in a web application built with React

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