React is a JavaScript library for building user interfaces. It's widely used in web development, particularly for creating reusable components and optimizing rendering performance. Companies like Facebook, Instagram, Airbnb, and Netflix rely on React for their applications.

Last updated on:- 1st June 2023

What is the virtual DOM in React JS ?

A lightweight version of the actual DOM

A separate DOM that runs on the server

A concept that allows React to efficiently update and render components

A tool for debugging React applications

The virtual DOM is a concept in React JS that provides a lightweight representation of the actual DOM. It allows React to efficiently update and render components by performing a differential update, minimizing actual DOM manipulations.

What is state in React JS ?

A built-in React JS component

A static data store for global variables

A JavaScript object used to store and manage component data

A lifecycle method in React JS

State in React JS refers to a JavaScript object that holds component-specific data. It allows components to manage and update their own data independently, enabling dynamic rendering and interactivity.

What is the purpose of React Router in React JS ?

To handle HTTP requests and server-side routing

To manage state and data flow in React components

To facilitate client-side routing in a single-page application

To provide a testing framework for React JS applications

React Router is a library in React JS that enables client-side routing in a single-page application. It allows for dynamic rendering of components based on the URL, providing a seamless navigation experience.

Which keyword is used to define a class component in React JS?

function

component

class

render

In React JS, a class component is defined using the `class` keyword, followed by the component name and the `extends` keyword to inherit from the `React.Component` class.

What is the purpose of React Hooks in React JS ?

To style React components using CSS-in-JS

To manage asynchronous operations and API calls

To create reusable component logic and manage component state

To provide a mechanism for internationalization in React JS

React Hooks in React JS provide a way to create reusable component logic and manage component state without writing class components. Hooks such as useState and useEffect enable functional components to have state and lifecycle functionality.

What is the file extension for React JS components?

.rct

.jsx

.react

.html

React JS components typically use the file extension `.jsx` to differentiate them from regular JavaScript files. This extension is used to indicate that the file contains JSX code.

What is the purpose of React DevTools ?

To profile and optimize React JS applications

To provide a visual editor for designing React components

To enable real-time collaboration among React JS developers

To generate documentation for React JS code

React DevTools is a browser extension and development tool that allows developers to inspect, profile, and debug React JS applications. It helps identify performance.

What is a functional component in React JS ?

A component written using the functional programming paradigm

A component that can be reused across multiple projects

A component that does not have a state or lifecycle methods

A component that renders a single HTML element

A functional component in React JS is a JavaScript function that returns JSX to describe the UI. It does not have its own state or lifecycle methods, making it simpler and lightweight.

Which method is used to render a React component into the DOM ?

renderComponent

mount

append

render

The `render` method is used to render a React component into the DOM. It is called on the ReactDOM object and takes two arguments: the component to render and the target DOM element where the component should be rendered.

10.

What is the purpose of React Fragments ?

To group multiple React components together

To enable server-side rendering in React applications

To improve performance by reducing unnecessary re-rendering

To provide a mechanism for styling React components

React Fragments allow grouping multiple React components together without introducing additional DOM elements. They are useful when multiple components need to be rendered together, especially in cases where a wrapping element is not desirable.

11.

Which package is used for state management in React JS?

Redux

Axios

React Router

Lodash

Redux is a popular package used for state management in React JS applications. It provides a centralized state store and allows for predictable state updates using actions and reducers.

12.

What is the purpose of PropTypes in React JS ?

To define the types of component props

To handle HTTP requests and API calls

To manage component state and lifecycle methods

To create reusable UI components

PropTypes in React JS is a type-checking mechanism used to define the types and structure of component props. It helps catch bugs and provides documentation for component usage.

13.

What is the purpose of React Context ?

To handle form validation in React applications

To manage global state accessible by all components

To enable client-side routing in a React application

To optimize rendering performance in React components

React Context provides a way to share data across the component tree without passing props manually at each level. It allows for the creation of a global state that can be accessed by all components within the context.

14.

Which prop is used to pass data from a parent component to a child component in React JS?

state

props

data

value

Data can be passed from a parent component to a child component in React JS using props. Props are read-only and provide a way to pass information down the component tree.

15.

Which method is used to update the state of a component in React JS?

setState

updateState

changeState

modifyState

The `setState` method is used to update the state of a component in React JS. It takes an object or a function as an argument and merges it with the current state, triggering a re-render of the component.

16.

What is the purpose of React.memo() in React JS ?

To memoize expensive computations in React components

To create higher-order components (HOCs)

To handle form submissions in React applications

To create reusable presentational components

React.memo() is a higher-order component in React JS. It is used to memoize the result of a component's render and avoid unnecessary re-rendering. It can improve performance by optimizing component rendering.

17.

What is JSX in React JS?

A JavaScript syntax extension for creating React elements

A separate programming language used in React applications

A library for managing asynchronous operations in React components

A testing framework for React JS applications

JSX is a syntax extension in React JS that allows you to write HTML-like code in JavaScript. It enables the creation of React elements and components with a familiar HTML-like syntax.

18.

What is the purpose of the useEffect hook in React JS?

To handle user input and form submissions

To perform side effects in functional components

To manage component state in class components

To optimize rendering performance in React components

The useEffect hook in React JS allows you to perform side effects, such as data fetching, subscriptions, or manual DOM manipulation, in functional components. It replaces lifecycle methods like componentDidMount, componentDidUpdate, and componentWillUnmount.

19.

Which hook is used to perform side effects in functional components in React JS?

useState

useEffect

useReducer

useContext

The `useEffect` hook in React JS is used to perform side effects in functional components. It allows you to perform operations such as data fetching, subscriptions, or manually changing the DOM after the component has rendered.

20.

What is the purpose of the useCallback hook in React JS ?

To manage global state accessible by all components

To create reusable component logic and manage component state

To optimize rendering performance by memoizing functions

To handle client-server communication in React applications

The useCallback hook in React JS is used to optimize rendering performance by memoizing functions. It returns a memoized version of the callback function, preventing unnecessary re-creation of the function on each re-render.

21.

Which method is used to handle user input changes in React JS?

onChange

onClick

onSubmit

onMouseOver

The `onChange` method is used to handle user input changes in React JS. It is commonly used with input elements, such as text fields or checkboxes, to capture and respond to user input.

22.

What is the purpose of the useRef hook in React JS ?

To handle form validation and user input

To manage component state and lifecycle methods

To optimize rendering performance by memoizing components

To access mutable values or DOM elements in functional components

The useRef hook in React JS is used to access mutable values or DOM elements in functional components. It returns a mutable ref object that persists across component re-renders and can hold any mutable value.

23.

Which operator is used to render a list of elements in React JS?

for loop

if statement

map

switch case

The `map` operator is commonly used in React JS to render a list of elements. It allows you to iterate over an array and return a new array of elements based on the provided logic.

24.

What is the purpose of the useContext hook in React JS ?

To handle form validation and user input

To manage global state accessible by all components

To optimize rendering performance by memoizing components

To enable client-side routing in a React application

25.

What is the purpose of the useState hook in React JS ?

To handle asynchronous operations and API calls

To manage component state in class components

To optimize rendering performance in React components

To create reusable component logic and manage component state

The useState hook in React JS allows functional components to have state. It returns a stateful value and a function to update it, enabling the management of component state within functional components.

26.

What is the purpose of the useMemo hook in React JS ?

To handle user input and form submissions

To optimize rendering performance by memoizing values

To manage component state and lifecycle methods

To facilitate client-side routing in a React application

The useMemo hook in React JS is used to memoize the result of a function and cache its return value. It helps optimize rendering performance by preventing unnecessary re-computation of values on each re-render.

27.

What is the purpose of the useReducer hook in React JS ?

To manage global state accessible by all components

To handle client-server communication in React applications

To create reusable component logic and manage component state

To optimize rendering performance by memoizing components

The useReducer hook in React JS is used to manage complex state logic within functional components. It returns a state value and a dispatch function, allowing for the creation of reusable component logic to manage state changes.

28.

What is the purpose of the componentDidCatch lifecycle method in React JS ?

To handle HTTP requests and server-side routing

To manage component state in class components

To catch and handle errors in React component trees

To optimize rendering performance in React components

The componentDidCatch lifecycle method in React JS is used to catch and handle errors that occur in any component within its component tree. It provides a way to gracefully handle errors and display fallback UI when errors occur during rendering.

29.

What is the purpose of the getDerivedStateFromProps lifecycle method in React JS ?

To handle user input and form submissions

To optimize rendering performance in React components

To manage global state accessible by all components

To update component state based on changes in props

The getDerivedStateFromProps lifecycle method in React JS is used to update component state based on changes in props. It provides a way to synchronize component state with prop changes and is invoked before rendering when new props are received.

30.

Which lifecycle method is invoked immediately after a component is inserted into the DOM?

componentDidMount

componentWillUnmount

componentDidUpdate

componentWillUpdate

The `componentDidMount` lifecycle method is invoked immediately after a component is inserted into the DOM. It is commonly used to perform initialization tasks, such as data fetching or setting up event listeners.

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React JS

React is a JavaScript library for building user interfaces. It's widely used in web development, particularly for creating reusable components and optimizing rendering performance. Companies like Facebook, Instagram, Airbnb, and Netflix rely on React for their applications.

The virtual DOM is a concept in React JS that provides a lightweight representation of the actual DOM. It allows React to efficiently update and render components by performing a differential update, minimizing actual DOM manipulations.

State in React JS refers to a JavaScript object that holds component-specific data. It allows components to manage and update their own data independently, enabling dynamic rendering and interactivity.

React Router is a library in React JS that enables client-side routing in a single-page application. It allows for dynamic rendering of components based on the URL, providing a seamless navigation experience.

In React JS, a class component is defined using the `class` keyword, followed by the component name and the `extends` keyword to inherit from the `React.Component` class.

React Hooks in React JS provide a way to create reusable component logic and manage component state without writing class components. Hooks such as useState and useEffect enable functional components to have state and lifecycle functionality.

React JS components typically use the file extension `.jsx` to differentiate them from regular JavaScript files. This extension is used to indicate that the file contains JSX code.

React DevTools is a browser extension and development tool that allows developers to inspect, profile, and debug React JS applications. It helps identify performance.

A functional component in React JS is a JavaScript function that returns JSX to describe the UI. It does not have its own state or lifecycle methods, making it simpler and lightweight.

The `render` method is used to render a React component into the DOM. It is called on the ReactDOM object and takes two arguments: the component to render and the target DOM element where the component should be rendered.

React Fragments allow grouping multiple React components together without introducing additional DOM elements. They are useful when multiple components need to be rendered together, especially in cases where a wrapping element is not desirable.

Redux is a popular package used for state management in React JS applications. It provides a centralized state store and allows for predictable state updates using actions and reducers.

PropTypes in React JS is a type-checking mechanism used to define the types and structure of component props. It helps catch bugs and provides documentation for component usage.

React Context provides a way to share data across the component tree without passing props manually at each level. It allows for the creation of a global state that can be accessed by all components within the context.

Data can be passed from a parent component to a child component in React JS using props. Props are read-only and provide a way to pass information down the component tree.

The `setState` method is used to update the state of a component in React JS. It takes an object or a function as an argument and merges it with the current state, triggering a re-render of the component.

React.memo() is a higher-order component in React JS. It is used to memoize the result of a component's render and avoid unnecessary re-rendering. It can improve performance by optimizing component rendering.

JSX is a syntax extension in React JS that allows you to write HTML-like code in JavaScript. It enables the creation of React elements and components with a familiar HTML-like syntax.

The useEffect hook in React JS allows you to perform side effects, such as data fetching, subscriptions, or manual DOM manipulation, in functional components. It replaces lifecycle methods like componentDidMount, componentDidUpdate, and componentWillUnmount.

The `useEffect` hook in React JS is used to perform side effects in functional components. It allows you to perform operations such as data fetching, subscriptions, or manually changing the DOM after the component has rendered.

The useCallback hook in React JS is used to optimize rendering performance by memoizing functions. It returns a memoized version of the callback function, preventing unnecessary re-creation of the function on each re-render.

The `onChange` method is used to handle user input changes in React JS. It is commonly used with input elements, such as text fields or checkboxes, to capture and respond to user input.

The useRef hook in React JS is used to access mutable values or DOM elements in functional components. It returns a mutable ref object that persists across component re-renders and can hold any mutable value.

The `map` operator is commonly used in React JS to render a list of elements. It allows you to iterate over an array and return a new array of elements based on the provided logic.

The useState hook in React JS allows functional components to have state. It returns a stateful value and a function to update it, enabling the management of component state within functional components.

The useMemo hook in React JS is used to memoize the result of a function and cache its return value. It helps optimize rendering performance by preventing unnecessary re-computation of values on each re-render.

The useReducer hook in React JS is used to manage complex state logic within functional components. It returns a state value and a dispatch function, allowing for the creation of reusable component logic to manage state changes.

The componentDidCatch lifecycle method in React JS is used to catch and handle errors that occur in any component within its component tree. It provides a way to gracefully handle errors and display fallback UI when errors occur during rendering.

The getDerivedStateFromProps lifecycle method in React JS is used to update component state based on changes in props. It provides a way to synchronize component state with prop changes and is invoked before rendering when new props are received.

The `componentDidMount` lifecycle method is invoked immediately after a component is inserted into the DOM. It is commonly used to perform initialization tasks, such as data fetching or setting up event listeners.