React.js Interview Questions and Answers

reactjs interview questions

React.js Interview Questions and Answers

ReactJS is an open source JavaScript library built by a group of engineers at Facebook and Instagram for building user interfaces (UI) for web applications and mobile applications. React aims primarily to provide speed, simplicity, and scalability. React also allows us to create reusable UI components. React was first created by Jordan Walke, a software engineer working for Facebook. He was influenced by XHP, an HTML component framework for PHP. It was first deployed on Facebook’s newsfeed in 2011 and later on in 2012. It was open-sourced at JSConf US in May 2013. React first deployed on Facebook’s newsfeed in 2011 and on in 2012.

React Native, which enables native Android, iOS, and UWP development with React, was announced at Facebook’s React.js Conf in February 2015 and open-sourced in March 2015.

On April 18, 2017, Facebook announced React Fiber, a new core algorithm of React framework library for building user interfaces. React Fiber will become the foundation of any future improvements and feature development of the React framework. (Ref wiki says )

Current version is React v 17.0.1 / October 22, 2020.

What is React?

Why ReactJS is used?

How to create “Hello World” in ReactJS?

What is JSX in React?

Why browsers cannot read JSX?

Why React JS?

What is DOM?

What is Virtual Dom in React?

What is React Fiber?

What are the advantages and disadvantages of React?

What is State in ReactJS?

What is Flux?

What were the major problems with MVC framework?

What is Redux in ReactJS?

What are the three principles that Redux follows?

What is the refs and keys used in React?

What is component in ReactJS?

What is PureComponet in ReactJS?

What is the Higher Order Components (HOC) in ReactJS?

What is the lifecycle methods of React components in detail?

What is Props in ReactJS?

What is Router in ReactJS?

What is the difference between Controlled and Uncontrolled components in ReactJS?

What is the difference between createElement and cloneElement in ReactJS?

What is arrow function in ReactJS?

What are synthetic events in React?

Explain the role of Reducer in ReactJS?

Can you define Relay?

Can you explain, how to use https instead of http in create-react-app?

Can you explain React Intl?

What is the difference between mapStateToProps() and mapDispatchToProps()?

Can you explain,how to add multiple middlewares to Redux?

What are the lifecycle methods of components?

How to declare a state object?