React JS Interview Questions

React is a library developed to create reusable user interfaces. Let us understand the key concepts of React by addressing important React JS interview questions.

1. What is React JS?

React JS is a JavaScript library to create web and device user interfaces.
It was started by the Facebook team in 2011.
React encourages developers to create reusable interfaces.
It is assisted by a strong, open-source community.

2. What are Components in React?

Components are an integral part of React. They are the primary units for all technologies centered on React. Components allow developers to decompose a user interface into smaller bits, which can be reused.

3. What is the difference between State and Props?

Props and State are two basic principles you must be familiar with to transfer data across components. The state corresponds to the default database value of a React component. The condition of a component can change over time and can be adjusted by a developer manually.

Props define the configuration of a react component. Props do not have modifications.

4. Explain the lifecycle of React JS Components.

Mounting

These methods are called by generating and adding an instance of a variable in the DOM.

constructor()
getDerivedStateFromProps()
render()
componentDidMount()

Updating

Change in state and props will result in an upgrade. These methods are applied when a component is being re-rendered:

getDerivedStateFromProps()
shouldComponentUpdate()
render()
getSnapshotBeforeUpdate()
componentDidUpdate()

Unmounting

This method is applied when the component is taken out of the DOM.

componentWillUnmount()

5. What is JSX?

JSX is the JavaScript syntax extension. It explains how the user interface looks with React. With JSX, HTML templates can be written in the same file containing JavaScript code.

6. How is React different from Angular?

Angular is a complete framework, while React is a library. React.js uses virtual DOM and one-way data linking while Angular runs on real DOM and two-way data binding. There is also a variation in bundle size and speed.

7. When are keys used in React JS?

In React, keys are used to define individual virtual DOM components.

React can simplify the rendering process using keys so the frame can recycle existing objects loaded to DOM.

8. What are synthetic events in React JS?

SyntheticEvent is an immersive framework over the native event of a browser.

The SyntheticEvent functions much like the browser event framework, the only distinction being that all browsers use the same code.

Eg:

import React, { Component } from 'react';
class ShowAlert extends Component {
showAlert(){
alert(" I'm an alert");
}
render () {
return (
<button onClick= {this.showAlert}> show alert <\button>
);
}
}
export default ShowAlert;

9. What is the use of arrow functions in React JS?

Arrow functions are essential for React operations. It removes bugs. Arrow functions make it easy to predict the action of bugs as they move through callbacks. Therefore the use of these in callbacks prevents bugs.

10. What is Redux?

Redux is a library that supports React and helps developers to create easy-to-test web applications. Redux can be run with React or some other library of JS user interface and provides prepackaged debugging software.

Conclusion

The easiest way to prepare for a technical interview is to prepare the most frequently asked questions.

Practicing the questions covered in this article should help you plan and improve the chances of success in your next technical interview.

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