React JS Interview Questions [2020]

Ans: React is a JavaScript library for building awesome user interfaces. If you want to the user for a small project or any big project as you want to React is Flexible. Mainly React can be used to development of single-page or mobile applications. React is maintained by Facebook.

Q2. What is React Component?

Ans: React components are bits of code for any specific purpose component that takes input and returns a React element that describes how a section of the UI (User Interface) should appear.

Q3. What is JSX?

Ans: JSX is a syntax like HTML for declaring the React element and your UI. This is a type of file used by React which utilizes the expressiveness of JavaScript along with HTML template syntax. 

Q4. What is ReactDOM?

Ans: React Dom is a simple package that provides DOM-specific methods that can be used at the top level of a web app to enable an efficient way of managing DOM elements of the web application page.

Q5. Why React is used and what it's advantages?

Ans: Too many reasons to use React Js for building User Interfaces (UI) some are.

• Easy to learn nature
• Simplicity
• High scalability
• Increase performance
• React improves SEO performance
• React use for mobile app development
• React increases efficiency
• React ensures stable code
• React is extremely easy to write UI test cases because the virtual DOM system implemented entirely in JS.

Q6: Does ReactJS use HTML?

Ans. No, ReactJS uses JSX which is similar to HTML.

Q7: When ReactJS released?

Ans: March 2013

Q8: React has something called a state. What is it and how it is used?

Ans: In ReactJS state is a source of Data. they are objects responsible for determining components rendering and behavior. 

Q9: List some features of ReactJS?

Ans:
It’s Adaptability
Free and Open Source
Server-side Communication
Asynchronous Functions & Generators
Flux Library
Destructuring Assignments
Usefulness of JSX

Q10. What is the main difference between createElement and cloneElement?

Ans: Create Element what React uses to create React Elements and cloneElement is basically used to clone an element and pass it new props.

Q11. What is the difference between React Native and React?

Ans: React Native is a framework for mobile app development that compiles to native app components. React Native use to build native mobile applications for Windows, Android, and iOS in JavaScript while we can use ReactJS to build our web components.

Q12 What is React Router?

Ans: React Router use to navigate the application pages when user request for some new page and information. suppose user stand on the home page now he wants to jump on about page so this think is control by react-router.

Q13 Why can’t browsers read JSX?

Ans: We know Browsers can only read JavaScript objects and JSX is not a regular JavaScript object. To enable any browser to read JSX, first, we need to transform the JSX file into a JavaScript object using JSX transformers. To transform JSX to JavaScript object we use Babel and then pass it to the browser.

10. How is React different from Angular?

React vs Angular