ReactJS Top 10 Interview Questions

Here are some of the Top 10 ReactJS Interview questions along with answers. If you are a fresher or experienced person looking for a job in ReactJS, these interview questions will help you during your interview.

1. What is React? State some of its key features.

React is a front-end JavaScript library that was developed by Facebook in the year 2013. It is used to develop reusable UI by following the component-based approach. React is used to create complicated and interactive web and mobile user interfaces.

Some of the key features of React are:

  • React makes use of virtual DOM instead of the regular or real DOM.
  • React is used for server-side rendering.
  • React has uni-directional or one-way data flow or data binding.

2. What are the advantages of using React?

Some of the major advantages of using React are:

  • React helps enhance the performance of a web or mobile application.
  • React can be used on the server as well as on the client-side.
  • It used JSX code which increases the code reliability and understandability.
  • React can be integrated with other frameworks like Angular, Meteor, and more.
  • Writing UI test cases for React is very easy

3. Explain Virtual DOM in React?

Virtual DOM is an abstraction of the HTML DOM. It is lightweight and is not connected to the browser-specific implementation details. React provides Virtual DOM for free as the React Elements reside in virtual DOM.

These elements make up the basic nodes of the Virtual DOM tree. Once the React Elements are defined, they can be rendered into the real DOM.

Every time the state of React Component changes, React runs a diffing algorithm. It identifies what changes have been made in the virtual DOM. It then updates the DOM with the results of diff. This process is faster than it would be in real DOM.

4. What is JSX?

JSX stands for JavaScript XML. It is a syntax extension of JavaScript and has all the properties of JavaScript. Any JavaScript expression can be used in JSX by containing it in curly braces.

When it is compiled, JSX elements become regular JavaScript objects. You can use JSX in any statement, loop, to assign values, input arguments, and return functions.

React does not require the use of JSX but it is recommended way of describing the UI in React applications. It makes HTML files easy to understand and also makes the application robust and enhances its performance.

5. What is Redux?

A store in React is a simple JavaScript object. The idea behind Redux is to keep the state of the entire application in a single store, be it the state of the UI like which tab is active currently, or the state of Data like the user profile details.

6. State the difference between Real DOM and Virtual DOM

Real DOM Virtual DOM
It is updated slowly. It updates faster.
It allows a direct update from HTML. It cannot be used to update HTML directly.
It wastes too much memory. Memory consumption is less

7. What is Flux Concept in React?

Facebook widely uses flux architecture concept for developing client-side web applications. It is not a framework or a library. It is simply a new kind of architecture that complements React and the concept of Unidirectional Data Flow.

8. Name the important features of React

Here, are important features of React.

  • Allows you to use 3rd party libraries
  • Time-Saving
  • Faster Development
  • Simplicity and Composable
  • Fully supported by Facebook.
  • Code Stability with One-directional data binding
  • React Components

9. Explain React Router

React Router is a routing library which allows you to add new screen flows to your application, and it also keeps URL in sync with what’s being shown on the page.

10. What are the popular animation package in React ecosystem?

Popular animation package in React ecosystem are:

  • React Motion
  • React Transition Group

11. What is Jest?

Jest is a JavaScript unit testing framework created by Facebook based on Jasmine. It offers automated mock creation and a jsdom environment. It is also used as a testing component.

12. What is dispatcher?

A dispatcher is a central hub of app where you will receive actions and broadcast payload to registered callbacks.

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