Prepare For Every Opportunity: ReactJS Interview Questions & Answers In 2022

Of the many technologies flooding the software industry, ReactJS is slowly and steadily making its way to the list of top tools to master. It is an open-source, front-end JavaScript library used for building User Interfaces. It allows developers to create reusable UI components. The library is essentially created for building fast and interactive user interfaces for both website and mobile applications, and for expertly handling the view layer for the same. Its simplicity, scalability & flexibility urges aspiring developers to pursue it relentlessly.

More than 1,300 developers and over 94,000 sites utilize ReactJS. Some of the most renowned companies that rely on it are Netflix, Airbnb, Instagram, Facebook, PayPal, Uber, & more. Given that the tool is gaining popularity by the hour, the career prospects for front-end developers who possess in-depth knowledge in ReactJS is are quite promising.

Mastering ReactJS is not an impossible task, but it does demand a certain level of dedication and determination. With an ardent passion for the tool and the right opportunities in the industries, you can learn to leverage its true potential and create exceptional websites and apps, beautifying everything that a user sees. But the very first step to a rewarding career in this field is to prepare for the ReactJS interview in a way that nothing takes you by surprise. To help you sail through this challenge, here are some of the key ReactJS interview questions & answers –

Top 15 ReactJS Interview Questions And Answers For Freshers1. What is ReactJS?

First released in March 2013 and developed by Facebook, ReactJS is an open-source JavaScript library that makes it easier for developers to build intuitive user interfaces.

2. What is JSX?

JSX stands for JavaScript XML. It is a type of file used by React which utilizes the expressiveness of JavaScript along with HTML-like template syntax. This makes the HTML file easy to understand. This file makes applications robust and boosts their performance.

3. Why can’t browsers read JSX?

Browsers can only read JavaScript objects but JSX is not a regular JavaScript object. To enable a browser to read JSX, one has to first transform the JSX file into a JavaScript object using JSX transformers like Babel and then pass it to the browser.

4. What are the three key features of ReactJS?

It is fully supported by Facebook

It allows one to use 3rd party libraries

It ensures code stability with one-directional data binding

5. What are the advantages of ReactJS?

It is compatible to be used on the client as well as server-side

Writing UI test cases is very easy

It can be easily integrated with other frameworks like Meteor, Angular, etc

The code’s readability is enhanced, thanks to JSX

6. What are the limitations or drawbacks?

Integrating React with the MVC framework like Rails requires complex configuration.

React is just a library, not a full-blown framework

Its library is very large and takes time to understand

7. What is Virtual DOM?

A virtual DOM is a lightweight JavaScript object which originally is just a copy of the real DOM. It is a node tree that lists the elements, their attributes, and content as Objects and their properties. ReactJS’ render function creates a node tree out of the React components. It then updates this tree in response to the mutations in the data model which is caused by various actions done by the user or by the system.

8. What are the differences between Real DOM and Virtual DOM?

Real DOM is updated slowly. Virtual DOM updates faster.

Real DOM, unlike Virtual DOM, allows a direct update from HTML.

Real DOM takes up too much memory while Virtual DOM does not.

9. What does the term ‘stateless components’ mean?

Stateless components are pure functions that render DOM-based solely on the properties provided to them.

10. What is React Router?

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

11. What does the term ‘Redux’ mean in ReactJS?

Redux is a library used for front-end development. It is a state container for JavaScript applications that should be used for the applications state management. You can test and run an application developed with Redux in different environments.

12. What is a State in ReactJS?

The State is an updatable structure that holds the data and information about the component. It may be changed over the lifetime of the component in response to user action or system events. It is the heart of the react component which determines the behavior of the component and how it will render. It must be kept as simple as possible.

13. What is Flux Concept?

Facebook widely uses flux architecture concepts 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.

14. What is the popular animation package in React ecosystem?

React Motion

React Transition Group

15. What is meant by callback function? What is its purpose?

A callback function should be called when setState has finished, and the component is re-rendered. As the setState is asynchronous, which is why it takes in a second callback function.

Top 15 ReactJS Interview Questions And Answers For Experienced Professionals1. What are high-order components?

A higher-order component also shortly known as HOC is an advanced technique for reusing component logic. It is not a part of the React API, but they are a pattern that emerges from React’s compositional nature.

2. What is the arrow function in ReactJS?

Arrow functions are more of a brief syntax for writing the function expression. They are also called ‘fat arrow‘ (=>) the functions.

3. How can you update the State of a component?

We can update the State of a component using this.setState() method. This method does not always replace the State immediately. Instead, it only adds changes to the original State.

4. What is an event in ReactJS?

In React, events are the triggered reactions to specific actions like mouse hover, mouse click, keypress, etc.

5. What are Props?

Props stand for "Properties" in React. They are read-only inputs to components. Props are an object which stores the value of attributes of a tag and works similar to the HTML attributes.

6. What are synthetic events in React?

Synthetic events are the objects which act as a cross-browser wrapper around the browser’s native event. They combine the behavior of different browsers into one API. This is done to make sure that the events show consistent properties across different browsers.

7. What are refs in ReactJS?

Refs are attributes that help to store a reference to a particular ReactJS element or component, which will be returned by the components render configuration function. They are used to return references to a particular element or component returned by render(). They come in handy when we need DOM measurements or to add methods to the components.

8. What are pure components in ReactJS?

Pure components help with enhancing the simplicity of the code and the performance of the application. They are the fastest components that can replace any component with only a render().

9. What is an action in Redux?

Actions can send data between the Store and the software application. It is a function that returns an action object. The action-type and the action data are always stored in the action object. All information retrieved by the Store is produced by the actions.

10. What are error boundaries?

Error boundaries help you to catch JavaScript errors anywhere in the child components. They are most used to log the error and show a fallback UI.

11. What is the StrictMode?

StrictMode allows you to run checks and warnings for react components. It runs only on development build. It helps you to highlight the issues without rendering any visible UI.

12. What is Babel in ReactJS?

Babel, is a JavaScript compiler that converts the latest JavaScript like ES6, ES7 into plain old ES5 JavaScript that most browsers understand.

13. What are ReactJS hooks?

React hooks allows you to use State, and other React features without writing a class.

14. How can we do server-side rendering in React?

We can use reaction serve to do the server-side rendering.

15. What is the main difference between React JS and React Native?

ReactJS is a front-end open-source JavaScript library used for building UIs.React Native is an open-source framework that allows developers to use React on platforms like Android and iOS.

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