React JS Interview Questions and Answers | HopeTutors

1.What are the salient features of React.js?

There are three major characteristics of React.js that has distinguished React from rest of the JavaScript-based programs.

  • Virtual DOM

Instead of the usually implemented real Document Object Model (DOM), React.js uses the simulated version, that is the virtually configured, DOM. The simulation comes with its best advantages.

  • Architecture afar HTML

The fundamental architecture of React can be applied beyond translating the HTML in the browser.

  • Unilateral Data Flow

Properties stream down across to another new component from its parent component. And these properties (or props) are received by the components as a pack of unchangeable values, that is, a JavaScript Object. Every time the value of the properties is altered, the component is permitted to show that particular change.

2.What do you understand by Virtual DOM? Explain its working.

A virtual DOM is a thin and flimsy version of JavaScript object which, in its essence, is merely a duplication of the actual DOM. It is a tree of intersection that catalogues the constituent parts, their characteristics and content as objects and their attributes. The rendering capability of React generates a convergence tree out of the React components. This in turn upgrade this tree in answer to the variations in the data model which is initiated by diverse workings done by the users or by the system application itself.

3.Distinguish between Real and Virtual DOM.

Real DOM

1. It upgrades slowly and gradually.

2. It can directly upgrade HTML.

3. It generates a brand-new DOM if the element upgrades

4. DOM exploitation is very costly.

5. Lot of memory would be wasted.

Virtual DOM

1. It upgrades much faster.

2. It cannot directly overhaul the HTML.

3. Intead, it upgrades the JSX if element also is upgraded.

4. But here DOM exploitation is very cost-effective.

5. No memory wastage is found.

4. What are the differences between React.js and Angular.js?



1. Build-in Structure

2. Furnished Rendering

3. DOM

4. Data Binding

5. Debugging

6. Creator


Merely the View aspect of MVC

Server-side rendering is facilitated.

Uses the simulated virtual DOM

Only the One-way data binding

Debugged in compile -time



The whole part of MVC

Client-side rendering is facilitated.

Uses the actual DOM

Two-way data binding can be done.

Debugged in Run-time.


5. What is Properties?

Properties or commonly known as Props are the components that can only be read. And the key characteristic of which is its unchangeable nature. They are always crossed over across from the parent to the progeny components in all of its application. So a progeny component can never send a property back to its original parent component. This feature assists in keeping the unilateral data flow and are usually used to render the dynamically created data.

6. Define State and its usages in React.js

States are the integral part of React components. States are the original spring of data and should be kept in a simple format. Generally, states are the objects which regulates the components rendering and its conduct in relation to it. They are easily malleable unlike the properties and generate lively and interactive components. They can be accessed through this.state().

7. Distinguish between states and properties.


Stipulations State Properties  (Props)

1. Collect initial value from the originator component.

Yes Yes
2. Source component can alter the value No Yes
3. Set standard values within component Yes Yes
4. Alters within component Yes No
5. Set inceptive value for child components Yes Yes
6. Alters inside child components No


8. What is the Higher Order Components (HOC)?

Higher Order Component is an improved and breakthrough way of using all over again the component logic. Usually, it is a motif that is obtained from React’s configuration structure. HOC is customized components which bounds together another component and includes it. They can concede to any potent progeny component but they will not amend or duplicate any conduct from their input components. So it is suggested that HOC are ‘pure’ or “unadulterated” components.

9. Differentiate between Stateful and Stateless Components in React.

Stateful Component Stateless Component
1. Stores the information about the component’s state alteration in memory phase. 1. Computes the inner state of the components
2. Authorized to alter its state 2. It Does not have the authority to alter the state
3. Constitutes of the knowledge of past, present and potential future alterations in state 3. Constitutes of no pre-knowledge of past, present and potential future state alterations.
4. Stateless components inform them about the needs of the state alterations, then they send forth the properties to them. 4. They get the properties from the Stateful components and regards them as call-back functions.

10. What is Redux and explain it?

Redux is one of the brimming and lively libraries for front-end web development in today’s web development market. It is a foreseeable state container for JavaScript applications and is utilized for the whole applications state monitoring and administration. Applications developed with Redux can be easily tested and can execute in various environments displaying stable behaviour.



September 1, 2018
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