100+ React JS Interview Questions

Share on facebook
Share on twitter
Share on linkedin
Share on pinterest
Share on reddit
Share on whatsapp
Share on email
Reading Time: 20 minutes
If you’re a full-fledged React JS developer and dreaming of working at a well-established software company, you may sharpen your interview knowledge as soon as possible. You will be asked several questions corresponding to your acquired skillset during the interview session. It’s obvious that you have to give a quick response to strengthen your seat over others.   There are some common but important questions that are kept into account in order to recruit a new candidate. You need to master these to level up your skills and understanding to a significant margin. What are the most-asked React JS interview questions?  You can scroll down here to discover everything and achieve the required knowledge to fulfill your dream.

Table of Contents

What is the best tutorial for React JS?

There are plenty of resources online to learn React JS. Professional programmers are sharing their views and expertise via websites and Youtube to help others. As a beginner, you may look for the Edureka E-learning platform to get your hands dirty on React. This site offers both video and descriptive tutorials on their official website and Youtube channel. The FreeCodeCamp can also be a preferred option to be a master in React JS.

Top 100+ React JS Interview Questions


What is React?

React is an open-source JavaScript library. It’s developed by Facebook in 2011.  The front-end developers use it to build reusable UI components. It’s comprehensively used for developing interactive view layers of web and mobile applications. Whatsapp, Instagram, and many more renowned websites used in React to build a single-page application. It’s efficient, flexible, and declarative.


When was React released first?

React was released in March 2013.


Does React use HTML?

No, React uses JSX.


What are the key features of React?

React comprises some user-friendly and effective features. It has been gaining the utmost popularity among the developers for past few years because of the following features:

  • Components
  • JSX
  • Virtual DOM
  • One-way data binding 
  • Simplicity
  • Performance

What are the most important prototypes in React JS?

There are five predefined prototypes in React JS. These are listed below:

  • String
  • Element
  • Number
  • Object
  • Array

What do you understand from “In React, everything is a component”?

React follows a component-based approach to building up applications. The components are the blocks of a definite application.  A particular application is divided into reusable, independent, and small pieces of code through the components. Without affecting the user interface of an application, React renders each of these components uniquely. That’s why it’s said that everything is a component in React.


What are the core advantages of React?

React provides some extraordinary and customizable advantages. Below some of the principal advantages:

  • Reusable components
  • Easy to apply 
  • Easy to learn
  • Enhanced performance
  • SEO friendly
  • Scalable and customizable 
  • Scope of testing the codes
  • Features some handy tools
  • Perfect for creating dynamic web applications

What are the limitations of React?

Despite all the advantages, React has some limitations too. A developer has to encounter the following limitations:

  • View part issue
  • Very poor documentation
  • JSX barrier
  • The high pace of development

What is a state in React?

In React, the state is a structure that can be easily updated.  It particularly contains data and information of the component. In response to a system event, the state may be changed over the lifetime of the component. The state specifies the behavior of the component. It’s the core segment of the React component that seems simple.


What about the Props in React?

Props refer to the properties in React. They are a type of object which holds the value of attributes of a tag. Besides, Props work as ready-only inputs to components similar to the HTML attributes. By managing a ready-made way to pass data from the parent to the child components, it keeps the application dynamic and interactive.  The working procedures of props are similar to the function arguments.  A developer can’t modify the props from inside the component as they are immutable.  But these can be used to render dynamic data in the render method.


What is the difference between State and Props?

There are some notable differences between State and Props. Some of the major aspects are highlighted below:

State:

  • The state is mutable and asynchronous 
  • A developer can’t access state by child components
  • The state primarily contains the information of the components
  • The state is unable to make components reusable
  • Rendering dynamic changes with the components are easy with State
  • A stateless component never holds state
  • The state is internal and handled by the components

Props:

  • Props are immutable and read-only
  • A developer can access props with child components
  • Props have the ability to make components reusable
  • Props make communication between components
  • A developer can transfer data from as an argument with props
  • Props consist of all the stateless components
  • Props are external and controlled by components

What is a dispatcher?

The dispatcher is a hub of applications where actions are received. It allows a developer to broadcast payload to registered callbacks.


What is JSX in React?

JSX is a React extension. It allows the developers to write JavaScript code like HTML code. The JSX can elevate the performance of the React application to a great extent. It also makes the HTML files easy to grasp and provides the developer to write XML-like syntax. The JSX file features names, attributes, and children to make the React applications potent.


What is the yield catchphrase?

Yield catchphrase is a crucial method of React JS. It’s applied to ensure necessary delay in application. Besides, it’s utilized to resume generator work.


Why JSX is used comprehensively in a React application?

Some of the major reasons behind using JSX files are illustrated below:

  • The JSX is faster than JavaScript as it performs optimization during the translating period of code
  • It’s capable to create templates, type-safe, and causes very few errors
  • It uses components to contain markup and logic in the same file instead of separating technologies

Why browsers can’t read JSX?

JSX is not an original JavaScript object. But the browsers can only read the JavaScript objects. That’s why browsers become unable to understand JSX directly. A developer needs to transform the JSX file into a JavaScript object to let the browsers read it.


What is virtual DOM?

A virtual DOM is an in-memory representation of real DOM. It’s basically a JavaScript object which acts as a mediator between the render function and the displayed elements.  A virtual DOM also lists the elements, content, and attributes as objects. 


What are the differences between real DOM and virtual DOM?

Some significant distinctions are visible between real DOM and virtual DOM.  Below are the major differences:

Real DOM:

  • Real DOM becomes updated at a slow pace
  • It’s updatable directly from HTML
  • It needs huge memory and wastes most of space

Virtual DOM:

  • Virtual DOM needs less time to be updated
  • It doesn’t allow a direct update from HTML
  • It needs less memory 

What are Babel and Webpack in React?

In simple words, Babel is a compiler that converts the latest JavaScript into the old ES5. It makes the code understandable to most of the browsers.  And a Webpack is a module builder which runs in the course of the development process. 


What is the purpose of render() in React?

A render function is an essential component of React library. It’s used to return the HTML code which a developer wants to show in a particular component. The render function allows the developers to render multiple HTML elements at a time using the group tag.


What are the most-used animation packages in React eco-system?

The most-used and popular animation packages are React motion and React transition group. Both of the packages play a significant role to reach the development goal overnight. 


What is the strict mode?

StictMode is a specialized method for running checks and warning for react components. Without passing any visible user interface, it can pinpoint the potential and ongoing issues. It only runs on the development build.


What is React Context and React portal?

React context is a simple method of transforming data with the development tree of react components. It’s essential to pass and share data across the application. It combines various react components. On the other hand, React portal is used to render children into a DOM node. 


What is the arrow function?

An arrow function is a standard function assorted in the ES6 standard.  It works without the necessity of binding any event to ‘this’. There is no need for any calling function to work with the arrow function.  The scope of ‘this’ is global in an arrow function.


What is a callback function?

A callback function is an integral element of React. It’s called when the component is re-rendered and setState get finished.  The setState gets taken in a second callback function as it’s asynchronous.


What do you know about reduction?

The method of handling State in an application is called reduction.


How do share elements in the parsing?

An element can be shared in the parsing using the State.


Is it possible to update the values of props?

Props are immutable. So it’s impossible to update any value of props.


What is an event in React?

An event is an action. It triggers as a result of the user action like click, mouse-over, mouse-out, pressing a key, resizing windows, loading a web page, etc.  The event handling system is the same as the DOM elements handling.  The process of event handling is known as Synthetic Event in React. 


What are the synthetic events in React?

In React, a synthetic event is an object which acts as a cross-browser wrapper. It makes a combination of the behavior of different browser’s native events into one API. 

function ActionLink() {  
function handleClick(e) {  
 e.preventDefault();  
console.log(Successful');  
 }  
return (  
<a href="#" onClick={handleClick}>  
Click here   
</a>  
 );  
}  

What is ReactDOMServer?

ReactDOMServer is typically used on node servers. It’s an object that can be used in both browser and server environments. A developer can render components to static markup using this object. The renderToStaticMarkup() and renderToString() are the most used methods.


What is the significance of keys in React?

In React, a key is a unique identifier that identifies the changed, updated, or deleted items from the lists. It’s essential for creating dynamic components and changing the schema of lists. Besides, a key determines a collection of components to speed up the performance of an application.


What are lists in React?

Lists are the sequential data. In React, lists are used to showcase data by keeping track. A developer can create a list similarly he or she does in JavaScript. The elements inside the lists can be traversed using the map() function.


What do you know about Jest?

Jest is developed by Facebook. It’s a popular JavaScript unit testing framework that provides automated mock creation and jsdom environment. A developer can test components by using Jest.


How to create forms in React?

Creating forms in React is easy and straightforward. A developer can develop forms alike to the HTML forms. In this case, a JavaScript function operates the submission of gathered information. The state property of the component is updated through the setState() function. A form can contain several types of data including text fields, checkboxes, buttons, radio buttons, and so on to collect the required information from the users.

import React, { Component } from 'react';    
class App extends React.Component {  
constructor(props) {  
super(props);  
this.state = {value: ''};  
this.handleChange = this.handleChange.bind(this);  
this.handleSubmit = this.handleSubmit.bind(this);  
}  
handleChange(event) {  
this.setState({value: event.target.value});  
}  
handleSubmit(event) {  
alert(successful: ' + this.state.value);  
 event.preventDefault();  
 }  
render() {  
return (  
<form onSubmit={this.handleSubmit}>  
<h1>Controlled Form Example</h1>  
<label>  
 Name:  
<input type="text" value={this.state.value} onChange={this.handleChange} />  
</label>  
<input type="submit" value="Submit" />  
</form>  
);  
}  
}  
export default App;  

What are pure components?

Pure components conform to shouldComponentUpdate() React lifecycle method. The method returns a Boolean value to decide the re-rendering of the components. It facilitates the state and props to re-render the necessary components. The pure components are effective to increase the simplicity and performance of the application. 


What do you understand about the Higher-Order Components (HOC)?

HOC is an updated approach to reusing specific component logic. It’s similar to a function that accepts and returns a new component. To illustrate, it’s a function that accepts a function as an argument. 


What is the use of ‘key’ and children prop?

The Key is a unique identity. It ensures each list element a stable property. As for the children’s props, they are comprehensively used to pass components as properties. A developer can access both at ease.


What is the use of HOC?

HOC is used for accomplishing various tasks. Some of them are given below:

  • State manipulation 
  • Code reusability 
  • Props manipulation
  • Render highjacking 

What are the important methods of react-dom package?

The important methods of react-dom packages are-

  • findDOMNode()
  • createPortal()
  • render()
  • hydrate()
  • unmountComponentAtNode()

What are fragments?

Fragments are new forms of components that return multiple elements. Without including an extra node to the document object model, it allows a developer to combine a list of multiple children.


Why are fragments better than container divs?

The DOM inspector is hardly cluttered in fragments. Besides, fragments are faster and use less memory. Some CSS styling suits well to the fragments to make the desired layout. That’s why fragments are better.


What are the terms of reconciliation and restructuring?

The actual DOM gets updated in an application automatically if Props change. This process is acknowledged as reconciliation. On the other hand, restructuring is an extraction method of an array. It helps a developer to separate each array object into different variables.


What are refs in React?

In React, refs used for references. A developer can store a reference to the particular DOM nodes through this handy attribute.  In addition, it’s helpful for accessing React DOM nodes or React elements.  It’s essential to alter the value of the child components and interact with them. 


How to create refs?

React.creatRef() function is used to create refs. The function is assigned to an instance property and referenced throughout the components. Below are the codes:

class MyComponent extends React.Component {
constructor(props) {
super(props);
this.callRef = React.createRef();
}
render() {
return <div ref={this.callRef} />;
}}

What is create-react-app?

The create-react app is used to build single-page React applications. Its configuration is like Webpack or Bebel. The setup needs less time. A developer needs to run a single command to start a new project. The single-line command includes React, flow syntax support, prefixed CSS, and ES6.  It also attaches a fast and interactive unit test runner with built-in support. To wan about the common mistakes, it includes a live development server. A built-in script is incorporated to unite CSS, JS, and images. The code is below:

$ npx create-react-app my-app

What are Forward Refs?

The Forward Refs is an additional feature to pass a ref through a component towards a child component. React.forwardRef() method is used to activate it. It’s comprehensively used in reusable component libraries and higher-order components.

import React, { Component } from ‘react’;
import { render } from ‘react-dom’;
const TextInput = React.forwardRef((props, ref) => (
<input type=”text” placeholder = “Hello” ref{ref}/>
));

const inputRef = React.createRef();
class CustomTextInput extends React.Components {
handleSubmit = e = > {
e.preventDefault();
console .log(inputRef.current.value);
};
render(){
return (
<div>
<form onSubmit={e=> this.handleSubmit€}>
<TextInput ref={inputRef} />
  <button>Submit</button>  
</form>  
</div>    
  );  
  }  
export default App;  

How to modularize code in React?

In React, code can be modularized using the export and import properties. A developer can write the components individually in several files. 

export default class ChildComponent extends React.Component {
    render() {
        return(           
<div>        
<h1>Child </h1>
           </div>
        );
    }
}

Why Ref used in React?

Below the usefulness of Ref:

  • Ref is used to returning a certain reference to the element
  • It can be used for the purposes of a callback function
  • It can trigger imperative animations
  • It’s necessary for managing focus, media playback, and text selection
  • It’s used to integrate third-party DOM libraries

What is the best option between findDOMNode() and callback refs?

The callback refs offer better control where refs are either set or unset. On the contrary, findDOMNode() resists quick improvements and development in React in the future. That’s why the callback refs are preferred options over findDOMNode() API.


What is the purpose of using ‘prototypes library?

A developer can execute runtime type checking for Props through the prop-types library.  It works similarly to an object in web applications. 


How to apply validation on props in React?

Props validation function is inevitable to make code clean and readable. A developer can avoid future issues and bugs apply this function. PropTypes property is used to catch bugs by validating data types. In React, App.propTypes method is used to apply validation on props.  When an invalid data type is passed, the warning appears on the JavaScript console.  

class App extends React.Component {
render() {}
}
Component.propTypes = { };

What is Relay and Presentation segment in React?

Relay is a dynamic JavaScript framework. It’s used to ensure data layer and client-server communication in web applications.  Relay basically works with React view layer. On the other hand, a presentation segment helps a developer to render HTML considering the capacity of the segment.


Why you use a capital letter to start component names?

In React, a component name that starts with lower case shows an error as an unrecognized tag.  It’s because the lower case names are considered as HTML tags in JSX. Hence it’s necessary to start components names with a capital letter.


How to write comments in React?

Comments are essential to describe a definite segment of code. A developer has to use both single-line and multi-line comments to give a brief explanation of the functionality of a specific section. The outline of leaving a comment below:

{/* comments +/}

Do you know the difference between element and component?

The key differences between elements and components are given below:

Element:

  • An element is immutable and a plain JavaScript object
  • It describes the component state and DOM node
  • It contains the type, properties, and child elements of components
  • Methods are not applicable to elements

Component:

  • A component is mutable and the core building block of React application
  • It contains state and props to have access to the React lifecycle method
  • It basically accepts an input and returns a React element
  • Methods are applicable to components 

What is the term polling in React?

The process of checking novel comments and monitoring server updates with respect to time is called pooling.  Pooling makes sure the absence of unexpected information on the servers by taking a sharp eye on the users.  In every five seconds, pooling checks the update.


What are the different phases of React component’s lifecycle?

Below are the different phases of React component’s lifecycle:

Mounting phase:

In the mounting phase, the instance of a specific component is created or developed. Besides, the created component is added to the document object module in this phase.

Unmounting phase:

It’s contrary to the mounting stage. In this stage, the created component is destroyed and removed from the document object module.  It’s the latest phase of the React lifecycle.

Initial phase:

It’s the starting phase of the React lifecycle. The components begin moving forward to the DOM in this phase. A component holds initial State and default Props as a constructor.

Updating phase:

This phase ensures the display of the latest version of the components. When a prop or stage change occurs, this stage potentially updates and re-render. It’s a repeatable phase.


What are the differences between controlled and uncontrolled components?

The key differences between controlled and uncontrolled components are described below:

Controlled components:

  • A controlled component allows validation control
  • It accepts the current value as a prop
  • It never maintains the internal state
  • It offers better control over the form elements
  • Data is controlled by the parent element 

Uncontrolled component:

  • An uncontrolled component doesn’t allow validation control
  • It accepts a current value as refs 
  • It can maintain the internal state
  • It offers limited control over the form elements
  • Data is controlled by the DOM

How to create an event in React?

The method of creating an event in React is below:

class Display extends React.Component({      
show(msgEvent) {  
},     
render() {        
 
return (              
<div onClick={this.show}>Click here</div>   
);      
 }  
});  

What are the differences between stateful and stateless components?

There are some notable distinctions between stateless and stateful components. Some of them are given below:

Stateless component:

  • The stateless component is easy to understand and very simple
  • A stateless component can’t be reused 
  • It’s acknowledged as a functional component
  • The lifecycle method of React does not appeal to it
  • It never contains the past, current, and future stage changes

Stateful component:

  • A stateful component is complex and reusable 
  • It’s regarded as a class component in React
  • I can hold or manage states 
  • All lifecycle methods of React are applicable to it
  • It contains the past, current, and future changes of states

How to update the State of a component?

This.setState() method is used to update the state of a component. It predominantly changes the original State and updates the user interface in response to event handlers. 

Code:

import React, { Component } from 'react';  
import PropTypes from 'prop-types';  
  
class App extends React.Component {  
   constructor() {  
      super();        
      this.state = {  
          msg: "Welcome"  
      };      
      this.updateSetState = this.updateSetState.bind(this);  
   }  
   updateSetState() {  
       this.setState({  
          msg:"ReactJS"  
       });  
   }  
   render() {  
      return (  
         <div>  
             <h1>{this.state.msg}</h1>  
             <button onClick = {this.updateSetState}>SET STATE</button>  
         </div>  
      );  
   }  
}  
export default App;  

How to embed multiple components into one?

Multiple components can be embedded into one in the following way:

import React from 'react'  
class App extends React.Component {  
   render (){  
      return (  
         <h1>Hello</h1>  
      )  
   }  
}  
   
class Example extends React.Component {  
   render (){  
      return (  
         <h1>Hi</h1>  
      )  
   }  
}  

export default App 


What are React hooks?

React hooks are essential to use various React features and states without writing a single class.  It’s a unique method of reusing stateful logic without making any change to the hierarchy of components. A developer can test everything individually through the React hooks.


Do you know the difference between React Native and React JS?

React Native and React JS both are JavaScript libraries. But there are differences in terms of usability, performance, and scalability. Below are the key differences:

React JS:

  • React JS is a front-end JavaScript library used for developing web applications
  • It uses React-router for triggering web pages and can be applied on all platforms
  • It uses HTML tags, JavaScript libraries, and CSS
  • The virtual DOM renders the browser code in React

React Native:

  • React Native comes with the built-in animation libraries 
  • It’s used for developing mobile applications 
  • It uses API to render code and features a built-in navigator library 
  • It doesn’t appeal to all platforms and never use HTML tags

How virtual DOM works?

Generally, virtual DOM works in three phases. Firstly, the entire UI is re-rendered in virtual DOM representations of data changes in the React App. Then a significant difference between the previous DOM representation and the new DOM comes about and is calculated. After measuring the DOM, the real DOM becomes updated with the changes.


What is the difference between React and Angular JS?

React and Angular JS is the popular and most-used JavaScript libraries. They are different in terms of use, compatibility, scalability, and performance. Some of the core distinctive characteristics are given below:

React JS:

  • React JS is developed with JSX language
  • It’s an open-source JavaScript library 
  • It works with virtual DOM and client-side application 
  • It features unit-testing and Uni-directional data-binding 
  • It’s fast and easy to understand 

Node JS:

  • Node Js is developed with JavaScript and HTML
  • It’s an open-source MVC framework
  • It works with regular DOM and server-side application
  • It features unit and integration testing and Bi-directional data-binding
  • It’s slow and hard to realize 

How ES6 syntax of React is differs from ES5?

The difference between ES6 and ES5 syntax in terms of components and functions is provided below:

 ES5:

var MyComponent = React.createClass({  
    render: function() {  
        return(  
          <h3>Hello</h3>  
        );  
    }  
});  

ES6:

class MyComponent extends React.Component {  
    render() {  
        return(  
          <h3>Hello</h3>  
        );  
    }  
}  

What is React router?

React Router is an advanced, user-friendly, and standard routing library system. It’s built on top of React and used to create Routing. A developer can apply React Router Package in the React application. It also needed to determine multiple routes in the app can get the synchronous URL on the browser. Developing single-page web applications and maintaining behaviors of applications seem easier with it.


What is the necessity of a Router in React?

React Router is essential to display various views in a single-page web application. It allows creating, defining, and redirecting multiple routes. By leading a user to a unique view, it plays a crucial role in the application.

Code:

<switch>  
      <h1>React Router</h1>  
      <Route path="/home" component={Home} />  
      <Route path="/about us" component={About} />  
      <Route path="/contact us" component={Contact} />  
</switch>  

What are the advantages of React Router?

React Router gives immense advantages to a developer. Some of the standout facilities are given below:

  • It helps to specify every component in <Route>
  • It works with the Switch method to render components
  • A single child element is enough for the router
  • Links can be used to trigger internal links in the app like the anchor tag
  • It supports the compact size of React application 
  • It’s divided into three packages 

Why switch keyword used in React Router v4?

In React Router v4, the <switch> keyword is used to render specific components. It also displays only a single Route to all the rendered routes. If the path matches it works, otherwise it returns an error.


Why you get a warning in React Router?

It causes if the Routes wrapped in a <switch> or <div> block.  The example is given below:

render((  
  <Router>  
    <Route {/* ... */} />  
    <Route {/* ... */} />  
  </Router>  
)  
should be
render(  
  <Router>  
    <Switch>  
      <Route {/* ... */} />  
      <Route {/* ... */} />  
    </Switch>  
  </Router>  
)  

What is the difference between React Router and conventional routing?

The major differences between these two routing approaches are given below:

React routing:

  • A single HTML page is needed in React Routing
  • It only changes the <BrowserRouter> attribute
  • A user can’t navigate different pages for each view

Conventional Routing:

  • Every view contains a new file in conventional routing
  • The corresponding HTML pages are received through the HTTP request
  • A user can navigate different pages for each view

What is Redux?

Redux used comprehensively in React for developing the user interface. It’s an open-source JavaScript library that is easy to run in different environments. A developer can manage the application state through it. By applying Redux, a developer can easily read data from a store, dispatch actions, and check the changed data at ease. It follows a unidirectional data flow model to manage the state.


What are the significant features of Redux workflow?

Below are the important features of Redux workflow:

  • Reset: it resets the State of the Store
  • Sweep: It removes all the disabled actions
  • Revert: It helps to call back the last committed State
  • Commit: It makes the current state to the initial State

What are the main components of Redux?

Redux consists of the following three core components. 

  • Store: The entire State of a particular application placed in Store.
  • Action: Action determines what’s happening for a certain moment
  • Reducer: Reducer specifies the change of State 

What principles does Redux follow?

Redux basically conforms to the following three principles:

Single source of truth:

In this principle, the entire application is stored inside a single store. The single store easily changes, debugs, and inspects the application.

The State is read-only:

According to this principle, neither the views nor the network callbacks can directly write to the State. It needs to emit an action to do so.

Changes are made with pure functions:

The pure functions are applied to specify the transformation of actions and to return a new State.


What problems have to face with the MVC framework?

The notable problems with the MVC framework are below:

  • It seems hard to debug the application 
  • It causes massive memory wastage
  • The application becomes inefficient and slow 
  • DOM manipulation is very expensive 

What the role of the Reducer?

Reducer is a pure function that reads the payloads from the actions and updates the Storage. In addition, it returns a new state without executing any further work.


What about the Flux concept?

Flux is used to build the client-side web application in React. It backs React to keep data updated and create the view section. It maintains the concept of a unidirectional data flow model. But it’s neither an acknowledged framework nor a library.


What is the importance of Store in Redux?

A Store is a heart object of Redux which contains the State of application. It offers several methods to dispatch actions, accesses the State, and register listeners.  In addition, A Store is efficient for handling the data processing and performing several actions to change State.


What are the differences between Redux and Flux?

The most visible differences between Redux and Flux are given below:

Redux:

  • Redux is used to manage application State
  • It’s immutable and an open-source JavaScript library 
  • It features a single store but doesn’t contain a dispatcher concept

Flux:

  • Flux is a kind of architecture that used to contain State and change logic
  • It’s mutable and follows the concept of a unidirectional data flow model
  • It features multiple stores and a single dispatcher

How to access the Redux store from outside a component?

In order to access the Redux store from outside a component, it’s necessary to import the Store from the module.  The code is below:

store = createStore(myReducer)  
export default store  

How to use styles in React?

To use style attribute in React applications, a developer needs to write the following code:

const divStyle = {  
  color: 'red',  
  backgroundimage: 'url(' + imgUrl + ')'  
};  
  
function HelloWorldComponent() {  
  return <div style={divStyle}>Hello World!</div>  
}  

What are styled-components?

Styled components are the successor CSS modules that used styling a definite application. The styled-components provide automatic critical CSS, simple dynamic styling, and easier deletion of CSS advantage. They leave no class name bugs and offer effortless maintenance.


How many approaches can you style the React component?

There are four ways to style the React components such as inline styling, CSS module, CSS style sheet, and styled-components.


How does CSS module styling work in React?

CSS module can style the React components without permission. It stores all the animation and class names automatically to style the components.  The components which import it can apply it; but it can’t be applied to the other components.


What are the major lifecycle methods of React components?

The important React lifecycle methods are below:

componentDidMount()
getlnitialState()
componentWillMount()
componentWillUnmount()
componentWillReceiveProps()
shouldComponentUpdate()
componentWillUpdate()
componentDidUpdate()

Why setState() is asynchronous?

SetState() offers a better UI experience and performance without leaving the browser unresponsive. Besides, it creates a pending state transition and returns the existing value as a batch. The synchronous operation can never gain such performance. Hence setState() actions are undoubtedly asynchronous. 


How does JSX resist injection attacks?

React DOM converts the components into a string before rendering them. Besides, it avoids any embedded value in JSX not allowing inject anything. That is how JSX prevents cross-site-scripting or injection attacks.


Is it necessary to define a constructor for React component?

In React, components can be manipulated and implemented without the use of a constructor. This is because there is no need to initialize state and bind methods. So it’s no mandatory to define a constructor.


What are React Decorators?

React Decorators combine the higher-order components and functions. A developer can take an existing class component or function to ensure the utmost capabilities of an application through the React decorator. They never cause any mess with codebase in order to ensure modification. 


What are the advantages of Flux?

The applications of Flux feature easy to test, updated, and manageable components. There causes no data affection and compatibility issues. Besides, the Flux applications are highly scalable. That’s why Flux seems always beneficial to the developers.


How to increase the performance of a React application?

In order to enhance the performance of a React application, a developer needs to keep the DOM updating. Besides, he or she should try to reduce the re-rendering of components and optimizing the size of the final JavaScript file. This can be done by using PureComponent or componentShouldUpdate libraries. 


What are selectors?

Selectors are a kind of special function. They are used to perform transformation, calculation, mapping, filtering, and so on in an application. Typically, selectors accept state and return a portion of it to return the desired results.  Selectors can be called without changing the state and specifying a view.


What is the windowing technique?

The windowing technique is helpful for rendering a small subset of rows within a little time. It can reduce working time and enhance the rendering process exponentially. The windowing libraries offer various reusable components to make sure the effortless display of grids, lists, and tabular data.


What are the benefits of flexbox?

Flexbox handles the layout of CSS by reducing the need for different grid libraries. It offers optimal flexibility and control to the design. In addition, it eliminates the use of floats to place blocks on the layout.  In a word, Flexbox solves a lot of problems in a web application.


How to structure a complete React application?

The structure of an application is based on a module or feature. The user interface schema plays the leading role in this case.  Having combined UI and domain logic is essential to structure a business and data-driven application. The atomic structure needs proper planning and a modeling diagram.


What are the best ways to debug an issue in React?

There are some industry-standard debugging tools to ensure the efficiency of a particular application. A developer can reach out for either Linters or Debuggers to perform such a crucial part. 


What is the suspense component in React?

The suspense component wraps the custom components in order to make a connection with React. It facilitates data rendering and enhances the overall performance of an application. But it has no similarity with Redux or react-async in terms of working.


How to dispatch the data in-store?

A developer can dispatch the data in-store based on actions. In this case, action stores only the parent component. 


What is DOM diffing in React?

The new VDOM tree and the old VDOM tree are different in various aspects. A developer can detect the core distinctions of those by following a heuristic O(n) algorithms. And this process is called “diffing”. It helps a developer to get rid of unnecessary changes. 


What is the necessity of a super keyword in React?

A super keyword is useful to call the functions. Besides, it helps a developer to get access to the object’s parent. 


Final words

A React developer is in high demand. Software companies have been recruiting a massive amount of React developers over the years. If you’re hoping to get hired at your dreamed company, you may get ready completely. Along with mastering your coding skills, you need to become efficient in answering the interview questions. 

If you can give an instant response to most of the queries, the chance of getting appointed will increase to a great extent. Hence you might keep focused on the most-asked interview questions. However, as you’ve already found a broad range of questions with appropriate answers, you can keep practicing them to solidify your understanding and skill.

Do you find yourself getting stuck in SEO or design?

What are you looking for? We can help solve your problems, in seo, web design, content writing and shopify store. Let us know about the issue and we will fix it!