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The Top 10 Interview Questions and Answers for React JS

React is an open-source front-end JavaScript toolkit that is used to create user interfaces using user interface components. It is often referred to as React.js or ReactJS. Your front-end engineer interview will likely include advanced questions regarding ReactJS if you are a Java programmer.

FAANG+ organizations frequently test your understanding of Java application tools and microservices, including ReactJS, to share your tool-sharing experiences and grasp of the Java framework. Your success in the technical interview depends on your ability to respond to frequently asked ReactJS advanced interview questions.

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Well-liked Interview Questions and Answers for Advanced ReactJS

Q1. What are the ReactJS framework’s salient characteristics?

Once more, this is a typical ReactJS-related technical interview question.

The following are the key components of the ReactJS framework:

Data binding is made possible by ReactJs, giving developers the ability to control which elements are hidden from users and which are accessible. With this capability, security for the apps they develop is also straightforward.
It is a one-way data stream for ReactJS.
Virtual DOM is used by ReactJs in place of RealDOM.
In React, server-side rendering is mostly used.

Q2. What Kinds Of Lifecycle Techniques Are There In The Mounting Lifecycle Stage?

Display ComponentMount WillMount
Component Did Mount

Q3. In ReactJS, what is an Event?

Events are things that the computer or the user does. In ReactJS, events are actions like keystrokes and clicks. Events in React are written in CamelCase, as opposed to lowercase as in HTML.

Q4: In React, what are Higher Order Components (HOC)?

A function that takes a component and returns a new component is known as a higher-order component (HOC). It is basically a model that is based on React’s compositional architecture. Since they can take any dynamically supplied child component but are unable to alter or duplicate the behavior of their input components, we refer to them as “pure” components.

const EnhancedComponent = higherOrderComponent(WrappedComponent);

HOC has several applications, including the following:

  1. Logic, bootstrap abstraction, and code reuse
  2. Publish Jacking up
  3. Abstracting and manipulating states
  4. manipulation of props

Q5. In what circumstance would you apply React’s useMemo()?

Which developers can utilize Memo() to prevent needless re-rendering, according to your candidates? Or, to put it another way, useMemo() has its uses when a lot of processing is required.

Q6: What makes using super constructors with prop arguments recommended?

Candidates can provide an explanation of them, which the applicants do. to visit this.props within the builder. If your React component has a constructor() function, you can mention it. To invoke the main constructor, use super().

Question 7. What does React’s component-based architecture mean?

Components are the fundamental units of React that are utilized to construct application user interfaces. All individual units become fully reusable and independent of one another because of the component-based system. This indicates that the rendering of the program is straightforward and independent of other UI elements.

Q8. How is an arrow function used in React?

In React, write an expression using an arrow function. makes it simple for users to manually connect components. It’s extremely helpful to use the arrow functions functionality while working with core components. commands and their functions.

render() {
return(
<MyInput onChange={this.handleChange.bind(this) } />
);
}
//Making use of the arrow function
render() {
return(
<MyInput onChange={ (e) => this.handleOnChange(e) } />
);
}

Q9. What is the reason for using ComponentDidMount instead of the constructor or ComponentWillMount when making API calls?

It is best to stay away from adverse consequences. We are unable to delay the Render method’s call until the API returns because it comes right after the WillMount component.

There are no API calls made in the constructor; instead, variables are set there. Use of API calls inside the constructor is not recommended due to potential side effects.

Since the render function is called by code and comes after ComponentWillMount, React expects state to be present. This could not work if any of the state variables are missing, which can occur when using Ajax API calls.

Another explanation is that the extract is called twice: once on the client side and once on the server side when we require server-side rendering for React components. This is done by calling the WillMount component twice. Therefore, this is not the place for us to integrate our APIs.

NOTE: Any modification to the application state that can be seen as the return value outside of the invocation function is considered a side effect. For instance, altering a global variable

Q10. Describe the new React v16.6 features of code splitting and lazy loading.
This shows up frequently in React inquiries, which is not surprising.

React v16.6 added a new feature called Lazy Load, which lets some components load later than usual. This enables us to load elements that load quickly, like text, first and images afterward.

Examine the App.js code that follows. MyComp and ContentComponent are its two constituent parts.

One has a text with the phrase “lorem ipsum,” and the other has a loadable image with the words “unsplash.”

We are now loading MyComp slowly because an image needs to be downloaded. Keep in mind the unique import type, and don’t forget to add the component to Suspense. The alternate component that appears when loading myComp is now included in suspense.

Instantaneous loading of the other ContentComponent will occur.

//App.js
import React, { Component, lazy, Suspense } from "react";
import "./App.css";
import ContentComponent from './components/ContentComponent';
const MyComp = lazy(() => import("./components/myComp"));
class App extends Component {
 render() {
   return (
     <div className="App">
       <header className="App-header">  
         <h1>Lazy Loading Demo</h1>        
          <Suspense fallback={<div>Loading.....</div>}>
            <MyComp />
          </Suspense>
         <ContentComponent />
       </header>
     </div>
   );
 }
}
export default App;
//ContentComponent.js
import React from 'react'
export default function ContentComponent() {
 return (
   <div>
     <p>Lorem Ipsum is simply dummy text of the printing and typesetting industry...</p>
  </div>
 )
}
//myComp.js
import React from "react";
export default () => {
 return <img src="" width="960" height="480" alt="acceronix.com" />;
};

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