Home Interview Questions Top 20+ React Interview Questions With Answers in PDF 2019

Top 20+ React Interview Questions With Answers in PDF 2019

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Top 20+ React Interview Questions With Answers

Top 20+ React Interview Questions With Answers: Here are the top interview questions of React. Be prepared for the interview. You can download the entire questions in a pdf format. so guys All the best for your interview.

Q1: What is React? What are some of its standouts?

Answer: React is a frontend JavaScript library. It was developed by Facebook in 2011. It enhances application performance while allowing for working on both client-side and server-side.

Writing UI test cases is simple with React, which is also easy to integrate with Angular, Meteor, and other popular JS frameworks. Here are some of the major standouts of React:

  • Excellent for developing complex and interactive web and mobile UI
  • Follows the component-based approach and helps in building reusable UI components
  • Features one of the largest community support
  • Makes use of the virtual DOM instead of the real DOM

Q2: React has something called a state. What is it and how it is used?

Answer: States are the source of data for React components. In other words, they are objects responsible for determining components behavior and rendering. As such, they must be kept as simple as possible.

Accessible by means of this.state(), state is mutable and create dynamic and interactive components. Use of a state can be visualized by the following code snippet:

class App extends React.Component { 
constructor() {
super();
this.state={
foo: 'bar'
} }

Q3: Why do we use render() in React?

Answer: In React, each component must have a render() function. It returns a single React element, which is, in fact, the representation of the native DOM component.

When there is a need for more than one HTML element to be rendered, we group them in one enclosing tag, which can be <div>, <form>, <group>, or some other tag. There is a need for the render() function to return the same result each time it is invoked i.e. it needs to be kept pure.

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Q4: Explain major differences between the ES5 and ES6 syntax with relevant examples.

Answer: The syntax has witnessed a great change from ES5 to ES6. Important differences among the two releases of ECMAScript are:

  • Require vs. Import – The require used in ES5 is now replaced with import.var React = require(‘react’); //is now replaced with
    import React from ‘react’; //in ES6
  • Export vs. Exports – Instead of exports, now export is used.export default Component; // replaces
    module.exports = Component; // in ES6
  • Component and Function – The use of component and function has also changed from ES5 to ES6.
    In ES5:
var MyComponent = React.createClass({ 
render: function() {
return <h3>Hello World!</h3> ;
}
});
In ES6:
class MyComponent extends React.Component {
render() {
return <h3>Hello World!</h3> ;
}
}
  • Props – Rules for using props has also changed from ES5 to ES6

In ES5:

var App = React.createClass({ 
propTypes: {
name: React.PropTypes.string },
render: function() {
return <h3>Hello, {this.props.name}!</h3> ;
}
});
In ES6:
class App extends React.Component {
render() {
return <h3>Hello, {this.props.name}!</h3> ;
} }
  • State – Using state has also been tweaked for ES6.
In ES5: 
var App = React.createClass({
getInitialState: function() {
return { name: 'world' };
},
render: function() {
return <h3>Hello, {this.state.name}!</h3> ;
}
});
In ES6:
class App extends React.Component {
constructor() {
super();
this.state = { name: 'world' };
}
render() {
return <h3>Hello, {this.state.name}!</h3> ;
} }

Q5: Explain the Virtual DOM and its working.

Answer: Top 20+ React Interview Questions With Answers: A virtual DOM is a lightweight JS object. It is simply a copy of the real DOM. A virtual DOM is a node tree that lists various elements, their attributes, and content as objects and their properties.

The render() function in React is responsible for creating a node tree from the React components. This tree is then updated in response to the mutations resulting in the data model due to various actions made by the user or the system.

The Virtual DOM operates in three simple steps:

  • Step 1 – The entire UI is re-rendered in Virtual DOM representation as soon as there are some underlying data changes.
  • Step 2 – Now, the difference between the previous DOM representation and the new one (resulted from underlying data changes) is calculated.
  • Step 3 – After the calculations are successfully carried out, the real DOM is updated in line with only the things that actually underwent changes.

Q6. What is the difference between ReactJs and AngularJs?

Answer:
Both ReactJs and AngularJs are a very powerful and diverse approach for a front-end web application. It supports all small medium and large enterprise application. One side the ReactJs application SEO friendly, simple and easy to understand and the other side Angular Js applications are easy to develop and supports a different form of testing.

Q7. How flux is different from Redux?

Answer:
Flux is a container for application state and logic while Redux is a container for javascript apps.

Q8. What do you mean a functional component in React?

Answer:
Functional component is those components which returns react elements as an element.

Q9. What do you mean by reacting routing?

Answer:
In React Routing only single HTML page will be involved.

Q10. What is the component of Redux?

Answer:
Top 20+ React Interview Questions With Answers: Action, Reducer, Store, View are the component of Redux.

Q11How does the React Router differ from conventional routing?

  • Changes in the URL – A HTTP request is sent to a server for receiving a corresponding HTML page in conventional routing. React routing necessitates only for a change in the History attribute.
  • Navigation – In conventional routing, the user actually navigates across different web pages for each individual view. In React routing, however, the users feel like they are navigating across distinct webpages while in actuality they aren’t.
  • Pages – Whereas in React routing only a single HTML page is involved, each view corresponds to a new file in conventional routing.

Q12How does the state differ from props in React?

  • Changes inside child components are possible with props but not with state
  • Changes inside component aren’t possible with props but with state
  • Props allow for parent component to change value, state doesn’t

Q13How will you distinguish Redux from Flux?

  • Components – React components subscribe to the store in flux whereas in redux, container components utilize connect
  • Dispatcher – There is no dispatcher in redux. On the other hand, flux has a singleton dispatcher
  • Number of Stores – While flux has several stores, there is only a single store for redux
  • State – It is mutable for flux but immutable for redux
  • Store – In flux, the store contains state as well as change logic. Contrary to this, the store in redux is separate from the change logic
  • Store Type – All stores in flux are disconnected and flat. This is not the case with redux, where there is a single store with hierarchical reducers

Q14How would you create a form in React?

Answer: React forms are identical to HTML forms. However, the state is contained in the state property of the component in React and is updateable only via the setState() method.

Therefore, the elements in a React form can’t directly update their state. Their submission is handled by a JS function, which has full access to the data entered into the form by a user.

Following code demonstrates creating a form in React:

handleSubmit(event) { 
alert('A name was submitted: ' + this.state.value); event.preventDefault();
}
render() {
return (
<form onSubmit={this.handleSubmit}>
<label>
Name: <input type="text" value={this.state.value} onChange={this.handleSubmit} />
</label>
<input type="submit" value="Submit" /> </form>
); }

Q15. Which Company developed the React and when the first release got to happen?

Answer:
Facebook is the developer of React and the first release was happen in March 2013.

Q16. What is the stable version of ReactJs?

Answer:
Version:15.5

Q17. What is the basic difference between pros and state?

Answer:
The basic difference is: State is mutable and Pros are immutable.

Let us move to the next ReactJs Interview Questions

Q18. When you will use the class component over a functional component?

Answer:
Top 20+ React Interview Questions With Answers: When your component carrying a state or lifecycle then we will use the Class component.

Q19. How we share the data between components in React?

Answer:
By using State, Prop we share the data.

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Q20: What are the advantages of using Redux?

  • Better Code Organization – Redux is precise in terms of how the code needs to be organized. This results in a consistent code workable for any development team
  • Developer Tools – Allow developers to track each and everything, ranging from actions to state changes, happening in the application in real time
  • Easy Testing – Redux code is mainly composed of functions that are isolated, pure, and small. Hence, testing is much easy and simple
  • Large-scale Community – Redux is backed by a mammoth community. It contributes to an ever-growing and refined library and ready-to-use applications
  • Maintainability – Thanks to a predictable outcome and strict structure, the code is easier to maintain.
  • Output Predictability – There is no confusion about syncing the current state with actions as well as other parts of the application as there is only a single source of truth, which is the store
  • Serverside Rendering – There is a need of only passing the store created on the server-side to the client-side. In addition to this being useful for initial render, it also offers a better user experience because it optimizes the application performance

Q21What do you understand by Props in React?

Answer: Top 20+ React Interview Questions With Answers: Props is a contraction for Properties in React. These read-only components need to be kept immutable i.e. pure. Throughout the application, props are passed down from the parent components to the child components.

In order to maintain the unidirectional data flow, a child component is restricted from sending a prop back to its parent component. This also helps in rendering the dynamically generated data.

Q22Where would you put AJAX calls in your React code?

Answer: It is possible to use any AJAX library with React, such as Axios, jQuery AJAX, as well as the inbuilt browser window.fetch.

Data with AJAX calls need to be added to the componentDidMount() lifecycle method. By doing this, it is possible to use the setState() method for updating component as soon as the data is retrieved.

Top 20+ React Interview Questions With Answers in PDF

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