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An Overview of ReactJS

ReactJS is JavaScript library for building reusable User interface components. It is a template-based language combined with different functions that support the HTML. This means the result of any React's operation is an HTML code. You can use ReactJS to build all kinds of single page applications.

Development History:

Jordan Walke, a Facebook engineer, developed the React framework in 2011. After using it on Facebook’s news feed, it was implemented on the Instagram network. React became open source in 2013.

Key points about React:

  • Originally developed by Facebook engineers.
  • Implements one-way data flow. Flux keeps data unidirectional.
  • Licensed under Facebook Inc, and documentation is licensed under CC BY 4.0.

Latest Version: React 16.3.0 was released in March 2018

Advantages of React

  • Uses virtual DOM that improves apps performance.
  • Can be used on the client side, server side, and with other frameworks.
  • Component and data patterns improve readability that helps in maintaining larger apps.

Disadvantages of React

  • Support of other technologies required for development.
  • Inline templating and JSX might seem weird to some developers.

If you are looking for a job as a ReactJs developer, we have a vast collection of React Interview Questions & Answers

React js interview questions and answers

Looking for a new job? Do not miss to read our React js interview questions and answers. Whether you are a fresher or an experienced, these questions and answers that can help you to crack your interview.

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

Hete is is an example of JSX:

render(){

      return(

          <div>  <h1> Welcome To Tekslate!!</h1> </div>

     );

 }

Real DOM updates slowly, and is able to directly update the HTML. Whereas, Virtual DOM updates faster but is unable to directly update the HTML.

Real DOM can create a new DOM if element updates, but Virtual DOM only updates the JSX if element updates.

In Real DOM, DOM manipulation is expensive. In Virtual DOM, DOM manipulation is easy.

Too much memory wastage in Real DOM, but there is hardly any memory wastage in Virtual DOM.

Components are the essential elements of a React application's user interface. These elements split up the entire UI into small reusable pieces, and renders these components independent of each other without impacting the rest of the UI.

It is compulsory for each React component to have a render(). If more than one element needs to be rendered, they must be grouped inside one tag such as <form>, <group>,<div>. This function goes back to the single react element which is the presentation of native DOM Component. This function must return the same result every time it is invoked.

Props stand for Properties in React. They are read-only components that must be kept pure. These components are passed down from the parent to the child component throughout the app. A child component cannot send prop back to the parent component. This can help in maintaining the unidirectional data flow and is used to render the dynamically generated data.

States are at the heart of components. They are the source of data and must be kept simple. States determine components’ rendering and behavior. They are mutable and create dynamic and interactive components, and can be accessed via this.state().

Arrow functions, also called ‘fat arrow‘ (=>), are brief syntax for writing the expression. These functions bind the context of the components because auto binding is not available by default in ES6. Arrow functions are useful if you are working with the higher order functions.

Example

                                                

//General way

render() {

return(

<MyInput onChange={this.handleChange.bind(this) } />

);

}

//With Arrow Function

render() {

return(

<MyInput onChange={ (e) => this.handleOnChange(e) } />

);

}

No, React uses JSX that is similar to HTML.

Component lifecycle is an important part of ReactJS. Component lifecycle falls into three categories - property updates, Initialization and Destruction. Lifecycle is a method of managing the state and properties of the components.

Events are the triggered reactions to actions like mouse hover, click, key press, etc.

  • ReactJS depends less on the code whereas AngularJS needs a lot of coding.
  • React packaging is strong as compared to AngularJS.
  • React is equipped with Virtual Dom while Angular has a Regular DOM.
  • ReactJS is all about the components but AngularJS focus on the Models, View and Controllers.
  • AngularJS was developed by Google while ReactJS was developed by Facebook.
Redux is used to handle data in a reliable manner. It performs task accurately and ensures that the data has been controlled. You can also apply filters if only a specific part of data is required.

Flux is an illustration that helps to maintain unidirectional data stream. It also controls construed data unique fragments and makes them interface without creating issues. The configuration of Flux is insipid, and is not specific to applications.

We can utilize Webpack's DefinePlugin strategy to set NODE_ENV to production. This will remove things like propType approval and other notices. It is a good idea to reduce your code because React utilizes Uglify's dead-code end to remove advancement just code and remarks.

The server needs to be regularly monitored for updates. The aim is to check for the presence of new comments. This process is considered as pooling. It checks for the updates almost every 5 seconds. Pooling helps keep an eye on the users and ensure there is no negative information on servers.

If your component has a state or lifecycle method, use Class component. Else, a Functional component.

A component describes what you need to see on the screen. An element is a protest representation of user interfaces. A component is a function that acknowledges input and returns a React component.

JSX gets transpired to createElement and React uses it to make React Elements. cloneElement is used as a part of a request to clone a component and pass new props.

Uncontrolled components maintain their internal state, whereas controlled components do not maintain any internal state. Controlled components can be managed by several methods.

Enclosing the multi-line JSX expression is the best option. Sometimes it becomes necessary to avoid multi-lines in order to perform the task reliably and for getting the expected results.

No. This is because the word Class is an occupied word in the JavaScript. If you use the word Class JSX will get translated to JavaScript.

Yes. This is a complex process, and the best way to do it is by using a spread operator.

React is a JavaScript Library which is used to show content to user and handle user interaction.

In React we divide the front end content into different components so that we can reuse the component when we need them at other place.

Component is a building block of any React app which is made by either JavaScript Function of Class. Ex. Header Component, Footer Component etc.

There are two types of Components.
  • Function Based Component
  • Class Based Component

Basically Function Based Component are the component which are made by JavaScript Functions.It takes props as argument and return JSX.

Example

                                                

Import React from ‘react’;

const ABC = (props ) => {

           <div>

               <h1>Hello World</h1>

          </div>  

}

export default ABC;

Class Based Component is the JavaScript Class. In these Components we extends the JavaScript predefined class into our component.

Example

                                                

Import React,{Component} from ‘react’;

class ABC extends Component {

 render(){

   return(

    <div>

       <h1>Hello World</h1>

</div>

);

}}

export default ABC;

import is used for calling library from its location to your component and uses that library functions in your component.

The Main Difference is of Syntax. Function Based component used props as an argument and is also called stateless component and In class based component we extends all the property of predefined function and used according to our need.

Class Based Component use state and the state is used as props in child component.In Class Based component we can use different lifecycle method of component.

In Stateless component we didn’t define state.State allows your component to change dynamically to the user input. In stateful component we define state for the component.This state is passing as props to other component.

Example

                                                

Stateless Component:

Import React from ‘react’;

 const ABC =() => {

   <div>

 <h1>Hello World</h1>

</div>

 

Stateful Component :

Import React,{Component} from ‘react’;

class ABC extends Component {

state={

    value: ‘’

}

handleChange(event) {

this.setState({

value: event.target.value

});

}

render(){

return(

 <input type=”text” value={this.state.value} onChange={this.handleChange} />

)

}}

1. You have to install node first on your local machine.

2. Open command line and write "npm install -g create-react-app".

3. Then write "create-react-app my-app".

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