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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.
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.
React was released in March 2013.
No, React uses JSX.
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:
There are five predefined prototypes in React JS. These are listed below:
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.
React provides some extraordinary and customizable advantages. Below some of the principal advantages:
Despite all the advantages, React has some limitations too. A developer has to encounter the following limitations:
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.
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.
There are some notable differences between State and Props. Some of the major aspects are highlighted below:
The dispatcher is a hub of applications where actions are received. It allows a developer to broadcast payload to registered callbacks.
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.
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.
Some of the major reasons behind using JSX files are illustrated below:
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.
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.
Some significant distinctions are visible between real DOM and virtual DOM. Below are the major differences:
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.
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.
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.
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.
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.
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.
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.
The method of handling State in an application is called reduction.
An element can be shared in the parsing using the State.
Props are immutable. So it’s impossible to update any value of props.
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.
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>
);
}
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.
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.
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.
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.
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;
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.
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.
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.
HOC is used for accomplishing various tasks. Some of them are given below:
The important methods of react-dom packages are-
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.
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.
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.
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.
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} />;
}}
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
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;
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>
);
}
}
Below the usefulness of Ref:
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.
A developer can execute runtime type checking for Props through the prop-types library. It works similarly to an object in web applications.
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 = { };
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.
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.
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:
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.
Below are the different phases of React component’s lifecycle:
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.
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.
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.
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.
The key differences between controlled and uncontrolled components are described below:
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>
);
}
});
There are some notable distinctions between stateless and stateful components. Some of them are given below:
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;
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
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.
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:
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.
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:
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>
);
}
}
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.
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>
React Router gives immense advantages to a developer. Some of the standout facilities are given below:
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.
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>
)
The major differences between these two routing approaches are given below:
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.
Below are the important features of Redux workflow:
Redux consists of the following three core components.
Redux basically conforms to the following three principles:
In this principle, the entire application is stored inside a single store. The single store easily changes, debugs, and inspects the application.
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.
The pure functions are applied to specify the transformation of actions and to return a new State.
The notable problems with the MVC framework are below:
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.
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.
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.
The most visible differences between Redux and Flux are given below:
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
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>
}
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.
There are four ways to style the React components such as inline styling, CSS module, CSS style sheet, and styled-components.
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.
The important React lifecycle methods are below:
componentDidMount() getlnitialState() componentWillMount() componentWillUnmount() componentWillReceiveProps() shouldComponentUpdate() componentWillUpdate() componentDidUpdate()
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
A developer can dispatch the data in-store based on actions. In this case, action stores only the parent component.
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.
A super keyword is useful to call the functions. Besides, it helps a developer to get access to the object’s parent.
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.
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