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Introduction to ReactJS

ReactJS is an open-source JavaScript library created by Facebook's Jordan Walke to make user interfaces for both web and mobile systems. React was first used in 2011 on Facebook's newsfeed. In 2012, it was used on Instagram, and in 2013 it was made available to the public. React is best for applications that change their data quickly and dynamically. It can show the parts of the UI that are changing without re-rendering the whole page. This makes the user experience much faster. If you are still wondering what ReactJS is all about, let’s go through the introduction to ReactJS and its related aspects.

What is the Use of ReactJS?

JavaScript has become more popular over the past few years. It is used to handle all of an app's views, whether it's a web app or a mobile app. It's also used to reuse user interface (UI) parts. ReactJS lets programmers build web apps that can change data without reloading the page. The best thing about ReactJS is that it is easy to use, and quick. It is also the same as a view in an MVC template. Most of the time, it works like a group of JavaScript libraries or frameworks.

ReactJS's primary goal is to make user interfaces (UI) that make apps load faster. It also uses virtual DOM (JavaScript object), which also helps the ReactJS app run faster. In JavaScript, the virtual DOM is faster than the real DOM. ReactJS can be used on both the server and client-server sides, as well as with other frameworks. It uses data patterns and components to make the code easier to read and make app maintenance easier.

Is React Back-End or Front-End?

Introduction to ReactJS: A Guide for Beginners
Image source: Unsplash

There are numerous debates about whether ReactJS is a framework or a library, and whether it is useful for front-end or back-end web development. React uses Javascript to create interactive user interfaces for single-page apps. The view layer for apps is handled by ReactJS development services, which allow the creation of modular UI components.

ReactJS handles everything that happens on the server side. It has a significant impact on front-end development, with thousands of sites already operating on it. This enables ReactJS developers to create versatile web apps with dynamic data that can work without reloading the page. Even after deployment, ReactJS improves the app by increasing its speed and introducing new features. The most common reasons ReactJS stands out from other front-end development frameworks are speed, flexibility, usability, performance, and reusable components.

What are the Main Features of ReactJS?

Introduction to ReactJS: A Guide for Beginners
Image Source: Unsplash

ReactJS is one of the greatest JavaScript frameworks for web developers, as it plays an important part in the front-end ecosystem. The following are the main features of ReactJS:

JSX (JavaScript Syntax Extension)

JavaScript XML is abbreviated as JSX. It is a syntax extension for JavaScript. ReactJS  uses an XML or HTML-like syntax. The syntax is turned into React Framework JavaScript calls. It expands ES6 to allow HTML-like text to coexist with JavaScript react code. It is not required to use JSX, but it is recommended in ReactJS.

Virtual DOM

DOM stands for Document Object Model. It is the most crucial aspect of web development since it splits the code into modules and then executes it. JavaScript frameworks typically update the entire DOM at once, making the online app slow. However, React makes use of virtual DOM, which is a carbon replica of real DOM. When a web application is modified, the virtual DOM is updated first, and the difference between the real DOM and the virtual DOM is determined. When it discovers the difference, DOM updates the parts that have changed recently, leaving the rest unchanged.

One-way Data Binding

As the name implies, one-way data binding is a one-direction flow. In React, data only goes in one direction, from top to bottom, from parent components to child components. The child component's properties (props) cannot return data to its parent component, but they can communicate with it to change the states based on the inputs. One-way data-binding operates in this manner. Everything remains modular, and as a result, quick. Learn more about how to create components with props and validate prop types in React.

Declarative

ReactJS uses simple JavaScript to enable a component-based approach to develop websites and mobile apps, which has the benefit of cutting development costs. The best features of ReactJS enable web pages and mobile apps to have highly interactive and dynamic user interfaces. When your data changes, it creates basic views for each project state, and React will update and render only the relevant components. When used frequently on websites and apps, the library becomes easier.

React Native

Instead of using web components like React, React Native employs native components as building blocks. To get started with React Native, you'll need to understand basic React concepts like JSX, components, state, and props. Even if you're already familiar with React, you'll need to learn about React Native capabilities like native components.

Component-Based

Everything in React is a web page component separated into individual components to form a view (or UI). Each visual part of the software is encapsulated within a component, which is a self-contained module. Because the component functionality is defined in JavaScript rather than templates, you can give rich data, while keeping the state out of the DOM.

ReactJS components are the building blocks of any React application and are one of the best features in ReactJS, and a single app is typically built of numerous components. A user interface element is essentially the most significant component. React separates the user interface into reusable components that may be processed separately. 

What is JSX, the Basic Syntax Of ReactJS?

JavaScript XML or JSX is a JavaScript syntax extension that allows developers to write HTML directly in React (within JavaScript code). It is simple to generate a template in React using JSX, but it is not a simple template language; instead, it contains all of JavaScript's capabilities.

It is faster than standard JavaScript because it optimises when converting to standard JavaScript. Instead of dividing the markup and logic into different files, React uses components. 

What are the Components Of ReactJS?

Introduction to ReactJS: A Guide for Beginners
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A component is one of React's fundamental elements. In other words, each React application you build will be composed of components. Components make creating user interfaces considerably easier. You can divide a user interface into components and work on them individually before combining them into a parent component, which will be your final UI.

There are two sorts of components: Function components and Class components.

Functional Components

When dealing with React, functional components are some of the most popular components you'll come across. These are nothing more than JavaScript functions. By writing a JavaScript function, we can create a functional component for React. Data may or may not be passed as parameters to these functions. The return value in functional Components is the JSX code to render to the DOM tree.

Class Functions

The class components are more difficult to understand than the functional components. Your program's functional components are oblivious of each other, whereas the class components can collaborate. To create class-based components in React, we can use JavaScript ES6 classes. Information can be sent from one class component to another. The following React example shows a valid class-based component:

{% code-block language="js" %}
class Democomponent extends React.Component
{
    render(){
          return <h1>Welcome Message!</h1>;

{% code-block-end %}

ReactJS components interaction 

Every React app is made up of parts that work together. An important part of the UI architecture is how these parts talk to each other. Component interactions become even more important as apps get bigger and more complicated.

React has several ways to handle this need, and each has its own use cases. Let's start with the easiest way for parents to interact with their children. 

Parent-to-child with props

Properties, often called "props," are the easiest way for components to talk to each other. Props are the arguments that a parent component sends to a child component. They are equivalent to function arguments.

Listing 1: Based on Props

{% code-block language="js" %} function App(){
  return <div>
    <AppChild name="Matt" />
    </div>
}
function AppChild(props){
  return <span>
      My name is {props.name}
    </span>
}
ReactDOM.render(<App />, document.getElementById('app')); {% code-block-end %}

The example that is based on functions shows how the syntax of the functional style is simpler. Here, you can see how this code works.

Child to Parents with Functional Props

If you try to change a child's prop directly, you'll get the following error message in the console:

Uncaught TypeError: Cannot assign to read only property 'foo' of object '#<Object>'

Listing 2: Functional Props

In Listing 2, useState is introduced as a way to manage the state. The point of the functional prop is that when the button is clicked, the App component's function is run. So, the child and the parent are able to talk. 

{% code-block language="js" %}
function App(){
const [name, setName] = React.useState("Matt");
return <div>
<AppChild name={name} onChangeName={()=>{setName("John")}}/>
</div>
} {% code-block-end %}

{% code-block language="js" %}
function AppChild(props){
return <span>
My name is {props.name}
<button onClick={props.onChangeName}>Change Name</button>
</span>
}
ReactDOM.render(<App />, document.getElementById('app'));
{% code-block-end %}

Telling parents about something

A lot of the time, child components need to send arguments up with their events. Adding arguments to the functional prop callback will let you do this. Listing 3 shows how this is taken care of.

Listing 3: Sending arguments to functional props

{% code-block language="js" %}
function App(){
const [name, setName] = React.useState("Matt"); //test
return <div>
<AppChild name={name} onChangeName={(newName)=>{setName(newName)}}/>
</div>
}
function AppChild(props){
return <span>
My name is {props.name}
<button onClick={()=>props.onChangeName("Bill")}>Change Name</button>
</span>
}
ReactDOM.render(<App />, document.getElementById('app'));
{% code-block-end %}

Notice the line onClick="()=>props.onChangeName("Bill")" in Listing 3. Here, we use the arrow syntax to make an anonymous function with the argument we want.It is also simple to pass a variable that is changed by the component, using syntax like onClick="(myVar)=>props.onChange(myVar)".

What are ReactJS Lifecycle Methods? 

Introduction to ReactJS: A Guide for Beginners
Image source: Unsplash

A React Component can go through the four stages listed below:

  • Initialization: This is when the component is made with the given Props and default state. This is done in a Component Class's function Object() { [native code] }.
  • Mounting: This is the rendering stage of the JSX returned by the method itself.
  • Updating: This is the stage when the state of a component is updated and repaints the application.
  • Unmounting: The final step in the component lifecycle is unmounting, which removes the component from the page.

ReactJS Lifecycle Hooks

Hooks are a new feature in React 16.8. They enable the use of state, and other React features without building a class. 

State Hook

The following is the example that helps you understand better

{% code-block language="js" %}
import React, { useState } from 'react';
function Example() {
// Declare a new state variable, which we'll call "count"
const [count, setCount] = useState(0);
return (
<div> {% code-block-end %}

{% code-block language="js" %}
<p>You clicked {count} times</p>
<button onClick={() => setCount(count + 1)}>
Click me
</button>
</div>
);
} {% code-block-end %}

In the above example, useState is a Hook in this case. Between re-renders, React will keep this state. useState returns a pair of values: the current state and a function to update it. This function can be called from an event handler, or from anywhere else. This is comparable, except that setState in a class does not combine the old and new states.

Effect Hooks

The useEffect Effect Hook gives a function component the ability to perform side effects. It accomplishes the same thing as React's componentDidUpdate, componentDidMount, and componentWillUnmount methods, but in a single API.

For example, after React changes the DOM, this component sets the document title:

{% code-block language="js" %}
import React, { useState, useEffect } from 'react';
function Example() {
  const [count, setCount] = useState(0);
 // Similar to componentDidMount and componentDidUpdate:
 useEffect(() => {
   // Update the document title using the browser API
   document.title = `You clicked ${count} times`;
 });
  return (
    <div>
      <p>You clicked {count} times</p>
      <button onClick={() => setCount(count + 1)}>
        Click me
      </button>
    </div>
  );
}
{% code-block-end %}

When you call useEffect, you tell React to run your "effect" function after flushing DOM changes. Effects are declared within the component so that they can access its properties and state. React by default runs the effects after every render, including the first.

Can a Beginner Start with ReactJS? 

Learning React isn't about picking up a new syntax or anything; it's about comprehending how React has chosen to operate with JavaScript. Perhaps a beginner can start with ReactJS, if he/she has:

  • basic knowledge of JavaScript, CSS, and HTML.
  • a basic understanding of ES6 features.
  • an understanding of Let, Arrow Functions, Const, Imports, exports, and classes. 

What do I Need to Know to Start Learning ReactJS? 

Introduction to ReactJS: A Guide for Beginners
Image source: Unsplash

The following are the aspects you need to know when learning ReactJS. It is important to know them before deciding to learn ReactJS:

  • HTML and CSS
  • JSX (Javascript XML) & Babel
  • Fundamentals of Javascript and ES6
  • Package Manager (Node + Npm)
  • Git and CLI (Command Line Interface).

How do I Start Learning ReactJS?

A large developer community supports the React library. This means there are plenty of resources available to help you learn React. Whether you want to learn how to compile a React application and import an image in ReactJS or how to run a ReactJS project in a Local Host, you will find resources that are worth your time. 

So, before you start learning React, consider how you learn best.

Do you enjoy tutorials? Or do you prefer watching videos on the internet? Do you prefer working on interactive projects? Or working through theory before building your own?

By answering these questions upfront, you will be able to focus your search for learning materials. 

Learn ReactJS Online with Microverse

To learn ReactJS, you need to know JS and HTML. You can learn JS and HTML in Level Up at Microverse: The Microverse "Level Up" experience provides a great introduction to software development. It gives you a taste of our collaborative approach at Microverse as you get to learn programming concepts, and practice coding challenges with other applicants from across the world. This practice prepares you to take on the Microverse Coding Challenges needed to apply for the full-time program.

In Level Up, you will get an overview of software development, web development, HTML, CSS, and JavaScript. However, you won't be ready to land a job after that, so we encourage you to apply to our full-time web development program.

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