What Is ReactJS, and What Can It Be Used For?

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If you want to create fast, dynamic user interfaces for your web applications, then you need to learn how to use ReactJS.

React is a client-side JavaScript library, which means it runs on the client/user’s machine in the browser as opposed to running on a server.

It was created in 2011 by the tech giant, Facebook. The React library is used to build dynamic user interfaces and operates by separating aspects of the user interface into what is known as "components".

In this tutorial article, you’ll learn everything you need to know about React and its components.

What Is ReactJS?

React (also known as ReactJS) is an open-source JavaScript library, which is often erroneously called a framework. This is because React is a direct competitor of top JavaScript frameworks such as AngularJS and VueJS.

React is a library because it doesn’t have a routing mechanism among other framework-specific features. However, there are tools such as the react-router that can be installed and used with the library to achieve framework functionality.

React is more closely related to frameworks such as Angular/Vue than it is to other libraries in the language such as jQuery.

What Are the Benefits of Using ReactJS?

Many developers use React for a plethora of different reasons; some use it because of its speed and performance, and others use it simply because of its popularity. However, there are three major benefits of using the framework that all developers can appreciate.

It allows you to build your interface using what is referred to as "reusable components" which have state and data.

It uses a JavaScript syntax extension (JSX) that allows the user to write dynamic HTML.

It uses a Virtual Document Object Model (VDOM), which allows the developer to update specific sections of a webpage without having to reload the page.

What Are ReactJS Components?

React treats each section of a user interface as a component. Components have states, methods, and functionality.

They allow a developer to separate a user interface into specific sections, which are easily combined to create complex user interfaces. Therefore, if you want to create a customer manager, one component of the user interface can be dedicated to adding a new customer, while another component of the same user interface can be dedicated to displaying the customer list.

RELATED:An Intro To Web Components And Component-Based Architecture

In its simplest form, a component is a JavaScript class or function. They take input values which are called ‘props’ and return specific aspects of a user interface in the form of React elements. For some developers, defining a component as a function is simpler than defining it as a class; however, using either method achieves the same output in React.

Creating a Component with a Function Example

function Customer() { return ( <div> <h3>Paul Wilson</h3> <ul> <li>Phone: 222-222-2222</li> <li>Email: [email protected]</li> <li>Balance: $0.00</li> </ul> </div> ); } export default Customer;

Creating a Component With a Class Example

import React from 'react'; class Customer extends React.Component { render() { return ( <div> <h3>Paul Wilson</h3> <ul> <li>Phone: 222-222-2222</li> <li>Email: [email protected]</li> <li>Balance: $0.00</li> </ul> </div> ); } } export default Customer;

As you can see from the examples above, there’s a lot more happening when you create a component using a class. The first important thing to note is that you have to use the render() function when creating a class component.

As you may know, you can’t return directly from a class; therefore, the render() function helps to accomplish this.

The main reason why a developer might choose to use a class over a function is that a class has a state, but thanks to the introduction of hooks, React functions can now also have a state.

What Is JavaScript Syntax Extension?

The JavaScript syntax extension (JSX) is the React element returned by a component. It's a description of what a specific section/component should look like in the user interface. Its appearance is similar to HTML, but in reality, it's JavaScript.

JSX Example

<div> <h3>Paul Wilson</h3> <ul> <li>Phone: 222-222-2222</li> <li>Email: [email protected]</li> <li>Balance: $0.00</li> </ul> </div>

The JSX example above has been pulled from the customer component. The code appears to be HTML, but it's JSX. Though the differences between the two aren’t very apparent from the example above, there are some clear differences. For example, in HTML you use the class property to group similar elements, but in JSX you use the className property.

What Is the Virtual DOM?

The Virtual Document Object Module (VDOM) is a copy of the real DOM. Generally, when an update is made to the real DOM, the user interface, which is altered, will need to be refreshed to display the changes. However, with a Virtual DOM, the changes to a user interface are instantaneous. The state of the Virtual DOM is then used to update the real DOM in a process known as "reconciliation".

Exploring the React Project Files

When a new React project is created, several different files and folders are automatically generated. One of these folders is labeled public. The public folder contains the only HTML file in the React boilerplate, which is entitled index.html.

The index.html file has a <div> tag with a root id, which is important because this is where the main React component is rendered (which is the name given to the process of transforming your react components into DOM nodes that can be displayed in a browser).

However, the rendering process takes place in another file—index.js—where the React Application root file, which is the App.js file is rendered then passed to the index.html file.

From the index.html file, you can change the title of your web application; however, every other adjustment to the React application (including the creation of a new component) is made from another folder—the src folder. The src folder contains the index.js and the App.js files.

The App.js file is the root react component and it's responsible for what is initially presented in your web browser on the first React application launch. The App.js file contains a function called App that returns JSX. Learn more about the React boilerplate and how to install the react app here.

Creating a Component

When creating a component there’re two things you need to know. The first and most important is that the newly created component will never be displayed in your user interface unless it's imported and utilized in the App component—the App.js file.

The second thing is that it's common practice to begin every component file name with a capital letter. As stated above, a component can be created using either a function or a class. However, React is moving away from class components and is now mainly using functions.

Creating a New Component Example

function Customer() { return ( <div> <h3>Paul Wilson</h3> <ul> <li>Phone: 222-222-2222</li> <li>Email: [email protected]</li> <li>Balance: $0.00</li> </ul> </div> ); } export default Customer;

The code above creates a new customer component and exports the function so that the customer component can be imported by the App component.

Using the App Component Example

import Customer from './components/Customer'; function App() { return ( <div> <h1>Customer Manager</h1> <Customer/> </div> ); } export default App;

As you can see in the example above, the app component imports the customer component and arranges it in the order that it should appear in the user interface (which in this case is after the customer manager label). The App component is then exported, and imported by the index.js file, where it's rendered and displayed in the DOM.

The important thing to remember about the App component is that there can only be one parent element (which in the example above is the <div> tag). Therefore, any element outside of that parent element will not be displayed in the UI.

Rendering the App Component Example

import React from 'react'; import ReactDOM from 'react-dom'; import App from './App'; ReactDOM.render( <React.StrictMode> <App /> </React.StrictMode>, document.getElementById('root') );

The code above displays the content of the index.js file that uses the render function to render the App component to the DOM using the document.getElementById(‘root’) method in the code above. This is made possible through the root Id used by the index.html file to present the following output in your browser:

Now You Can Create Components in ReactJS

This article provides you with a comprehensive view of the React library, and how to utilize it to create amazing user interfaces. With React, your user interfaces will not only perform well and look exactly how you want them to, but they’ll also be easy to maintain (thanks to components).

Now you can create professional user interfaces with the React library. But there’s no need to stop at React. There’s a range of other tools out there that can be used to supplement your front-end development process.

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