**Title:** Dive into React: Building Responsive Web Applications with the Latest JavaScript Library

**Subtitle:** Creating a Responsive App Using React, Purely with JavaScript

**

Introduction

**

Welcome to our deep dive into React, a powerful JavaScript library for building user interfaces. Today, we will explore how to build a responsive web application using React, without any external CSS styles. This exercise will help you understand the core principles of React and how it handles the rendering of components.

**

Getting Started

**

First, ensure you have Node.js and npm installed on your machine. If you don’t have them, you can download them from [Node.js](https://nodejs.org/) and [npm](https://www.npmjs.com/) respectively.

Next, create a new directory for your project and navigate to it in your terminal:

“`bash
mkdir react-no-css-app && cd react-no-css-app
“`

Initialize a new npm project and install the required dependencies:

“`bash
npm init -y
npm install –save react react-dom
“`

Create a new file named `index.js` in your project directory and open it in your preferred code editor.

**

Creating a Functional Component

**

Functional components in React are simple JavaScript functions that return a React element. Let’s create a basic functional component that displays a simple message:

“`javascript
function Welcome(props) {
return

Hello, {props.name}

;
}
“`

**

Rendering the Component

**

Now, let’s render our `Welcome` component using the `ReactDOM.render()` method:

“`javascript
ReactDOM.render(, document.getElementById(‘root’));
“`

Make sure to add the following line at the beginning of your `index.js` file to allow JSX syntax:

“`javascript
/** @jsx React.DOM */
“`

Finally, add an empty `div` with an `id` of `root` to your `index.html` file:

“`html

“`

**

Building a Responsive App

**

To make our app responsive, we will use the `props` to dynamically adjust the component’s size based on the viewport. Modify the `Welcome` component as follows:

“`javascript
function Welcome(props) {
const { size } = props;
let style = {
fontSize: `${size}px`,
margin: ‘0 auto’,
display: ‘block’,
textAlign: ‘center’,
width: `${size * 2}px`,
};

return

Hello, {props.name}

;
}
“`

Now, let’s pass the `size` prop to our `Welcome` component, and adjust it based on the viewport width:

“`javascript
function App() {
const viewportWidth = window.innerWidth;
const viewportHeight = window.innerHeight;

const size = Math.min(viewportWidth, viewportHeight) / 3;

return ;
}

ReactDOM.render(, document.getElementById(‘root’));
“`

Run your application using the following command:

“`bash
npm start
“`

This simple example demonstrates how to build a responsive web application using React, exclusively with JavaScript. As you continue to explore React, you’ll discover more powerful ways to create engaging user interfaces and build scalable web applications. Happy coding!