The intent of this post is to help people build and understand simple reactive web applications
2025 update: due to the never-ending nature of tech breaking things - this post needed an update (goodbye Create React App)
https://react.dev/blog/2025/02/14/sunsetting-create-react-app
Pre-Requisites
install node.js (which also includes npm) from https://nodejs.org/en
check if they are installed:
node -v
npm -v
Install the default react project
in a directory (probably a code repository)
npm create vite@latest my-app -- --template react
cd my-app
npm install
npm run dev
(obsolete: npx create-react-app my-app)
note that npm run dev starts a web server at http://localhost:5173
Essential folder structure (that is created by the framework with default files)
my-app/
index.html (this is the entrypoint, yes it's all just html and http ;)
src/
index.css (this is for styles for the output - if you want things to look good)
main.jsx (connects the App to the starting index.html entrypoint)
App.css
App.jsx (this is where you add code)
/public is a directory with image or binary files that are served directly
(Remove the "vitals" phone home stats because privacy should be a default)
INDEX.HTML
The defacto web standard for the first document (for a web server) to return when no resource is specified is "index.html"
https://en.wikipedia.org/wiki/HTML
<!DOCTYPE html>
<html lang="en"><body>
<noscript>You need to enable JavaScript to run this app.</noscript>
<div id="root"></div>
<script type="module" src="/src/main.jsx"></script>
</body></html>
MAIN.JSX
// this wrapper is connecting the App to the root
import React from 'react'
import ReactDOM from 'react-dom/client'
import './index.css';
import App from './App.jsx'
const rootElement = document.getElementById("root");
const root = ReactDOM.createRoot(rootElement);
root.render(
<React.StrictMode>
<App />
</React.StrictMode>
);
APP.JSX
// very simple app that switches the content displayed when the button is clicked
import './App.css';
import { useState } from 'react';
const content = [
["hello world", "more content on line 2"],
["react.dev has tutorials and documentation"]
];
function App() {
const [activeContentIndex, activeContent] = useState(0);
return (
<div className="App">
<header className="App-header">
</header>
<div id="tabs">
<button onClick={() => activeContent(0)}>Tab 1</button>
<button onClick={() => activeContent(1)}>Tab 2</button>
</div>
<div id="tab-content">
{content[activeContentIndex].map((line, i) => <p key={i}>{line}</p>)}
</div>
</div>
);
}
export default App;
A React component is a JavaScript function that returns JSX (looks like HTML but is not HTML)
Build and Deploy
A critical file created by the default app generation is package.json, it lists all your project dependencies and scripts (including "how to build")
The build framework reads your package.json to understand which tools to run, in this case vite compiles/reformats the code into a production bundle of files that can be uploaded to a server
The command to "build", or convert all of these files into a single bundle that is easily deployed:
npm run build
The new output directory dist contains the index.html and static files along with "minified" javascript and css