Where's the connection between index.html and index.js in a Create-React-App application?
I'm starting to play with the Create React App, but I can't understand how the index.js is loaded inside index.html. This is the html code:
<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="shortcut icon" href="%PUBLIC_URL%/favicon.ico">
<!--
Notice the use of %PUBLIC_URL% in the tag above.
It will be replaced with the URL of the `public` folder during the build.
Only files inside the `public` folder can be referenced from the HTML.
Unlike "/favicon.ico" or "favicon.ico", "%PUBLIC_URL%/favicon.ico" will
work correctly both with client-side routing and a non-root public URL.
Learn how to configure a non-root public URL by running `npm run build`.
-->
<title>React App</title>
</head>
<body>
<div id="root"></div>
<!--
This HTML file is a template.
If you open it directly in the browser, you will see an empty page.
You can add webfonts, meta tags, or analytics to this file.
The build step will place the bundled scripts into the <body> tag.
To begin the development, run `npm start`.
To create a production bundle, use `npm run build`.
-->
</body>
</html>
But I can't see anywhere the import of the index.js. Where is the connection? What am I missing?
Answer
Under the hood, Create React App uses Webpack with html-webpack-plugin.
Our configuration specifies that Webpack uses src/index.js as an “entry point”. So that’s the first module it reads, and it follows from it to other modules to compile them into a single bundle.
When webpack compiles the assets, it produces a single (or several if you use code splitting) bundles. It makes their final paths available to all plugins. We are using one such plugin for injecting scripts into HTML.
We have enabled html-webpack-plugin to generate the HTML file. In our configuration, we specified that it should read public/index.html as a template. We have also set inject option to true. With that option, html-webpack-plugin adds a <script> with the path provided by Webpack right into the final HTML page. This final page is the one you get in build/index.html after running npm run build, and the one that gets served from / when you run npm start.
Hope this helps! The beauty of Create React App is you don’t actually need to think about it.