Hi. Thanks for the question. Let me explain it as best as I can.

ReactUnity works similarly to how a regular React Web application built with Webpack works. Therefore, it is best if I explain it by making an analogy between React Web application and React Unity application.

In a React Web application, you have a React project, which has a package.json in its root. You use Node.js to run a development server, or build your application. You also have a package manager (npm, yarn etc.) that installs the dependencies in your package.json. This is all true for ReactUnity projects as well.

Web applications often use a framework (Angular, Next.js etc.) or a bundler (Webpack, Vite, Rollup etc.). ReactUnity uses Webpack. In fact, it uses a Webpack config very similar to Create React App.

Anyway, Webpack has something called a dev-server. When you run it, it serves your Html and Javascript files so that you can preview your application by going to a URL (for example http://localhost:8080) in your browser. Dev server also provides other benefits like hot-reload and compile errors. This is also possible in ReactUnity. When you run your dev-server, a component inside Unity (ReactUnityRenderer) can connect to this server and run the Javascript code that is served, to generate the UI inside Unity.

Note though, ReactUnity doesn't have HTML files. It works with Javascript and CSS.

You can also build your project with Webpack, which generates static Html/Javascript/Css files. These files can then be served with any web server you want (Nginx, IIS, Apache, Express, etc. there are too many). When you serve them, someone on internet can go to the URL of your server and see your website. We don't need that in ReactUnity. In ReactUnity, when you build your static Javascript/Css files, you build them into your Unity project. ReactUnityRenderer can then read those files and generate your UI inside Unity.

In short, a ReactUnity UI is similar to a React Website. React Websites are rendered in a browser, but ReactUnity UI is rendered using the ReactUnityRenderer component that is in the ReactUnity's Core package.

The renderer boots up a Javascript Runtime inside unity and executes the Javascript built by your project. This is similar to a browser's Javascript engine. In ReactUnity, you can select one of the three JS runtimes you want to run your UI in, QuickJS (recommended), Clearscript, and Jint. Each has advantages and disadvantages. I won't go into details.

Let me know if there is a gap.