Technical question on how this application starts up

I am trying to understand the guts of this application and how it works.

How is root.jsx executed from Go? Can someone please explain in some level of detail how the Go backend connects with the React front end? How is it initially "booted up"? How does the webpack.config.js come into play?

I can see this line in root.html

<script>
    window.setup_root();
</script>

But I am not sure how it all connects.

thank you