$ npm install
Open two terminals.
In the first one, start sbt and, within, continuously build the Scala.js project:
$ sbt
...
> ~fastLinkJS
...
In the second one, start the Vite development server with
$ npm run dev
...
Follow the URL presented to you by Vite to open the application.
You can now continuously edit the Main.scala file, and Vite will automatically reload the page on save.
Make a production build with
$ npm run build
You can then find the built files in the dist/ directory.
You will need an HTTP server, such as python3 -m http.server, to open the files, as Vite rewrites <script> tags to prevent cross-origin requests.