Use esbuild, rollup.js, or Webpack to bundle your JavaScript, then deliver it
via the asset pipeline in Rails. This gem provides installers to get you going
with the bundler of your choice in a new Rails application, and a convention to
use app/assets/builds to hold your bundled output as artifacts that are not
checked into source control (the installer adds this directory to .gitignore by
default).

You develop using this approach by running the bundler in watch mode in a
terminal with yarn build --watch (and your Rails server in another, if you're
not using something like puma-dev). You can also use ./bin/dev, which will start
both the Rails server and the JS build watcher (along with a CSS build watcher,
if you're also using cssbundling-rails).