adrienpoly/application.html.erb

## application.html.erb
<!DOCTYPE html>
<html>
  <head>
    ...
  </head>

  <body data-controller="js">
    <%= yield %>
  </body>
</html>

## js_controller.js
import { Controller } from 'stimulus'

export default class extends Controller {
  static values = { loaded: Boolean }

  connect() {
    this.loadedValue = true
  }
}

## some_system_test_spec.rb
# ...
scenario 'test some js behavior', js: true do
  visit some_path
  ensure_js_is_ready

  # JS is fully loaded you can start interacting with the page
end
# ...

## system_spec_helpers.rb
def ensure_js_is_ready
  expect(page).to have_css('[data-js-loaded-value="true"]')
end
	<!DOCTYPE html>
	<html>
	<head>
	...
	</head>

	<body data-controller="js">
	<%= yield %>
	</body>
	</html>
	import { Controller } from 'stimulus'

	export default class extends Controller {
	static values = { loaded: Boolean }

	connect() {
	this.loadedValue = true
	}
	}
	# ...
	scenario 'test some js behavior', js: true do
	visit some_path
	ensure_js_is_ready

	# JS is fully loaded you can start interacting with the page
	end
	# ...
	def ensure_js_is_ready
	expect(page).to have_css('[data-js-loaded-value="true"]')
	end