Add base app

app/javascript/controllers/application.js

@@ -0,0 +1,9 @@
+import { Application } from "@hotwired/stimulus"
+
+const application = Application.start()
+
+// Configure Stimulus development experience
+application.debug = false
+window.Stimulus   = application
+
+export { application }

app/javascript/controllers/hello_controller.js

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+import { Controller } from "@hotwired/stimulus"
+
+export default class extends Controller {
+  connect() {
+    this.element.textContent = "Hello World!"
+  }
+}

app/javascript/controllers/index.js

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+// Import and register all your controllers from the importmap under controllers/*
+
+import { application } from "controllers/application"
+
+// Eager load all controllers defined in the import map under controllers/**/*_controller
+import { eagerLoadControllersFrom } from "@hotwired/stimulus-loading"
+eagerLoadControllersFrom("controllers", application)
+
+// Lazy load controllers as they appear in the DOM (remember not to preload controllers in import map!)
+// import { lazyLoadControllersFrom } from "@hotwired/stimulus-loading"
+// lazyLoadControllersFrom("controllers", application)