app/javascript/controllers/index.js
// Load all the controllers within this directory and all subdirectories.
// Controller files must be named *_controller.js.
import { Application } from 'stimulus';
import { definitionsFromContext } from 'stimulus/webpack-helpers';
const application = Application.start();
const context = require.context('controllers', true, /_controller\.js$/);
application.load(definitionsFromContext(context));