panel/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"

const application = Application.start()

import GeoController from "./geo_controller";
import ReorderController from "./reorder_controller";

application.register("geo", GeoController);
application.register("reorder", ReorderController);