Class Structure

// listener controller for Joint graph
class Controller extends joint.mvc.Listener {
    get context() {
        const [ctx = null] = this.callbackArguments;
        return ctx;
    }
}

// view controller, controlling display of shortest path with listeners
class ViewController extends Controller {
    startListening() {
        const { paper } = this.context;

        // activate functions with certain listeners
        this.listenTo(paper, {
            'element:pointerdown': selectSource,
            'element:mouseenter': selectEnd,
            'element:mouseleave': hidePathOnMouseLeave,
        });
    }
}

// edit controller with listening
class EditController extends Controller {
    startListening() {
        const { graph, paper } = this.context;

        // adding links
        this.listenTo(graph, {
            'change:source': replaceLink,
            'change:target': replaceLink,
        });

        // adding nodes
        this.listenTo(paper, {
            'element:mouseenter': showElementTools,
            'element:mouseleave': hideElementTools,
            'blank:pointerdblclick': addElement
        });
    }
}