NativeScript/e2e/dev-tools-drawer/app/app-root/app-root-view-model.ts

import { Observable } from "tns-core-modules/data/observable";

import { ObservableProperty } from "../shared/observable-property-decorator";
import { SelectedPageService } from "../shared/selected-page-service";

export class AppRootViewModel extends Observable {
    @ObservableProperty() selectedPage: string;

    constructor() {
        super();

        SelectedPageService.getInstance().selectedPage$
        .subscribe((selectedPage: string) => this.selectedPage = selectedPage);
    }
}