Ionic 2 PWA - Controlling browser back button

app.component.ts

import { IonicApp, App, MenuController } from 'ionic-angular';

@Component ({...})
export class MyWebApp {

  constructor (private _app: App, private _ionicApp: IonicApp, private _menu: MenuController) {

    platform.ready().then(() => {
      
      // Do your thing...
      this.setupBackButtonBehavior ();

    });
    
  }
  
  private setupBackButtonBehavior () {

    // If on web version (browser)
    if (window.location.protocol !== "file:") {

      // Register browser back button action(s)
      window.onpopstate = (evt) => {

        // Close menu if open
        if (this._menu.isOpen()) {
          this._menu.close ();
          return;
        }

        // Close any active modals or overlays
        let activePortal = this._ionicApp._loadingPortal.getActive() ||
          this._ionicApp._modalPortal.getActive() ||
          this._ionicApp._toastPortal.getActive() ||
          this._ionicApp._overlayPortal.getActive();

        if (activePortal) {
          activePortal.dismiss();
          return;
        }

        // Navigate back
        if (this._app.getRootNav().canGoBack()) this._app.getRootNav().pop();

      };

      // Fake browser history on each view enter
      this._app.viewDidEnter.subscribe((app) => {
        history.pushState (null, null, "");
      });

    }
    
  }

}

This is great, but it's not working well (Ionic 3). If I hit browser back button more that once, it will navigate back and in my case results in error as navigation stack is empty (no root).