onPageWillLeave() {
   // enable the root left menu when leaving the tutorial page
   this.app.getComponent('leftMenu').enable(true);
 }

 public openPage(page: any): void {
   // close the menu when clicking a link from the menu
   this.app.getComponent('leftMenu').close();
   // navigate to the new page if it is not the current page
   this.app.getComponent('nav').setRoot(page.component);
 };

 onPageDidEnter() {
   // the root left menu should be disabled on the tutorial page
   this.app.getComponent('leftMenu').enable(false);
 }