Add 'are you sure?' style accidental page refresh prevention

src/app/app.component.ts

@@ -17,5 +17,10 @@ export class AppComponent implements OnInit {
 
   ngOnInit() {
     this.titleService.setTitle(this.documentTitle);
+    window.addEventListener('beforeunload', (event) => {
+      const confirmationMessage = 'Refreshing this page may mess up your challenge/tutorial state. Are you sure?';
+      event.returnValue = confirmationMessage;
+      return confirmationMessage;
+    });
   }
 }