import { Observable } from 'data/observable' ; export class HelloWorldModel extends Observable { private _counter : number ; private _message : string ; constructor ( ) { super ( ) ; this . _counter = 42 ; this . updateMessage ( ) ; } get message ( ) : string { return this . _message ; } set message ( value ) { if ( this . _message !== value ) { this . _message = value ; this . notifyPropertyChange ( 'message' , value ) ; } } public onTap ( ) { this . _counter -- ; this . updateMessage ( ) ; } private updateMessage ( ) { if ( this . _counter <= 0 ) { this . message = 'Hoorraaay! You unlocked the NativeScript clicker achievement!' ; } else { this . message = `${ this . _counter } taps left` ; } } }