import { Observable } from "tns-core-modules/data/observable"; export class HelloWorldModel extends Observable { private _counter: number; private _message: string; constructor() { super(); // Initialize default values. this._counter = 42; this.updateMessage(); } get message(): string { return this._message; } set message(value: string) { if (this._message !== value) { this._message = value; this.notifyPropertyChange("message", value); } } 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`; } } }