import { Observable } from "tns-core-modules/data/observable" ; export class PersonBaseViewModel extends Observable { private _person : PersonBase ; get person ( ) { if ( ! this . _person ) { this . _person = new PersonBase ( "John" , 23 , "1993-05-16" ) ; } return this . _person ; } } export class PersonBase { public name : string ; public age : number ; public birthDate : string ; constructor ( name , age , birthDate ) { this . name = name ; this . age = age ; this . birthDate = birthDate ; } }