inheritance - Angular 2 Typescript inheratance state-pattern issue -

i'm uning typescript inheritance implement state pattern i'm getting runtime error when new superclass. hoping find out why or what's wrong, thanks.

working plunker: https://plnkr.co/edit/xscxr4?p=preview

vehicle.ts import { car } "./car";

export class vehicle {    description: string = "generic vehicle";    swap(app: appcomponent): void {      app.vehicle = this.iscar(app) ? new vehicle() : new car();   }    /* helper demo purposes */   private iscar(app: appcomponent) {     return app.vehicle instanceof car;   }  } 

car.ts

import { vehicle } "./vehicle";  export class car extends vehicle {   description: string = "car"; } 

it's state-pattern. vehicle type 'vehicle' or 'car' can swap instance in 'appcomponent'

app.component.ts

import { component, oninit } '@angular/core'; import { vehicle }  "./vehicle"; import { car }  "./car";  @component({   moduleid: module.id,   selector: 'my-app',   templateurl: 'app.component.html', }) export class appcomponent implements oninit {   vehicle: vehicle;    swap(): void {     this.vehicle.swap(this);   }    ngoninit() {     //no problems works     //this.vehicle = new car();       //error: typeerror: cannot read property 'prototype' of undefined(…)     this.vehicle = new vehicle();   }  } 

if initialize 'car' instance (subtype) there no problem.

if initialize 'vehicle' instance (supertype) js runtime error

error: typeerror: cannot read property 'prototype' of undefined(…) 

i'd know why because seems legitimate thing do.

what doing wrong here?

in plunker, in app.component.ts replace

this.vehicle = new car()  

with

 this.vehicle = new vehicle() 

to see issue.

thanks john