import { Component } from '@angular/core' ; @ Component ( { selector : 'app-root' , templateUrl : './app.component.html' , styleUrls : [ './app.component.css' ] } ) export class AppComponent { title = 'Structural Directives' ; extraContent = false ; users = [ { id : 10 , firstName : 'John' , lastName : 'Doe' } , { id : 20 , firstName : 'Joan' , lastName : 'Doe' } ] ; roles = [ { id : 0 , name : 'empty' } , { id : 1 , name : 'unknown' } , { id : 2 , name : 'user' } , { id : 3 , name : 'guest' } , { id : 4 , name : 'administrator' } ] ; selectedRole = 'empty' ; trackByUserId ( index , user ) { return user . id ; } }