app.component.ts file

```
import { Component, OnInit } from '@angular/core';
import { Hero } from './hero';
import { HeroService } from './hero.service';

@Component({
  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.css'],
  providers: [HeroService]
})

export class AppComponent implements OnInit{
  title = 'Tour of Heroes';
  heroes : Hero[ ];
  selectedHero : Hero;
  constructor(private heroService: HeroService) { }
      getHeroes(): void {
     this.heroService.getHeroes().then(heroes => this.heroes = heroes);
  };
    ngOnInit(): void {
    this.getHeroes();
  };
    onSelect(hero: Hero): void{
    this.selectedHero = hero;
  };
}

```

**hero.service.ts** 

```
import { Injectable } from '@angular/core'; 
import { Hero } from './hero'; 
import { HEROES } from './mock-heroes'; 

@Injectable() 
export class HeroService { 

    getHeroes(): Promise<Hero[]> { 
        return Promise.resolve(HEROES); 
    } 
}

```

How to resolve this error?