问英雄在使用.subscribe方法的服务内部绑定了什么？

EN

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

@Component({
  selector: 'app-heroes',
  templateUrl: './heroes.component.html',
  styleUrls: ['./heroes.component.css']
})
export class HeroesComponent implements OnInit {

  heroes: Hero[];

selectedHero: Hero;

onSelect(hero: Hero): void {
  this.selectedHero = hero;
}

getHeroes(): void {
  this.heroService.getHeroes()
      .subscribe(heroes => this.heroes = heroes);
}

constructor(private heroService : HeroService) {}


 ngOnInit() { 
    this.getHeroes();
  }

}

import { Injectable } from '@angular/core';
import { Hero } from './heroes/hero';
import { HEROES } from './heroes/mock.heroes';
import { Observable, of } from 'rxjs';
import { HeroesComponent } from './heroes/heroes.component';

@Injectable({
  providedIn: 'root'
})
export class HeroService {

  getHeroes(): Observable<Hero[]> {
    return of(HEROES);
  }

  constructor() { }
}

heroes: Hero[];