title: what does '<Hero[]>' mean
body: <p>hi I'm new to <code>angular</code> and <code>typescript</code>, and I'm trying to learn the tutorial from <a href="https://angular.io/tutorial/toh-pt6" rel="nofollow noreferrer">angular</a>. and I found something that I don't understand what it meant. like:</p>
  
  <p>1.</p>
  
  <pre><code>getHeroes(): Observable&lt;Hero[]&gt; {
      this.messageService.add('HeroService: fetched heroes');
      console.log(this.http);
      return this.http.get&lt;Hero[]&gt;(this.heroesUrl);
  }
  </code></pre>
  
  <p>on the above example, i want to know what does <code>&lt;Hero[]&gt;</code> means on <code>Observable&lt;Hero[]&gt;</code> and <code>this.http.get&lt;Hero[]&gt;(this.heroesUrl)</code></p>
  
  <p>2.</p>
  
  <pre><code>getHero(id: number): Observable&lt;Hero&gt; {
      this.messageService.add(`HeroService: fetched hero id=${id}`);
      return of(HEROES.find(hero =&gt; hero.id === id));
  }
  </code></pre>
  
  <p>check it carefully on <code>HeroService: fetched hero id=${id}</code> it wrapped with backticks (`) not single quote ('). why use it?
  and last one the <code>HEROES.find(hero =&gt; hero.id === id)</code> what does <code>=&gt;</code> means?</p>
  
  <p>I'm really new to this. so, I'm so sorry if my questions offend or trigger you guys.. </p>
  
  <p>Thank you!</p>