Private parameters in Typescript : <p>I am learning <code>Angular2</code> and working with <code>classes</code> in <code>javascript</code> first time.</p>

<p>What does the <code>private</code> parameter and why it couldn't be simply <code>heroService: HeroService</code> ? </p>

<pre><code>constructor(private heroService: HeroService) { }
</code></pre>
