title: What Typescript type is Angular2 event
body: <p>If I have the following button in an html file</p>
  
  <pre class="lang-html prettyprint-override"><code>&lt;button (click)="doSomething('testing', $event)"&gt;Do something&lt;/button&gt;
  </code></pre>
  
  <p>Also, in the corresponding component, I have this function</p>
  
  <pre><code>doSomething(testString: string, event){
      event.stopPropagation();
      console.log(testString + ': I am doing something');
  }
  </code></pre>
  
  <p>Is there a proper type that should be assigned to the <code>$event</code> input?
  The event parameter itself is an object, BUT if I assign it to a type object, I get an error</p>
  
  <blockquote>
    <p>Property 'stopPropogation' does not exist on type object</p>
  </blockquote>
  
  <p>So, what does Typescript consider the <code>$event</code> input?</p>