title: Call javascript method variable loses 'this'
body: <p>I've created a simple pointer to a method like so:</p>
  
  <pre><code>export class SmbwaService {
      getExistingArsByLab(labId: number): Observable&lt;SmwbaAr[]&gt; {
          this.otherMethod();
      }
  
      otherMethod(): void {
      }
  }
  
  
  let method: (x: number) =&gt; Observable&lt;SmbwaAr[]&gt;;
  method = this.service.getExistingArsByLab;
  method(12);
  </code></pre>
  
  <p>That executes OK insofar as it does call <code>getExistingArsByLab</code> method.  However, I then get an error when it tries to call <code>otherMethod</code> because:</p>
  
  <blockquote>
    <p>Cannot read property otherMethod of undefined.</p>
  </blockquote>
  
  <p>What's the right way to do this?  Obviously in my actual code <code>method</code> is being set to one of a number of different methods based on some conditions.</p>