title: How to test undefined in transcrypt
body: <p>I need to test if a javascript object attribute exists.</p>
  
  <p>For example to see if a jquery extension is available. The next line returns <em>undefined</em> in the browser console :</p>
  
  <blockquote>
    <p>$("#myid").toc</p>
  </blockquote>
  
  <p>I want to test this value in transcrypt, I tried :</p>
  
  <blockquote>
    <p>getattr(S ("#myid"), "toc") is None</p>
  </blockquote>
  
  <p>but it doesn't work :-/</p>