title: Count of "Defined" Array Elements
body: <p>Given following array:</p>
  
  <pre><code>var arr = [undefined, undefined, 2, 5, undefined, undefined];
  </code></pre>
  
  <p>I'd like to get the count of elements which <em>are</em> defined (i.e.: those which are <em>not</em> <code>undefined</code>).  Other than looping through the array, is there a good way to do this?</p>