title: MathJax.Hub.getAllJax returns empty array
body: <p>My html:</p>
  
  <p><code>&lt;span id="questiondisplay"&gt;{{question_display}}&lt;/span</code>></p>
  
  <p>Javascript code:</p>
  
  <pre><code>var math = MathJax.Hub.getAllJax("questiondisplay")
  </code></pre>
  
  <p>On doing this math is an empty array <code>[]</code></p>
  
  <p>However, on doing <code>$('#questiondisplay')</code> I get: <code>[&lt;span id="questiondisplay" class="ng-binding"&gt;&lt;/span&gt;]</code></p>
  
  <p>Can anyone please explain what I'm doing wrong with MathJax ?</p>