title: which number has div with specific class
body: <p>I would like to have number (int) of ul with class 'currentWeek'. My html look like this:</p>
  
  <pre><code>&lt;div class="calendarContainer"&gt;
      &lt;ul&gt;
          &lt;li&gt;&lt;/li&gt;
          &lt;li&gt;&lt;/li&gt;
          &lt;li&gt;&lt;/li&gt;
      &lt;/ul&gt;
      &lt;ul&gt;
          &lt;li&gt;&lt;/li&gt;
          &lt;li&gt;&lt;/li&gt;
          &lt;li&gt;&lt;/li&gt;
      &lt;/ul&gt;
      &lt;ul class="currentWeek"&gt;
          &lt;li&gt;&lt;/li&gt;
          &lt;li&gt;&lt;/li&gt;
          &lt;li&gt;&lt;/li&gt;
      &lt;/ul&gt;
      &lt;ul&gt;
          &lt;li&gt;&lt;/li&gt;
          &lt;li&gt;&lt;/li&gt;
          &lt;li&gt;&lt;/li&gt;
      &lt;/ul&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>this is how I could all UL's </p>
  
  <pre><code>var weeksCount = widget.find(".calendarContainer").children().length;
  </code></pre>
  
  <p>But I have no idea how to know that currentWeek is third</p>
  
  <p>Many thanks!</p>