how to get first child of a class's index using jquery?
<p>I have set of tr rows with a given class:</p>

<pre><code>           &lt;tr class="rowgroupA"&gt;&lt;td&gt;Test Data Logs&lt;/td&gt;&lt;/tr&gt;
           &lt;tr class="rowgroupA"&gt;&lt;td&gt;Test Data Logs&lt;/td&gt;&lt;/tr&gt;
           &lt;tr class="rowgroupA"&gt;&lt;td&gt;Test Data Logs&lt;/td&gt;&lt;/tr&gt;
           &lt;tr class="rowgroupA"&gt;&lt;td&gt;Test Data Logs&lt;/td&gt;&lt;/tr&gt;
           &lt;tr class="rowgroupB"&gt;&lt;td&gt;Test Data Logs&lt;/td&gt;&lt;/tr&gt; // I need this index
           &lt;tr class="rowgroupB"&gt;&lt;td&gt;Test Data Logs&lt;/td&gt;&lt;/tr&gt;
           &lt;tr class="rowgroupB"&gt;&lt;td&gt;Test Data Logs&lt;/td&gt;&lt;/tr&gt;
           &lt;tr class="rowgroupB"&gt;&lt;td&gt;Test Data Logs&lt;/td&gt;&lt;/tr&gt;
</code></pre>

<p>To be more specific, how would I get the first-child of class name rowgroupB's index using jquery?</p>
