serialize variable merge?
<p>I want to add data of <code>ExtrasGroupID</code> variable into <code>options</code> serialize variable (or what is other way), how can that be done?</p>

<p>Example below:</p>

<pre><code>var ExtrasGroupID = $("#SelectExtrasGroup option:selected").val();
var options = $("#FormExtrasOptionsList").serialize();

$.post("ajax.php", options,
  function(data)  {
        console.log(data)
  });
</code></pre>
