get the id of the class which has class active?

I want to get the id of the id of the element which has class active. I've viewed this thread , but isnt able to get the o/p I want.

<ul class="nav nav-pills nav-stacked navigation" id="configuration_sidebar_content">
     <li>
        <a>Location</a>
        <ul class="nav nav-pills nav-stacked " id="location" style="padding-left:30px;">
            <li class="active" id="region"><a>Region</a></li>
            <li id="country"><a>Country</a></li>
        </ul>
     </li>
     <li>
         <a>Device</a>
         <ul class="nav nav-pills nav-stacked" style="padding-left:30px;">
              <li id="gateway_unit"><a>Gateway Unit</a></li>
              <li id="meter_unit"><a>Meter Unit</a></li>
         </ul>
     </li>
 </ul>

I tried this.

selected_item_id = $("#configuration_sidebar_content li.a.active").attr('id')