title: Disable SUBMIT button until select box choices
body: <p>I have a small form.</p>
  
  <p>Two select box elements and a submit button.</p>
  
  <p>The select box elements collectively when selections are chosen, fire off an ajax request.</p>
  
  <p>What I want to do is, disable the submit button UNTIL user has made selections from the select drop downs.</p>
  
  <p>They must make a selection from BOTH select drop downs, before the Submit button is enabled.</p>
  
  <p>I dont mind if the submit button is hidden until selections made.</p>
  
  <p>Brief Code:</p>
  
  <pre><code>&lt;form id="ad_form" method="post" action=""&gt;
      &lt;p&gt;
          &lt;select id="ad_type" name="ad_type"&gt;
              &lt;option value="" selected="selected"&gt;Select premium ad type&lt;/option&gt;
              &lt;option value="&lt;?php echo TYPE_USER;?&gt;"&gt;Featured Agent&lt;/option&gt;
              &lt;option value="&lt;?php echo TYPE_LISTING;?&gt;"&gt;Featured Listing&lt;/option&gt;
          &lt;/select&gt;
          &lt;label for="ad_type" class="labelStrong"&gt;Advertising Type&lt;/label&gt;
      &lt;/p&gt;
      &lt;p&gt;
          &lt;select id="ad_duration" name="ad_duration"&gt;
              &lt;option value="" selected="selected"&gt;Select premium ad duration&lt;/option&gt;
              &lt;option value="weekly"&gt;Weekly&lt;/option&gt;
              &lt;option value="fortnightly"&gt;Fortnightly&lt;/option&gt;
              &lt;option value="monthly"&gt;Monthy&lt;/option&gt;
          &lt;/select&gt;
          &lt;label for="ad_duration" class="labelStrong"&gt;Advertising Duration&lt;/label&gt;
      &lt;/p&gt;
  
      &lt;p&gt;
          &lt;div id="calender"&gt;
          &lt;/div&gt;
      &lt;/p&gt;
      &lt;p&gt;
          &lt;input type="submit" name="submit" value="Submit" id="submitorder" /&gt;
      &lt;/p&gt;
  &lt;/form&gt;
  </code></pre>