Getting undefined error notice in console even though I'm checking for undefined
<p>This code:</p>

<pre><code>if(typeof(Listings.page_num) != 'undefined') {
   // something
}
</code></pre>

<p>Triggers this notice in firebug console:</p>

<pre><code>Listings is not defined http://mysite.com/js/content_ads.js Line 13
</code></pre>

<p>Well duh, that's why I checked! Is there any way to get rid of this notice?</p>
