Javascript: Could not really understand the function return
<p>It is maybe incredibly easy but I couldn't solve what was going on.</p>

<pre><code>
function doSomething(a)
{
   var num=10;
   return setTimeout(
   function(){ a(num); }, 1000);
}
</code></pre>

<p>The only thing that actually confuses me is the <b>a(num)</b> part. What actually it does?<br/><b>Reminder: </b> I really am asking because I'm not familiar with the javascript syntax.</p>
