Who can give me about this grammar in javascript
<pre><code>function getTime(zone, success) {
var url = 'http://json-time.appspot.com/time.json?tz=' + zone,
    ud = 'json' + (+new Date());
window[ud]= function(o){
    success &amp;&amp; success(new Date(o.datetime), o);
};
document.getElementsByTagName('head')[0].appendChild((function(){
    var s = document.createElement('script');
    s.type = 'text/javascript';
    s.src = url + '&amp;callback=' + ud;
    return s;
})());}
</code></pre>

<p>What is the use of <code>window[ud]</code> and what does <code>success &amp;&amp; success()</code> mean?
Another question is why we need an extra pair of brackets in the last line when calling appendChild outside its anonymous funtion?</p>

<p>Thanks.</p>
