JavaScript code: JavaScript Learning--code interpretation

I have added a note to this code and I hope it will help you.
<script type= "Text/javascript" charset= "Utf-8" >
(function () {
var doc = document,//defines individual names for the document object, and local variables are accessed faster than the global
WA = doc.createelement (' script '),//Create a <script> label
s = doc.getelementsbytagname (' script ') [0];//find the first <script> tag, it may be its own
Wa.type = ' text/javascript '//To add attributes to the <script> tag you just created, at this point: <script type= "Text/javascript" >
Wa.charset = ' utf-8 '; Set charset properties for labels,<script> don't need this, do you?
Wa.async = true; I don't know what it is, I've never seen it.
WA.SRC = (' https: ' = = Doc.location.protocol? ' https://': ' http://') + ' js.t.sinajs.cn/open/analytics/js/suda.js?version=20111118190824.js ';
Add src attribute to <script> tag, URL, if the current document's protocol is HTTPS https://otherwise http://then link to the path of JS js.t.sinajs.cn/open/analytics/js/ Suda.js?version=20111118190824.js
Finally, the label becomes
<script type= "Text/javascript" charset= "Utf-8" async= "true" src= "http (s)://js.t.sinajs.cn/open/analytics/js/ Suda.js?version=20111118190824.js "&GT;&LT;/SCR ipt>//Here I have manually added a space, otherwise it will be with the last script end tag conflict, this note
S.parentnode.insertbefore (WA, s);}) ()//finally add this tag to the page after the first <script> tag,
/*
The entire function is contained in an anonymous function to avoid conflicts with the name of the variable named outside.
The whole process is a dynamic loading of external JS file process, the advantage is that the browser will download the JS file in parallel, speed up the loading speed of the page.
In fact, at the end of the several doc to uninstall the reference is better,
doc = null;
WA = null;
s = null;
*/
</script>
This article links http://www.cxybl.com/html/wyzz/JavaScript_Ajax/20121211/34875.html