引用google libraries

1. Google Libraries API - Developer's Guide
   還挺多的
   

   
   Available Libraries
   

   Chrome Frame

   Dojo

   Ext Core

   jQuery

   jQuery UI

   MooTools

   Prototype

   script_aculo_us

   SWFObject

   Yahoo! User Interface Library (YUI)

   WebFont Loader

   
   用法也很簡單，像jquery就先到該文件下找"path"，再放入src就好啦
   <!-- jquery -->
<script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/1.4.3/jquery.min.js"></script>

<!-- jquery ui -->
<script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jqueryui/1.8.6/jquery-ui.min.js"></script>
   


2. dynamically load jquery if 'jQuery' does not exist
   function initJQuery() {
   //if the jQuery object isn't available
   if (typeof(jQuery) == 'undefined') {
     if (typeof initJQuery.jQueryScriptOutputted == 'undefined') {
       //only output the script once..
       initJQuery.jQueryScriptOutputted = true;
       //output the script (load it from google api)
       document.write("");
     }   
     setTimeout("initJQuery()", 50);
   } else {
     (function($){ // CLOSURE -> save to use $
        $.fn.foo = function(input) {
        alert("foo:" + input) ;
      } ;
     })(jQuery) ;
   }

   window.onload = function() {
   $('body').foo("bar") ; // won't necessarily fire if jQuery loads after   document load
  }
}
initJQuery();