检查jQuery CDN，回退到本地版本

Posted 2021-02-24

Use CDN if online. Fallback to local version if offline.

<!-- Google AJAX Libraries - jQuery 1.7.1 at 2011-12 -->
    <script src="http://www.google.com/jsapi"></script>
    <script type="text/javascript">
    	google.load("jquery", "1.7.1");
    </script>
 
    <!-- Let's check if we are on or off line -->
    <script type="text/javascript">!window.jQuery && document.write(unescape('%3Cscript type="text/javascript" src="js/jquery-1.7.1.min.js"%3E%3C/script%3E'))</script>