How to fallback to local stylesheet (not script) if CDN fails

Not cross-browser tested but I think this will work. Will have to be after you load jquery though, or you'll have to rewrite it in plain Javascript.

<script type="text/javascript">$.each(document.styleSheets, function(i,sheet){  if(sheet.href=='http://code.jquery.com/mobile/1.0b3/jquery.mobile-1.0b3.min.css') {    var rules = sheet.rules ? sheet.rules : sheet.cssRules;    if (rules.length == 0) {      $('<link rel="stylesheet" type="text/css" href="path/to/local/jquery.mobile-1.0b3.min.css" />').appendTo('head');    } }})</script>

One could use onerror for that:

<link rel="stylesheet" href="cdn.css" onerror="this.onerror=null;this.href='local.css';" />

The this.onerror=null; is to avoid endless loops in case the fallback it self is not available. But it could also be used to have multiple fallbacks.

However, this currently only works in Firefox and Chrome.

Update: Meanwhile, this seems to be supported by all common browsers.

Assuming you are using the same CDN for css and jQuery, why not just do one test and catch it all??

<link href="//ajax.googleapis.com/ajax/libs/jqueryui/1/themes/start/jquery-ui.css" rel="stylesheet" type="text/css" /><script type="text/javascript" src="//ajax.googleapis.com/ajax/libs/jquery/1/jquery.min.js"></script><script type="text/javascript" src="//ajax.googleapis.com/ajax/libs/jqueryui/1/jquery-ui.min.js"></script><script type="text/javascript">    if (typeof jQuery == 'undefined') {        document.write(unescape('%3Clink rel="stylesheet" type="text/css" href="../../Content/jquery-ui-1.8.16.custom.css" /%3E'));        document.write(unescape('%3Cscript type="text/javascript" src="/jQuery/jquery-1.6.4.min.js" %3E%3C/script%3E'));        document.write(unescape('%3Cscript type="text/javascript" src="/jQuery/jquery-ui-1.8.16.custom.min.js" %3E%3C/script%3E'));    }</script>