Question

A client’s website was depending on the jquerytools.org CDN, which is currently not working and therefore his site is broken (disregarding graceful Javascript degradation). He could host the relevant files locally, but then he does not get the advantages of a CDN. How bad is it to reference ostensibly the same Javascript file on two independent CDNs in the interest of redundancy?

<script src="http://cdn.jquerytools.org/1.2.7/full/jquery.tools.min.js"></script>
<script src="http://jquerytools.flowplayer.netdna-cdn.com/1.2.6/all/jquery.tools.min.js"></script>

Answer 1

You should check if the first CDN actually delivered jQuery before you load the second script:

<script src="http://cdn.jquerytools.org/1.2.7/full/jquery.tools.min.js"></script>
<script type="text/javascript">
if (typeof jQuery.tools === 'undefined') {
    document.write('<script src="http://jquerytools.flowplayer.netdna-cdn.com/1.2.6/all/jquery.tools.min.js"><\/script>');
}
</script>