Popular:
 Building Resilient Systems on AWS: Learn how to design and implement a resilient, highly available, fault-tolerant infrastructure on AWS.

JavaScript CDN Fallbacks

By  on  

CDNs are great for pulling shared resources from, especially JavaScript libraries. The advantage in the likelihood that a file is already cached before the user gets to our site is huge. The only problem with using a CDN is that it's out of control; more specifically, what if the CDN server is down? What a nightmare! Thousands if not millions of websites would be hurt...but not yours. Nope, you added a CDN fallback so that a failed CDN wouldn't hurt your site!

The HTML / JavaScript

The document.write method is one you generally want to avoid, but it works best in this case:

<!-- Use Google CDN for MooTools, local Moo as a callback -->
<script src="//ajax.googleapis.com/ajax/libs/mootools/1.4.1/mootools-yui-compressed.js"></script>
<script>!window.MooTools && document.write(unescape('%3Cscript src="/js/mootools-yui-compressed.js"%3E%3C/script%3E'))</script>

In the event that the CDN fails, your local file is instead used. Simple but clever fallback, yes? The likelihood that Google or other CDNs is down is small, but since you don't control the other server, there's always that risk! Play it safe!

Request Metrics real user monitoring
Request Metrics real user monitoring
Request Metrics real user monitoring
Request Metrics real user monitoring

Recent Features

  • By
    Send Text Messages with PHP

    Kids these days, I tell ya.  All they care about is the technology.  The video games.  The bottled water.  Oh, and the texting, always the texting.  Back in my day, all we had was...OK, I had all of these things too.  But I still don't get...

  • By
    5 HTML5 APIs You Didn&#8217;t Know Existed

    When you say or read "HTML5", you half expect exotic dancers and unicorns to walk into the room to the tune of "I'm Sexy and I Know It."  Can you blame us though?  We watched the fundamental APIs stagnate for so long that a basic feature...

Incredible Demos

  • By
    NSFW Blocker Using MooTools and CSS

    One of my guilty pleasures is scoping out the latest celebrity gossip from PerezHilton.com, DListed.com, and JoBlo.com. Unfortunately, these sites occasionally post NSFW pictures which makes checking these sites on lunch a huge gamble -- a trip to HR's office could be just a click away. Since...

  • By
    Custom Scrollbars in WebKit

    Before each of the browser vendors we like was providing unique CSS controls, Internet Explorer was setting the tone.  One such example is IE's early implementation of CSS filters. Internet Explorer was also the first browser that allowed developers to, for better or worse, customize...