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
    Chris Coyier&#8217;s Favorite CodePen Demos

    David asked me if I'd be up for a guest post picking out some of my favorite Pens from CodePen. A daunting task! There are so many! I managed to pick a few though that have blown me away over the past few months. If you...

  • By
    Facebook Open Graph META Tags

    It's no secret that Facebook has become a major traffic driver for all types of websites.  Nowadays even large corporations steer consumers toward their Facebook pages instead of the corporate websites directly.  And of course there are Facebook "Like" and "Recommend" widgets on every website.  One...

Incredible Demos

  • By
    PHP / MooTools 1.2 Accordion Helper

    The MooTools Accordion plugin seems to be the plugin that people seem to have the most problems with. It's an awesome plugin, so I can see why so many people want to use it, but I think that may be part of the problem.

  • By
    MooTools 1.2 Image Protector: dwProtector

    Image protection is a hot topic on the net these days, and why shouldn't it be? If you spent two hours designing an awesome graphic, would you want it ripped of in matter of seconds? Hell no! That's why I've created an image...