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
    Creating Scrolling Parallax Effects with CSS

    Introduction For quite a long time now websites with the so called "parallax" effect have been really popular. In case you have not heard of this effect, it basically includes different layers of images that are moving in different directions or with different speed. This leads to a...

  • By
    How I Stopped WordPress Comment Spam

    I love almost every part of being a tech blogger:  learning, preaching, bantering, researching.  The one part about blogging that I absolutely loathe:  dealing with SPAM comments.  For the past two years, my blog has registered 8,000+ SPAM comments per day.  PER DAY.  Bloating my database...

Incredible Demos