How to fallback from CDN to local JavaScript?

How to fallback from CDN to local JavaScript?

With JavaScript we can detect when our CDN-hosted JavaScript resources like jQuery or jQuery UI aren’t loaded successfully and try again to load them from local locations. The basic idea for CDN fallback is to check for a type or variable that should be present after a script load, and if it’s not there, try getting that script locally.

Is there a fallback for a CDN failure?

In this case, the CDN failure was extremely localized and relatively short but it could have been worse. A fallback technique like this would have allowed sites (like mine) to easily weather the storm. Scott Hanselman is a former professor, former Chief Architect in finance, now speaker, consultant, father, diabetic, and Microsoft employee.

Can a CSS file fall back to a CDN?

You may also want to take into account a fallback for the jQuery UI css file also, as you are more than likely to be using a CDN for this also. You can check for the visibility of an element with the class=”ui-helper-hidden”. If it is visible, then your CSS has not loaded and can fall back to the local version.

What should I do if my CDN goes down?

If a CDN is unavailable, you should fallback to serving the scripts from your own website, as otherwise a CDN going down could break your application, as shown below. I’m going to describe how to tackle that second point in this post, but the solutions will also cover the first point too.

When to use a CDN instead of a local file?

If you have many GB or Terabytes of static data and a heavy load for access to that content, a CDN can help with that. However, small, local sites or lightly loaded sites rarely need such things and a CDN can only add one more complication to your set up, operation and workflow, such as caching problems.

When to use CDN for CSS and JavaScript?

If your CSS and Javascript is static for all users then using a CDN is the right way to go. This would not cause any extra HTTP requests because it would only load the css and js files from the CDN instead of your own webserver (unless you are using inline code).

When to use a CDN for static files?

The CDN should be used for all static files (.css/.js/images). Sometimes however javascript or css files can have dynamic aspect to them such as that it would include a unique user string or something of that sort. In this situation the CDN server would have to contact the origin server on every request which would defeat the purpose.

When do you use local fallbacks in jQuery?

Local fallbacks for a CDN Let’s say your website’s front-end is dependent on a library like jQuery. When using a CDN, the resource should (depending on setup) deliver from the server that’s physically closest to the user.

How to add fallback attribute to CSS link?

You can add asp-fallback-* attributes to a link, and the tag helper automatically generates some JavaScript to check if the file was downloaded from the CDN correctly. However, if the CDN is unavailable, your site will look very broken. You can provide a fallback for a CSS stylesheet link, by adding the following attributes:

What happens to jQuery when the CDN is unavailable?

Upon discovering that the CDN is unavailable, the user’s browser could (in theory) hang for a significant length of time before giving up and falling back to the local copy. During this period, your jQuery plugins (or anything that’s called after jQuery) won’t load.

How to use bootstrap CDN when loading jQuery?

I’ve answered a similar question in How to use Bootstrap CDN? and, as Juhana said, the problem is the missing protocol when loading jQuery. The protocol-less CDN works when you are using http or https, because browsers will add the prefix to the jQuery URL with it.

When to fall back to a local copy of Google CDN?

If you’re concerned that the Google CDN ever fails or goes down, you can fall back to a local copy when the CDN is offline (this example is baked into templates like HTML5 Boilerplate): If you are having a custom jQuery UI theme, you have to host that on your own server. Google only hosts the main jQuery UI themes.

How to use Google CDN with jQuery UI?

Check out the jQuery UI Blog for a link of all CDN links http://blog.jqueryui.com/ If you’re concerned that the Google CDN ever fails or goes down, you can fall back to a local copy when the CDN is offline (this example is baked into templates like HTML5 Boilerplate):