Firefox not able to enumerate document.styleSheets[].cssRules[]

Question

Here is the code:

• http://jsfiddle.net/salman/2hyYg/
• http://jsfiddle.net/salman/2hyYg/show/

You'll notice the alert(document.styleSheets[x].cssRules.length) fails with a "security exception". Any workaround for this. I am asking because there are a couple of "CSS lazy loading" classes out there that use this feature to detect if the CSS document is loaded.

Also: is the security exception a correct behavior/does it conform to standards?

Answer 1

You can get that error when trying to read a stylesheet loaded from a different domain or server, or trying to read an @import rule.

For your purpose, just check the document.styleSheets.length .

Answer 2

As of 2013, you can set the "crossorigin" attribute on the <link>-Element to signal the browser that this CSS is trusted (https://developer.mozilla.org/en-US/docs/Web/HTML/Element/link).

After that, you can access its rules via Javascript.