Event for browser tab hidden/shown?

Is there any DOM event for when the browser tab loses/gains focus? I know there are the blur and focus events on window, but they also fire when the browser window as a whole loses focus. The browser might then be still visible to the user. Of course such an event would be browser specific, but that's ok.

The reason why I want this is because 开发者_开发知识库I run animations that might consume quite some CPU time. When the browser tab is not visible there is no reason to continue animating. Now I know that modern browsers reduce the timer resolution of background tabs, but I could actually pause the animation, so that no CPU time whatsoever is consumed.

In case you are wondering, this is what I'm writing: http://panzi.github.com/Browser-Ponies/

At least Google Chrome supports a webkitvisibilitychange event and a document.webkitHidden property. See the visibility API. But it seems only to fire when the shown tab changes, not when the whole window is minimized. There also seems to be a visibilitychange event for Internet Explorer, but the documentation doesn't say anything about it.

The closest thing I believe you'll find is the top answer here:

Is there a way track the focus on tab with Javascript?

Now they have exactly what was needed: https://developer.mozilla.org/en-US/docs/Web/Guide/User_experience/Using_the_Page_Visibility_API