Determine whether webpage has foreground window focus/is active tab?

I'd like to be able to mute activity of my app if I can detect that the page is no longer focused. For instance, if the page is in a background tab or another app has focus, I'd like to disable a constantly polling script or switch modal notifications to the new HTML5 notifications API.

Is there any way to get this with JS, and 开发者_JAVA技巧if so, which browsers are supported?

PS - I've seen this, but don't know if it would work for what I'm looking to do. Anybody have any insight?

You can listen for the blur event on your window, then for when the user comes back, you can use the focus event:

Here's an example in jQuery:

$(window).blur(disableStuff).focus(enableStuff);

Or in pure JavaScript:

window.onblur = disableStuff;
window.onfocus = enableStuff;