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?

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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;