Does JavaScript execute when the application is in the background?

Question

Suppose I have a site with simple javascript:

t = setInterval( callback, 30*1000 ); var callback = function() { document.write('foobar'); }; 

If a user visits my site from a mobile device, I wonder if the callback will continue to execute after the page / application is in the background. I know that all mobile devices do not match, so for clarity, you can define some specific scenarios:

• IOS device using Mobile Safari
• IOS device using a native UIWebView app
• Android device in default web application
• Android device using native application with WebView

In what case (if any) of these cases will the user return in an hour to the screen full of foobar s?

Update

5. iOS 8+ (just released while writing this) according to this guy :

Now JavaScript continues to execute, even being an inactive tab (timers slow down to 1 s) and even safari to the background.