how to determin if the current browser is in fullscreen mode in opera mobile

How in Javascript can we tell if the current browser is in fullscreen mode? is there an exact ratio of width/height i can depend on to measure this? Im hoping to have that info for Opera Mobile since it acts odd when it goes in full screen, it doesnt auto hid开发者_如何学Ce the small buttons at the bottom which means part of my bottom navigation is hidden away!

I would check whether the user's resolution and viewport are within 30px or so. Measure the full screen chrome and minus that from the resolution to see if the viewport size is similar.

That is just a guess and not reliable.