That's exactly what it's doing -- it's trying to figure out if your viewport is looking at the content 'above the fold', so that it can show the "splash iframe"

That's exactly what it's doing -- it's trying to figure out if your viewport is looking at the content 'above the fold', so that it can show the "splash iframe" [1] while you're looking at it, and stop JS-animating it when you're not. [1] http://ncase.me/ballot/splash/splash.html http://ncase.me/ballot/splash/splash.html