pause offscreen

On web pages, hide gifs and pause videos when they're scrolled offscreen, to save CPU cycles.

var pauser = require('pause-offscreen')
var unlistenPauser = pauser(containerEl)
ui.onTeardown(unlistenPauser)

Notes

• Only bothers checking vertical scroll position
• Does not check if the page is visible (just checks if the element is in the viewport)
• Shows/hides on initial call, then on scroll
• Hides all images when they go out of viewport (visibility=hidden) because my usecase couldnt use the filename's extension to differentiate gifs from other images.