getVisibleRect(el)

Note: tests are failing, because they only run in PhantomJS on travis for now - enabling real browsers soon.

When the element is inside the viewport, getVisibleRect() returns:

{
	visibleHeight,
	visibleWidth,
	height,
	width,
	
	// these positions are relative to the elements top/left
	top,
	bottom,
	left,
	right
}

When element is outside the viewport, visibleHeight and visibleWidth will be 0, while top/bottom/left/right will be undefined.

My primary purpose for building this (and not using something else) is to calculate the visible percentage of the element. visibleHeight is actually bottom - top and visibleWidth is right - left. This means that the visible percentage is (visibleHeight * visibleWidth) / (height * width).