This one return true if element is locate in viewport cooordinates

showElemWhileInViewport

var elementInViewport = function(elem) {
			var rect = elem.getBoundingClientRect();

			return (
				rect.top  >= 0 &&
				rect.left >= 0 &&
				rect.top  <= (window.innerHeight || document.documentElement.clientHeight)
			);
		}