function isInViewportRange( elementStart, elementEnd ) {
	let viewportStart = window.scrollY,
		viewportEnd = document.documentElement.clientHeight + window.scrollY;
	return elementStart > viewportStart && elementEnd < viewportEnd;
}
function isInViewportRange( elementStart, elementEnd ) {
	let viewportStart = window.scrollY,
		viewportEnd = document.documentElement.clientHeight + window.scrollY;
	return elementStart > viewportStart && elementEnd < viewportEnd;
}
function isInViewportRange ( elementStart , elementEnd ) { let viewportStart = window . scrollY , viewportEnd = document . documentElement . clientHeight + window . scrollY ; return elementStart > viewportStart && elementEnd < viewportEnd ; }
Checks whether the given bounds are within the viewport
@param {number} elementStart
@param {number} elementEnd
@returns {boolean}
Checks whether the given bounds are within the viewport