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