helperFunctions.js

var helperFunctions = (function () {
	return {
		isSectionInViewport: function (el) {
			const scrollPosition = window.pageYOffset || document.documentElement.scrollTop;
			var top = el.offsetTop;
			var left = el.offsetLeft;
			var width = el.offsetWidth;
			var height = el.offsetHeight;

			while (el.offsetParent) {
				el = el.offsetParent;
				top += el.offsetTop;
				left += el.offsetLeft;
			}

			return (
				top < (scrollPosition + window.innerHeight) &&
				(top + height) > scrollPosition
			);
		},
		scrollDirection: function (scrollPosition, lastScrollPosition, orientation = 'vertical') {
			var direction = '';
			if (orientation !== 'horizontal') {
				if (scrollPosition > lastScrollPosition) {
					direction = 'down';
				} else {
					direction = 'up';
				}
			} else {
				if (scrollPosition > lastScrollPosition) {
					direction = 'right';
				} else {
					direction = 'left';
				}
			}
			return direction;
		},
		centerOffset: function (el) {
			return el.offsetLeft + (el.clientWidth / 2) - (window.innerWidth / 2);
		},
		swipeDetectv2: function (el, handleSwipe) {
			var xDown = null,
				yDown = null;

			function getTouches(evt) {
				return evt.touches;
			}

			function handleTouchStart(evt) {
				const firstTouch = getTouches(evt)[0];
				xDown = firstTouch.clientX;
				yDown = firstTouch.clientY;
			};

			function handleTouchMove(evt) {
				if (!xDown || !yDown) return;

				var xUp = evt.touches[0].clientX;
				var xDiff = xDown - xUp;

				var yUp = evt.touches[0].clientY;
				var yDiff = yDown - yUp;

				if (Math.abs(xDiff) > Math.abs(yDiff)) {
					/*most significant*/
					if (xDiff > 0) {
						handleSwipe('left');
					} else {
						handleSwipe('right');
					}
				} else {
					if (yDiff > 0) {
						/* up swipe */
						handleSwipe('up');
					} else {
						/* down swipe */
						handleSwipe('down');
					}
				}
				/* reset values */
				xDown = null;
				yDown = null;
			};

			function enable() {
				el.addEventListener('touchstart', handleTouchStart, false);
				el.addEventListener('touchmove', handleTouchMove, false);
			}

			function destroy() {
				el.removeEventListener('touchstart', handleTouchStart, false);
				el.removeEventListener('touchmove', handleTouchMove, false);
			}

			return {
				enable: enable,
				destroy: destroy
			}
		}
	}
}());