snap.js

window.lastScroll = 0;
	
		$(function() {
			var lastSnap, isAnimating,
				snaps = $(".snap-to"),
				$window = $(window);
			
			var heights = snaps.map(function() {
				return $(this).offset().top;
			});
			
			$window.scroll(function() {
				var closestSnap = findSnapWithin(100, $window.scrollTop() + $window.height(), snaps);

				if (closestSnap && 
						closestSnap != lastSnap &&
						!isAnimating &&
						isScrollingDown($window.scrollTop())
				) {
					
					isAnimating = true;
					lastSnap = closestSnap;
					var top = $(closestSnap).offset().top;
					
					$window.stop().scrollTo(top, 600, function() {
						isAnimating = false;
					})
				}
			});
		});
		
		function findSnapWithin(threshold, scrollTop, snaps) {
			var foundSnap = snaps.filter(function() {
				var top = $(this).offset().top;
				
				if (top < scrollTop && top > scrollTop - threshold) {
					return this;
				}
			});
			return foundSnap[0];
		}
		
		function isScrollingDown(newScroll) {
			if (newScroll > window.lastScroll) {
				window.lastScroll = newScroll;
				return true;
			} else {
				window.lastScroll = newScroll;
				return false;
			}
		}