smooth-scroll.js

/* =============================================================

	Smooth Scroll 2.3
	Animate scrolling to anchor links, by Chris Ferdinandi.
	http://gomakethings.com

	Free to use under the MIT License.
	http://gomakethings.com/mit/

 * ============================================================= */

 (function() {

	'use strict';

	// Feature Test
	if ( 'querySelector' in document && 'addEventListener' in window && Array.prototype.forEach ) {

		// Function to animate the scroll
		var smoothScroll = function (anchor, duration) {

			// Calculate how far and how fast to scroll
			var startLocation = window.pageYOffset;
			var endLocation = anchor.offsetTop;
			var distance = endLocation - startLocation;
			var increments = distance/(duration/16);
			var stopAnimation;

			// Scroll the page by an increment, and check if it's time to stop
			var animateScroll = function () {
				window.scrollBy(0, increments);
				stopAnimation();
			};

			// If scrolling down
			if ( increments >= 0 ) {
				// Stop animation when you reach the anchor OR the bottom of the page
				stopAnimation = function () {
					var travelled = window.pageYOffset;
					if ( (travelled >= (endLocation - increments)) || ((window.innerHeight + travelled) >= document.body.offsetHeight) ) {
						clearInterval(runAnimation);
					}
				};
			}
			// If scrolling up
			else {
				// Stop animation when you reach the anchor OR the top of the page
				stopAnimation = function () {
					var travelled = window.pageYOffset;
					if ( travelled <= (endLocation || 0) ) {
						clearInterval(runAnimation);
					}
				};
			}

			// Loop the animation function
			var runAnimation = setInterval(animateScroll, 16);

		};

		// Define smooth scroll links
		var scrollToggle = document.querySelectorAll('.scroll');

		// For each smooth scroll link
		[].forEach.call(scrollToggle, function (toggle) {

			// When the smooth scroll link is clicked
			toggle.addEventListener('click', function(e) {

				// Prevent the default link behavior
				e.preventDefault();

				// Get anchor link and calculate distance from the top
				var dataID = toggle.getAttribute('href');
				var dataTarget = document.querySelector(dataID);
				var dataSpeed = toggle.getAttribute('data-speed');

				// If the anchor exists
				if (dataTarget) {
					// Scroll to the anchor
					smoothScroll(dataTarget, dataSpeed || 500);
				}

			}, false);

		});

	}

 })();