smooth scroll AMD update

smooth-scroll.js

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

    Smooth Scroll 3.0
    Animate scrolling to anchor links, by Chris Ferdinandi.
    http://gomakethings.com

    Easing support contributed by Willem Liu.
    https://github.com/willemliu

    Easing functions forked from Gaëtan Renaudeau.
    https://gist.github.com/gre/1650294

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

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

(function(global) {

'use strict';

function smoothScrollDefinition() {

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

        // Functions to control easing
        var easingPattern = function (type, time) {
            if ( type == 'easeInQuad' ) return time * time; // accelerating from zero velocity
            if ( type == 'easeOutQuad' ) return time * (2 - time); // decelerating to zero velocity
            if ( type == 'easeInOutQuad' ) return time < 0.5 ? 2 * time * time : -1 + (4 - 2 * time) * time; // acceleration until halfway, then deceleration
            if ( type == 'easeInCubic' ) return time * time * time; // accelerating from zero velocity
            if ( type == 'easeOutCubic' ) return (--time) * time * time + 1; // decelerating to zero velocity
            if ( type == 'easeInOutCubic' ) return time < 0.5 ? 4 * time * time * time : (time - 1) * (2 * time - 2) * (2 * time - 2) + 1; // acceleration until halfway, then deceleration
            if ( type == 'easeInQuart' ) return time * time * time * time; // accelerating from zero velocity
            if ( type == 'easeOutQuart' ) return 1 - (--time) * time * time * time; // decelerating to zero velocity
            if ( type == 'easeInOutQuart' ) return time < 0.5 ? 8 * time * time * time * time : 1 - 8 * (--time) * time * time * time; // acceleration until halfway, then deceleration
            if ( type == 'easeInQuint' ) return time * time * time * time * time; // accelerating from zero velocity
            if ( type == 'easeOutQuint' ) return 1 + (--time) * time * time * time * time; // decelerating to zero velocity
            if ( type == 'easeInOutQuint' ) return time < 0.5 ? 16 * time * time * time * time * time : 1 + 16 * (--time) * time * time * time * time; // acceleration until halfway, then deceleration
            return time; // no easing, no acceleration
        };

        // Calculate how far and how fast to scroll
        // http://www.quirksmode.org/blog/archives/2008/01/using_the_assig.html
        var startLocation = window.pageYOffset;
        var endLocation = function (anchor) {
            var distance = 0;
            if (anchor.offsetParent) {
                do {
                    distance += anchor.offsetTop;
                    anchor = anchor.offsetParent;
                } while (anchor);
            }
            return distance;
        };
        var distance = endLocation(anchor) - startLocation;
        var increments = distance / (duration / 16);
        var timeLapsed = 0;
        var percentage, position, stopAnimation;

        // Scroll the page by an increment, and check if it's time to stop
        var animateScroll = function () {
            timeLapsed += 16;
            percentage = ( timeLapsed / duration );
            percentage = ( percentage > 1 ) ? 1 : percentage;
            position = startLocation + ( distance * easingPattern(easing, percentage) );
            window.scrollTo(0, position);
            stopAnimation();
        };

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

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

    }

    return smoothScroll;
}

// -------------------------- transport -------------------------- //

if ( typeof define === 'function' && define.amd ) {
    // AMD
    define( smoothScrollDefinition );
} else {
    // browser global
    global.SmoothScroll = smoothScrollDefinition();

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

        // For each smooth scroll link
        var scrollToggle = global.document.querySelectorAll('.scroll');
        [].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 = global.document.querySelector(dataID);
                var dataSpeed = toggle.getAttribute('data-speed');
                var dataEasing = toggle.getAttribute('data-easing'); // WL: Added easing attribute support.

                // If the anchor exists
                if (dataTarget) {
                    // Scroll to the anchor
                    global.SmoothScroll(dataTarget, dataSpeed || 500, dataEasing || 'easeInOutCubic');
                }

            }, false);

        });

    };

}

//TODO
// - wait for DOMReady
// - data-smoothscroll-speed / -easing
// http://www.w3.org/TR/2010/WD-html5-20101019/elements.html#embedding-custom-non-visible-data-with-the-data-attributes
// "Authors of libraries that are reused by many authors are encouraged to include their name in the attribute names,
//  to reduce the risk of clashes."
//
// - requestAnimationFrame polyfill
// https://gist.github.com/paulirish/1579671