Animated scrolling without any dependency on libraries. If user scrolls when animation is running, scroll animation would be immediately canceled.

animatedScrollTo.js

window.requestAnimFrame = (function(){return window.requestAnimationFrame||window.webkitRequestAnimationFrame||window.mozRequestAnimationFrame||function(callback){window.setTimeout(callback,1000/60);};})();

var easeInOutQuad = function (t, b, c, d) {
    t /= d/2;
    if (t < 1) return c/2*t*t + b;
    t--;
    return -c/2 * (t*(t-2) - 1) + b;
};

var animatedScrollTo = function (element, to, duration) {
    var start = element.scrollTop,
    change = to - start,
    animationStart = +new Date();
    var animating = true;
    var lastpos = null;

    var animateScroll = function() {
        if (!animating) {
            return;
        }
        requestAnimFrame(animateScroll);
        var now = +new Date();
        var val = Math.floor(easeInOutQuad(now - animationStart, start, change, duration));
        if (lastpos) {
            if (lastpos === element.scrollTop) {
                lastpos = val;
                element.scrollTop = val;
            } else {
                animating = false;
            }
        } else {
            lastpos = val;
            element.scrollTop = val;
        }
        if (now > animationStart + duration) {
            element.scrollTop = to;
            animating = false;
        }
    };
    requestAnimFrame(animateScroll);
};

example.js

// scroll to top in 10 seconds

button.addEventListener('click', function () {
    animatedScrollTo(document.body, 0, 10000);
});