a native scrollTo function in javascript that uses requestAnimationFrame and easing for animation

scrollTo.js

// get element Y position
function elmYPosition(eID) {
    var elm = document.getElementById(eID),
        y = elm.offsetTop - 65,
        node = elm;
    while (node.offsetParent && node.offsetParent != document.body) {
        node = node.offsetParent;
        y += node.offsetTop;
    }
    return y;
}

// easing functions http://goo.gl/5HLl8
Math.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;
};

Math.easeInCubic = function(t, b, c, d) {
    var tc = (t /= d) * t * t;
    return b + c * (tc);
};

Math.inOutQuintic = function(t, b, c, d) {
    var ts = (t /= d) * t,
        tc = ts * t;
    return b + c * (6 * tc * ts + -15 * ts * ts + 10 * tc);
};

// requestAnimationFrame for Smart Animating http://goo.gl/sx5sts
var requestAnimFrame = (function() {
    return window.requestAnimationFrame || window.webkitRequestAnimationFrame || window.mozRequestAnimationFrame || function(callback) {
        window.setTimeout(callback, 1000 / 60);
    };
})();


/**
 * @param {string} the ID of the element you would like to scroll to
 * @param {int} optional integer for duration of scroll, defaults to 500ms
 * @param {object} optional options object for callback
 * @param {function} optional callback function
 */

function scrollTo(eID, duration, options, callback) {
    if (typeof options === 'undefined') {
        options = {};
    }

    // because it's so fucking difficult to detect the scrolling element, just move them all
    function move(amount) {
        document.documentElement.scrollTop = amount;
        document.body.parentNode.scrollTop = amount;
        document.body.scrollTop = amount;
    }

    function position() {
        return document.documentElement.scrollTop || document.body.parentNode.scrollTop || document.body.scrollTop;
    }
    var start = position(),
        to = elmYPosition(eID),
        change = to - start,
        currentTime = 0,
        increment = 20;
    duration = (typeof(duration) === 'undefined') ? 500 : duration;
    var animateScroll = function() {
        // increment the time
        currentTime += increment;
        // find the value with the quadratic in-out easing function
        var val = Math.easeInOutQuad(currentTime, start, change, duration);
        // move the document.body
        move(val);
        // do the animation unless its over
        if (currentTime < duration) {
            requestAnimFrame(animateScroll);
        } else {
            if (callback && typeof(callback) === 'function') {
                // the animation is done so lets callback
                callback(options);
            }
        }
    };
    animateScroll();
}