scrollTo.js

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

function scrollTo(element, to, duration, easing, callback) {
  // figure out if this is moz || IE because they use documentElement
  element = (typeof(element) === 'undefined' ? ((navigator.userAgent.indexOf('Firefox') != -1 || navigator.userAgent.indexOf('MSIE') != -1) ? document.documentElement : document.body): element);
  easing = (typeof(easing) !== 'function' ? Math.easeInOutQuad: easing);
  duration = (typeof(duration) === 'undefined' ? 500: duration);
  var start = element.scrollTop,
  change = to - start,
  currentTime = 0,
  frames = 0,
  lastTime = Date.now();
  var animateScroll = function(){
    // increment the time
    currentTime = Date.now() - lastTime;
    // find the value with the quadratic in-out easing function
    var val = easing(currentTime, start, change, duration);
    // move the document.body
    element.scrollTop = val;
    // do the animation unless its over
    if(currentTime < duration) {
      frames++;
      requestAnimFrame(animateScroll);
    } else {
      if (callback && typeof(callback) === 'function') {
        // the animation is done so lets callback
        callback();
      }
      console.debug("[scrollTo] drew " + frames.toString(10) + " frames in " + (Date.now() - startTime).toString(10) + "ms");
    }
  };
  animateScroll();
}