getOffset.js

// Get element offset from top of page
function getOffset(el) {
  el = el.getBoundingClientRect();
  return {
    left: el.left + window.scrollX,
    top: el.top + window.scrollY
  };
};

scrollTo.js

// Scroll element to a integer position
function scrollTo(element, to, duration) {
  if (duration <= 0) return;
  var difference = to - element.scrollTop;
  var perTick = difference / duration * 10;

  setTimeout(function() {
    element.scrollTop = element.scrollTop + perTick;
    if (element.scrollTop === to) return;
    scrollTo(element, to, duration - 10);
  }, 10);
};