• Only gives the distance between the element and it’s nearest “offsetParent” (which is the element that controls it’s position).
• If you have an element with position: absolute and top: 100 and it has a child that flows naturally to 100px within it, the offsetTop of that element will be 100, not 200 as you might expect.

There are really 2 ways to get the position of an element from the top/left of the body/document.

1. window.pageXOffset + element.getBoundingClientRect().left (switch for pageYOffset and .top for vertical)
2. Iterate through offset parents:

function getTop(element) {
  var y = 0;
  while (element != null && element != document.body) {
    y += element.offsetTop;
    element = element.offsetParent;
  }
  return y;
}
// substitute offsetLeft for horizontal