Easiest way to detect direction of drag

gistfile1.txt

var dragStartX;
var dragStartY;

window.addEventListener("dragstart",function(e){
  dragStartX = Math.ceil(e.offsetX/70);
  dragStartY = Math.ceil(e.offsetY/70);
})

window.addEventListener("dragend",function(e){
  var dropX = Math.abs(dragstartX - e.screenX);
  var dropY = Math.abs(dragstartY - e.screenY);
  if(dropX  > dropY){
    // Direction is X
  }else if(dropX < dropY){
    // direction is Y;
  }
});