获取页面元素的位置

var getCoords = function(el){
  var box = el.getBoundingClientRect(),
  doc = el.ownerDocument,
  body = doc.body,
  html = doc.documentElement,
  clientTop = html.clientTop || body.clientTop || 0,
  clientLeft = html.clientLeft || body.clientLeft || 0,
  top  = box.top  + (self.pageYOffset || html.scrollTop  ||  body.scrollTop ) - clientTop,
  left = box.left + (self.pageXOffset || html.scrollLeft ||  body.scrollLeft) - clientLeft
  return { 'top': top, 'left': left };
};

原文地址  https://www.cnblogs.com/rubylouvre/archive/2009/09/08/1562444.html