手写offset函数

offset函数获取距离body的左，上偏移

/*
	@params curElem 当前元素
	@return Object[{left,top}]
	@autor Tang World
*/
function offset(curElem){
  let parent = curElem.offsetParent,
      left = curElem.offsetLeft,
      top = curElem.offsetTop;
  while(parent && parent.tagName !== 'BODY') {
    left = parent.offsetLeft;
    top = parent.offsetTop;
    parent = parent.offsetParent;
  }
  return {
    left,top
	};
}

缺点:没有考虑IE8等浏览器的兼容