获取元素距离顶部的距离

这个方法太常用了，写个笔记

 //获取顶部距离
function getTop(element) {
  let realTop = element.offsetTop;
  let parent = element.offsetParent;
  while (parent !== null) {
  realTop += parent.offsetTop;
  parent = parent.offsetParent;
  }
  return realTop;
},

接收原生dom对象