js 获取当前页面的滚动位置

const getScrollPosition = (el = window) => ({
  x: el.pageXOffset !== undefined ? el.pageXOffset : el.scrollLeft,
  y: el.pageYOffset !== undefined ? el.pageYOffset : el.scrollTop
});

// 例子
getScrollPosition(); // {x: 0, y: 200}
getScrollPosition(document.getElementById('#foo')); // {x: 50, y: 100}