scrollIntoView

 使当前滚动元素滚动到选中的元素区域

function scrollIntoView(container, selected) {
      if (!selected) {
        container.scrollTop = 0;
        return;
      }
      const offsetParents = [];
      let pointer = selected.offsetParent;
      while (pointer && container !== pointer && container.contains(pointer)) {
        offsetParents.push(pointer);
        pointer = pointer.offsetParent;
      }
      const top = selected.offsetTop + offsetParents.reduce((prev, curr) => (prev + curr.offsetTop), 0);
      const bottom = top + selected.offsetHeight;
      const viewRectTop = container.scrollTop;
      const viewRectBottom = viewRectTop + container.clientHeight;

      if (top < viewRectTop) {
        container.scrollTop = top;
      } else if (bottom > viewRectBottom) {
        container.scrollTop = bottom - container.clientHeight;
      }
    }