js 判断一个元素是否包含另一个元素

// contains 实现
const contains = (root, el) => {
  if (root.compareDocumentPosition)
    return root === el || !!(root.compareDocumentPosition(el) & 16);
  if (root.contains && el.nodeType === 1){
    return root.contains(el) && root !== el;
  }
  while ((el = el.parentNode))
    if (el === root) return true;
  return false;
}