code: function commonAncestor(nodeA, nodeB) {
    const ancestors = listAncestor(nodeA);
    for (let n = nodeB; n; n = n.parentNode) {
      if (ancestors.indexOf(n) > -1) return n;
    }
    return null; // difference document area
  }
docs: returns common ancestor node between two nodes.
  
  @param {Node} nodeA
  @param {Node} nodeB