function getScope(node, key) {
  if (!key) {
    return node;
  }
  const keys = key.split('.');
  for (let i = 0, n = keys.length; i < n; ++i) {
    const k = keys[i];
    node = node[k] || (node[k] = Object.create(null));
  }
  return node;
}
@param {object} node
@param {string} key
@return {object}