function getNode(id) {
  if (!nodeCache.hasOwnProperty(id) || !isValid(nodeCache[id], id)) {
    nodeCache[id] = ReactMount.findReactNodeByID(id);
  }
  return nodeCache[id];
}
Finds the node with the supplied React-generated DOM ID.

@param {string} id A React-generated DOM ID.
@return {DOMElement} DOM node with the suppled `id`.
@internal