function nodeIsEmpty(gltf, nodeId, usedNodeIds) {
  const node = gltf.nodes[nodeId];
  if (
    defined(node.mesh) ||
    defined(node.camera) ||
    defined(node.skin) ||
    defined(node.weights) ||
    defined(node.extras) ||
    (defined(node.extensions) && Object.keys(node.extensions).length !== 0) ||
    defined(usedNodeIds[nodeId])
  ) {
    return false;
  }

  // Empty if no children or children are all empty nodes
  return (
    !defined(node.children) ||
    node.children.filter(function (n) {
      return !nodeIsEmpty(gltf, n, usedNodeIds);
    }).length === 0
  );
}
Contains functions for getting a list of element ids in use by the glTF asset.
@constructor

@private