code: function default_deduplicator(objectA, objectB) {
    // default deduplication handler:
    // if object versions differ, use highest available version
    if ((objectA.version || objectB.version) &&
        (objectA.version !== objectB.version)) {
      return (+objectA.version || 0) > (+objectB.version || 0)
        ? objectA
        : objectB;
    }
    // otherwise: return merged obj properties
    return _.merge(objectA, objectB);
  }
docs: default deduplication helper function