usage example:

const saveGameData = new SaveGame(); // make a custom schema for saved games data
... /* add all state objects from your game manager to saveGameData */
const serialized = await schemaToString(saveGameData);
... /* save to file, read from file etc. */
const loadedGameData: SaveGame = await stringToSchema(SaveGame, serialized );
... /* take game state object from loadedGameData into your game manager */

see code in this gist