library.js

const useApi = (apiFactory, initialState) => {
  let [state, setState] = useState(initialState);
  return useMemo(() => apiFactory({ state, setState }), [
    state,
    setState,
    apiFactory
  ]);
};

const createStore = (apiFactory, initialState) => {
  const StoreContext = createContext();

  const StoreProvider = props => {
    let store = useApi(apiFactory, initialState);
    return (
      <StoreContext.Provider value={store}>
        {props.children}
      </StoreContext.Provider>
    );
  };

  let useStore = () => {
    return useContext(StoreContext);
  };

  return [StoreProvider, useStore];
};

const createTestApi = (apiFactory, defaultValue) => {
  let state = defaultValue;
  let setState = updater => {
    if (typeof updater === "function") {
      state = updater(state);
    } else {
      state = updater;
    }
    ref.api = apiFactory({ state, setState });
  };
  let ref = {
    api: apiFactory({ state, setState })
  };
  return ref;
};