State and Store in frontend codebase - State example - state API

index.ts

export const decode = (apiPayload: unknown): Loaded | Failure => {
  // parse payload
  // remove admins
  // if something goes wrong, return Failure
};

export const users = (state: Loaded) => state.users;

export const addUser = (user: User.User) => (
  state: Loaded
): Loaded | Failure => {
  if (state.users.length >= 10) {
    return new Error("oops");
  }

  return {
    ...state,
    users: [...state.users, user]
  };
};

export const isLoading = (state: State): state is Loading =>  // ...
export const isError = (state: State): state is Failure => // ...

export const canCreateUser = (state: State): boolean => //...