stateGenerator.js

// Create store accepts reducers map and initial state
function* createStore(reducers, initialState = {}) {
  // Initialize state
  let state = initialState;
  // Extract the reducer keys upfront
  const reducerKeys = Object.keys(reducers);
  // Combine all reducers into one reducing function
  const combinedReducer = (state, action) => {
    return reducerKeys.reduce((newState, key) => {
      // Pass slice of state into corresponding reducer
      newState[key] = reducers[key](state[key], action); 
      return newState;
    }, {});
  }

  // Generator loop handles each action
  while (true) {
    // Yield current state and wait for next action
    const action = yield state;
    // Pass current state and action to combined reducer
    if (action) state = combinedReducer(state, action);
  }
}

// Reducer example
function usersReducer(state = {}, action) {
  // Reducer logic to update state immutably
  // based on action.type
}

// Create reducers map with slice reducers
const reducers = {
  users: usersReducer
};

// Initialize store with reducers (and optional initial state)
const store = createStore(reducers);

// Dispatch actions to trigger state updates, get value
store.next({type: 'ADD_USER'}).value;