redux-03.js

/*
expected state:

{
  accounts: {
    items: []
    isFetching: boolean
    fetchingErrorMessage: string
  }
}
*/

// accountReducers.js

function accounts() {}
function isFetching() {}
function fetchingErrorMessage() {}

export default combineReducers({
  items: accounts,
  isFetching,
  fetchingErrorMessage
}); 

//combineReducers is from react-redux library, result is the same as here:

export default function (state = {}, action) {
  return {
    items: accounts(state.accounts.items, action),
    isFetching: isFetching(state.accounts.isFetching, action),
    fetchingErrorMessage: fetchingErroMessage(state.accounts.fetchingErrorMessage, action)
  };
}

// rootReducer.js
// import accountReducers from "accountReducers.js"

export default combineReducers({
  accounts: accountReducers
});