airbnb_clone/frontend/reducers/root_reducer.js

import { combineReducers } from 'redux';

import entitiesReducer from './entities_reducer';
import sessionReducer from './session_reducers';
import errorsReducer from './errors_reducer';
import uiReducer from './ui_reducer';

const rootReducer = combineReducers({
    entities: entitiesReducer,
    session: sessionReducer,
    errors: errorsReducer,
    ui: uiReducer
});

export default rootReducer;