combine-reducers.js

let initialState = {
  one: 'two',
  three: 'four'
}
function update1 (state = initialState, action) {
  
  switch (action.type) {
    
    case SOMETHING: {
      return state.one = 'changed'
    }
    
    default: {
      return state;
    }
  }
}

function update2 (state, action) {
  
  // etc.
}

let rootUpdate = combineReducers({
  update1: update1, // update1.one and update1.three
  update2: update2
})