Remove complexity from redux reducers

complexityReducer.js

const initialObjectivesState = {
    aString: '',
};

/*
 * As the number of actions increases, the cyclomatic complexity of the reducer will skyrocket
 */
const Reducer = function (state = initialObjectivesState, action) {
  switch(action.type){
    "UPDATE_STRING": function(state, action){
      return {
        ...state,
        aString: action.value,
      };
    };
    default: return state;
  }
};

export default Reducer;

reducer.js

const initialObjectivesState = {
    aString: '',
};

const actionMap = {
  "UPDATE_STRING": function(state, action){
    return {
      ...state,
      aString: action.value,
    };
  }
};


const Reducer = function (state = initialObjectivesState, action) {
    if(actionMap[action.type]){
        return actionMap[action.type](state, action);
    } else {
        return state;
    }
};

export default Reducer;