silverstripe-framework/admin/client/src/state/config/ConfigReducer.js

import deepFreeze from 'deep-freeze-strict';
import ACTION_TYPES from './ConfigActionTypes';

function configReducer(state = {}, action) {
  switch (action.type) {

    case ACTION_TYPES.SET_CONFIG:
      return deepFreeze(Object.assign({}, state, action.payload.config));

    default:
      return state;

  }
}

export default configReducer;