root.reducer.ts

import {ActionReducer, ActionReducerMap, MetaReducer} from '@ngrx/store';
import {State} from './root.state';
import {environment} from '../../environments/environment';

export const rootReducers: ActionReducerMap<State> = {
  // YOUR REDUCERS HERE
};


export const rootMetaReducers: MetaReducer<State>[] = [];

if (environment.hmr) {
  rootMetaReducers.push((reducer: ActionReducer<any>): ActionReducer<any> => {
    return function (state: any, action: any) {
      if (action.type === 'SET_ROOT_STATE') {
        return action.payload;
      }
      return reducer(state, action);
    };
  });
}

Updated ;)