当使用Local storage来存储NGRX状态时，我们需要确保状态是immutable（不可变的）的。原因是我们需要在每次更新状态时创建一个新的对象，以便在存储状态时避免出现任何类型的副作用。 以下是在Angular中保存NGRX状态的示例代码：

import { Action, ActionReducer, MetaReducer } from '@ngrx/store';

export function localStorageSyncReducer(reducer: ActionReducer): ActionReducer {
  return (state: any, action: Action): any => {
    const nextState = reducer(state, action);
    const serializedState = JSON.stringify(nextState);
    localStorage.setItem('state', serializedState);
    return nextState;
  };
}

export function localStorageSyncReducerFactory(reducer: ActionReducer): ActionReducer {
  return localStorageSyncReducer(reducer);
}

export const metaReducers: MetaReducer[] = [localStorageSyncReducerFactory];

此代码使用localStorageSyncReducer作为一个高阶reducer来处理同步操作并将状态存储在Local storage中。 在应用程序启动时，您可以通过检查Local storage中的值来还原状态，如下所示：

export function getInitialState() {
  const serializedState = localStorage.getItem('state');
  if (serializedState === null) {
    return undefined;
  } else {
    return JSON.parse(serializedState);
  }
}

@NgModule({
  imports: [
    ...
    StoreModule.forRoot(reducers, { initialState: getInitialState }),
    ...
  ],
  ...
})
export class AppModule { }

以上是使用Local storage在Angular中保存NGRX状态的完整示例。