• metaReducer 是 Action -> Reducer 之间的钩子，允许开发者对 Action 进行预处理 (在普通 Reducer 函数调用之前调用) ```typescript function debug(reducer: ActionReducer): ActionReducer { return function (state, action) { return reducer(state, action) } }

    export const metaReducers: MetaReducer[] = !environment.production ? [debug] : [] ```