我对这个问题有自己的看法，但最好仔细检查并确定。感谢您的关注并尝试提供帮助。这里是：
想象一下，我们正在调度一个动作，该动作触发了一些状态变化，并且还附加了一些效果。所以我们的代码必须做两件事——改变状态和做一些副作用。但是这些任务的顺序是什么？我们是否同步进行？我相信首先，我们改变状态然后做副作用，但是有没有可能，这两个任务之间可能会发生其他事情？像这样：我们改变状态，然后得到一些我们之前做的 HTTP 请求的响应并处理它，然后做副作用。
[编辑：] 我决定在这里添加一些代码。我也简化了很多。
状态：
export interface ApplicationState {
loadingItemId: string;
items: {[itemId: string]: ItemModel}
}
行动：
export class FetchItemAction implements Action {
readonly type = 'FETCH_ITEM';
constructor(public payload: string) {}
}
export class FetchItemSuccessAction implements Action {
readonly type = 'FETCH_ITEM_SUCCESS';
constructor(public payload: ItemModel) {}
}
减速器：
export function reducer(state: ApplicationState, action: any) {
const newState = _.cloneDeep(state);
switch(action.type) {
case 'FETCH_ITEM':
newState.loadingItemId = action.payload;
return newState;
case 'FETCH_ITEM_SUCCESS':
newState.items[newState.loadingItemId] = action.payload;
newState.loadingItemId = null;
return newState;
default:
return state;
}
}
影响：
@Effect()
FetchItemAction$: Observable<Action> = this.actions$
.ofType('FETCH_ITEM')
.switchMap((action: FetchItemAction) => this.httpService.fetchItem(action.payload))
.map((item: ItemModel) => new FetchItemSuccessAction(item));
这就是我们调度 FetchItemAction 的方式：
export class ItemComponent {
item$: Observable<ItemModel>;
itemId$: Observable<string>;
constructor(private route: ActivatedRoute,
private store: Store<ApplicationState>) {
this.itemId$ = this.route.params.map(params => params.itemId);
itemId$.subscribe(itemId => this.store.dispatch(new FetchItemAction(itemId)));
this.item$ = this.store.select(state => state.items)
.combineLatest(itemId$)
.map(([items, itemId]: [{[itemId: string]: ItemModel}]) => items[itemId])
}
}
期望的场景：
User clicks on itemUrl_1;
we store itemId_1 as loadingItemId;
make the request_1;
user clicks on itemUrl_2;
we store itemId_2 as loadingItemId;
switchMap operator in our effect cancells previous request_1 and makes request_2;
get the item_2 in response;
store it under key itemId_2 and make loadingItemId = null.
糟糕的场景：
User clicks on itemUrl_1;
we store itemId_1 as loadingItemId;
make the request_1;
user clicks on itemUrl_2;
we store itemId_2 as loadingItemId;
we receive the response_1 before we made the new request_2 but after loadingItemId changed;
we store the item_1 from the response_1 under the key itemId_2;
make loadingItemId = null;
only here our effect works and we make request_2;
get item_2 in the response_2;
try to store it under key null and get an error
所以问题很简单，糟糕的情况是否真的会发生？
