switchMap相關文章

• rxjs里switchMap operators的用法
• 通過rxjs的一個例子, 來學習SwitchMap的使用方法
• rxjs switchMap的實現原理
• rxjs的map和switchMap在SAP Spartacus中的應用 -將高階Observable進行flatten操作

SwitchMap can cancel in-flight network requests.

先引用rxjs官網對SwitchMap的介紹：

The main difference between switchMap and other flattening operators is the cancelling effect. On each emission the previous inner observable (the result of the function you supplied) is cancelled and the new observable is subscribed. You can remember this by the phrase switch to a new observable.

每次emission，之前的inner Observable會被cancel，新的Observable會被subscribe.

可以使用"switch to a new Observable"的方法來幫助記憶switchMap的這一特性。

Typeheads

This works perfectly for scenarios like typeaheads where you are no longer concerned with the response of the previous request when a new input arrives.

This also is a safe option in situations where a long lived inner observable could cause memory leaks, for instance if you used mergeMap with an interval and forgot to properly dispose of inner subscriptions. -

Remember, switchMap maintains only one inner subscription at a time, this can be seen clearly in the first example.

Be careful though, you probably want to avoid switchMap in scenarios where every request needs to complete, think writes to a database. switchMap could cancel a request if the source emits quickly enough. In these scenarios mergeMap is the correct option.

看個例子：

源代碼：

ngOnInit(): void {fromEvent(document, 'click').pipe(// restart counter on every clickswitchMap(() => interval(1000))).subscribe((oe) => console.log('Jerry: ' + oe));}

輸出：

switchMap的實現：

應用程序調用subscribe：

每次調用intervals函數，內部都會新建一個Observable對象：

調用了當前的next方法后，計數器加一，然后繼續在preriod毫秒后，調度下一次執行：

返回一個新的Observable對象：

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