使用 concatMap 时如何取消订阅 valueChanges？

Question

I'm reading an article about the rxjs concatMap operator. This guy builds an autosave form, ie, whenever the user types a letter the data is saved using a http request

this.subscription = this.form.valueChanges
      .pipe(concatMap(formValue => this.http.put(`/api/course/${courseId}`, formValue)))
      .subscribe(saveResult =>  ... handle successful save ...);

I want to be able to unsubscribe in ngOnDestroy() from the valueChanges Observable, but the this.subscription Subscription refers to the http observable. So how can I unsubscribe from valueChanges ?

Answer 1

In your ngOnDestroy function simply use your reference to the subscription. When you create the observable it returns back a subscription object which exposes the unsubscribe() method.

ngOnDestroy{
this.subscription.unsubscribe();
}