excerpt of router.ts demonstrating how switchMap is used to cancel and cleanup pending navigations

router.ts

private setupNavigations(transitions: Observable<NavigationTransition>): Observable<NavigationTransition> {
    return transitions.pipe(
        filter(t => t.id !== 0),
        // Extract URL
        map(t => ({...t, extractedUrl: this.urlHandlingStrategy.extract(t.rawUrl)}) as NavigationTransition),
         // Using switchMap so we cancel executing navigations when a new one comes in
        switchMap(t => {