RxJS problem

search-box.ts

languageChangedSubscription = this.languageService.languageChanged
      .subscribe((language: string) => {
        this.updateViewData(language);
      });

updateViewData(language: string) {
    this.searchResults = this.searchBox.valueChanges
      .let((text: Observable<string>) => this.filterAndDebounceFor(text)(150))
      .switchMap((searchTerm: string) => this.helpDataService.search(searchTerm, language));
  }