yip

angular2-rxjs.ts

public ngOnInit() {
    this.navigationResults = this.helpDataService.getMainGroups()
      .concat(this.filterBox.valueChanges
        .let((text: Observable<string>) => this.filterAndDebounceFor(text)(500))
        .switchMap((filterTerm: string) =>
          this.defaultObservableIfEmpty(
            this.helpDataService.getNavigationByFilter(filterTerm),
            this.helpDataService.getMainGroups())));
  }

  private filterAndDebounceFor = (input: Observable<string>) => {
    return (delay: number) => input
      .filter((text: string) => text.length > 2 || text.length === 0)
      .debounceTime(delay);
  }

  private defaultObservableIfEmpty = (current: Observable<any>, fallback: Observable<any>) => {
    return current.publish((source: Observable<any>) =>
      source.merge(source.isEmpty().filter((e: boolean) => e).mergeMapTo(fallback)));
  }