TypeScript operators.startWith函數代碼示例

 public initialize() {
   return {
     view: {
       base: this.intent.test().pipe(
         scan((acc, next: any) => acc + 1, 1),
         share(),
         startWith(1),
       ),
       test: this.intent.test().pipe(
         scan((acc, next: any) => acc + 1, 1),
         share(),
         startWith(1),
       ),
       test2: this.subject.pipe(
         map(({ type, payload, states }) => {
           switch (type) {
             case 'subject-test':
               return payload + states.test2;
             default:
               return payload;
           }
         }),
         startWith(1),
       ),
     },
   };
 }

  it('should convert observable obeject to ordinal object', done => {
    const aValue = new Subject();
    const bValue = new Subject();
    const BUFFER_COUNT = 4;

    const values = createObject(
      aValue.pipe(startWith('')),
      bValue.pipe(startWith('')),
    );

    subscription.add(
      combineTemplate(values)
        .pipe(bufferCount(BUFFER_COUNT))
        .subscribe(v => {
          /*tslint:disable:no-magic-numbers*/
          expect(v[0]).to.be.deep.eq(createObject('', ''));
          expect(v[1]).to.be.deep.eq(createObject('200', ''));
          expect(v[2]).to.be.deep.eq(createObject('200', '300'));
          expect(v[3]).to.be.deep.eq(createObject('OK', '300'));
          /*tslint:enable:no-magic-numbers*/
          done();
        }),
    );

    aValue.next('200');
    bValue.next('300');
    aValue.next('OK');
  });

 /**
  * Creates an observable list of recently opened apps
  * @param {number} max
  * @returns {Observable<any[]>}
  */
 getRecentApps(max = 20): Observable<RecentAppTab[]> {
     return combineLatest(
         this.localRepository.getRecentApps().pipe(
             startWith([])
         ),
         this.platformRepository.getRecentApps().pipe(
             map(apps => apps || []),
             startWith([])
         ), (localApps, platformApps) => [...localApps, ...platformApps].sort((a, b) => b.time - a.time).slice(0, max)
     );
 }

export function sampleObservable(obs: Observable<any>, scheduler?: any) {
  return obs.pipe(
    sampleTime(100, scheduler),
    share(),
    startWith('')
  );
}

 cascade =>
     isErrorLike(cascade.final)
         ? [cascade.final]
         : queryConfiguredExtensions({ queryGraphQL }, cascade).pipe(
               catchError(error => [asError(error) as ErrorLike]),
               startWith(LOADING)
           )

 return Object.keys(apps).reduce((states, key) => {
   const app = apps[key];
   const nextState = app(subject, initialState[key]);
   if (nextState.view) {
     if (!isObservable(nextState.view)) {
       throw new Error(`Application view of ${key} must be Observable.`);
     }
     nextState.view = nextState.view.pipe(startWith(initialState[key]));
     if (!states.view) {
       states.view = {};
     }
     if (!isDefined(states.view[key])) {
       states.view[key] = nextState.view;
     } else {
       states.view[key] = merge(states.view[key], nextState.view);
     }
   }
   for (const key in nextState) {
     if (key !== 'view') {
       if (!nextState[key] || !(nextState[key] instanceof Observable)) {
         throw new Error(`Property ${key} must be Observable.`);
       }
       if (states[key]) {
         states[key] = merge(states[key], nextState[key]);
       } else {
         states[key] = nextState[key];
       }
     }
   }
   return states;
 }, states);

  function addLoadingCount(count$: Observable<number>) {
    count$
      .pipe(
        distinctUntilChanged(),

        tap(count => {
          if (count < 0) {
            throw new Error(
              'Observables passed to loadingCount.add() must only emit positive numbers'
            );
          }
        }),

        // use takeUntil() so that we can finish each stream on stop() the same way we do when they complete,
        // by removing the previous count from the total
        takeUntil(stop$),
        endWith(0),
        startWith(0),
        pairwise(),
        map(([prev, next]) => next - prev)
      )
      .subscribe({
        next: delta => {
          loadingCount$.next(loadingCount$.getValue() + delta);
        },
        error: error => {
          if (fatalErrors) {
            fatalErrors.add(error);
          }
        },
      });
  }

    ngOnInit () {
        this.playlist$ = this._route.paramMap.pipe(
            map(paramMap => ({ playlistId: paramMap.get('id'), playlistOwnerId: paramMap.get('user') })),
            switchMap(params =>
                this._spotifyService.getPlaylist(params.playlistOwnerId, params.playlistId)
            ),
            map(playlist => ({
                isLoading: false,
                result: playlist
            })),
            startWith({
                isLoading: true,
                result: null
            }),
            shareReplay()
        );

        this.tracks$ = this.playlist$.pipe(
            filter(o => !o.isLoading && !!o.result),
            map(o => o.result.Tracks)
        );

        this.playlistUrl$ = this.playlist$.pipe(
            filter(o => !o.isLoading && !!o.result),
            map(o => o.result),
            map(playlist => playlist.ImageUrls.length ? playlist.ImageUrls[0] : '')
        );
    }

export function canExecuteFromNgForm(form: AbstractControl | AbstractControlDirective): Observable<boolean> {
	return form.statusChanges!.pipe(
		startWith(form.valid),
		map(() => !!form.valid),
		distinctUntilChanged(),
	);
}

 function app(sources: any): any {
   return {
     other: sources.other.pipe(
       take(1),
       startWith('a')
     ),
   };
 }