关于rxjs：使用scan Observable返回默认值

Return a default value with scan Observable

我可以阅读rxjs文档(http://reactivex.io/rxjs/class/es6/Observable.js~Observable.html#instance-method-scan)中有关方法扫描的观点。

在下面的代码中，我想返回_channels Observables的默认值。

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export interface IChannelOperation extends Function {
(channels: Channel[]): Channel[];
}
let initialChannel: Channel[] = [];

@Injectable()
export class ChannelsCatalog{
defaultChannel: Subject<Channel> = new BehaviorSubject<Channel>(null);

private _currentChannel: Subject<Channel> = new BehaviorSubject<Channel>(null);
private _channels: Observable<Channel[]>;

private _updates: Subject = new Subject();

constructor(){
this._channels = this._updates
.scan((channels: Channel[], operation: IChannelOperation) => operation(channels), initialChannel)
.publishReplay(1)
.refCount();
}

getAllChannelsCatalog(): Observable<Channel[]>{
return this._channels;
}
}

但是，当我订阅可观察的ex时，seed参数不会返回：

1 2	var channelsCatalog = new ChannelsCatolog(); channelsCatalog.getAllChannelsCatalog.subscribe((value) => console.log(value));