Angular4_ Observable和subscribe

  /**
     * Registers handlers for handling emitted values,error and completions from the observable,and
     *  executes the observable's subscriber function,which will take action to set up the underlying data stream
     * @method subscribe
     * @param {PartialObserver|Function} observerOrNext (optional) either an observer defining all functions to be called,*  or the first of three possible handlers,which is the handler for each value emitted from the observable.
     * @param {Function} error (optional) a handler for a terminal event resulTing from an error. If no error handler is provided,*  the error will be thrown as unhandled
     * @param {Function} complete (optional) a handler for a terminal event resulTing from successful completion.
     * @return {ISubscription} a subscription reference to the registered handlers
     */
    subscribe(): Subscription;
    subscribe(observer: PartialObserver<T>): Subscription;
    subscribe(next?: (value: T) => void,error?: (error: any) => void,complete?: () => void): Subscription;
    protected _trySubscribe(sink: Subscriber<T>): TeardownLogic;