using.js

  var UsingObservable = (function (__super__) {
    inherits(UsingObservable, __super__);
    function UsingObservable(resFn, obsFn) {
      this._resFn = resFn;
      this._obsFn = obsFn;
      __super__.call(this);
    }

    UsingObservable.prototype.subscribeCore = function (o) {
      var disposable = disposableEmpty;
      var resource = tryCatch(this._resFn)();
      if (resource === errorObj) {
        return new BinaryDisposable(observableThrow(resource.e).subscribe(o), disposable);
      }
      resource && (disposable = resource);
      var source = tryCatch(this._obsFn)(resource);
      if (source === errorObj) {
        return new BinaryDisposable(observableThrow(source.e).subscribe(o), disposable);
      }
      return new BinaryDisposable(source.subscribe(o), disposable);
    };

    return UsingObservable;
  }(ObservableBase));

  /**
   * Constructs an observable sequence that depends on a resource object, whose lifetime is tied to the resulting observable sequence's lifetime.
   * @param {Function} resourceFactory Factory function to obtain a resource object.
   * @param {Function} observableFactory Factory function to obtain an observable sequence that depends on the obtained resource.
   * @returns {Observable} An observable sequence whose lifetime controls the lifetime of the dependent resource object.
   */
  Observable.using = function (resourceFactory, observableFactory) {
    return new UsingObservable(resourceFactory, observableFactory);
  };