_url(name: string): string {
    const projectId = this.app_.options.projectId;
    const region = this.region_;
    if (this.emulatorOrigin !== null) {
      const origin = this.emulatorOrigin;
      return `${origin}/${projectId}/${region}/${name}`;
    }
    return `https://${region}-${projectId}.cloudfunctions.net/${name}`;
  }

  private async call(name: string, data: any, defaultHeaders: any): Promise<HttpsCallableResult> {
    const url = this._url(name);

    // Encode any special types, such as dates, in the input data.
    data = this.serializer.encode(data);
    const body = { data };

    // Add a header for the authToken.
    const headers = new Headers(defaultHeaders);
    const context = await this.contextProvider.getContext();
    if (context.authToken) {
      headers.append('Authorization', 'Bearer '   context.authToken);
    }
    if (context.instanceIdToken) {
      headers.append('Firebase-Instance-ID-Token', context.instanceIdToken);
    }

    const response = await this.postJSON(url, body, headers);

    // Check for an error status, regardless of http status.
    const error = _errorForResponse(
      response.status,
      response.json,
      this.serializer
    );
    if (error) {
      throw error;
    }

    if (!response.json) {
      throw new HttpsErrorImpl(
        'internal',
        'Response is not valid JSON object.'
      );
    }

    let responseData = response.json.data;
    // TODO(klimt): For right now, allow "result" instead of "data", for
    // backwards compatibility.
    if (typeof responseData === 'undefined') {
      responseData = response.json.result;
    }
    if (typeof responseData === 'undefined') {
      // Consider the response malformed.
      throw new HttpsErrorImpl('internal', 'Response is missing data field.');
    }

    // Decode any special types, such as dates, in the returned data.
    const decodedData = this.serializer.decode(responseData);

    return { data: decodedData };
  }