How to get all headers in angular2

Question

I need to get an array of headers in an http get request, but I can only see part of them.

How can I get all the headers that I see in response?

Service for receiving http request

getUserRevenuePerPage(numberOfBils) {
return this._http.get(environment.apiUrl + environment.apiOldSubPath + this._expertRevenueUrl +
  '?perPage=' + numberOfBils);

}

Method for receiving an array of headers from a response

getUserRevenuePerPage() {
return this._revenueService.getUserRevenuePerPage(this.numberOfBills).subscribe((data) => {
  this.header = data.headers.toJSON()
});

}