func (r *Request) ResponseHeaders() string {
	return r.Call("getAllResponseHeaders").String()
}
ResponseHeaders returns all response headers.
package xhr  
import (
	"errors"
	"github.com/gopherjs/gopherjs/js"
	"honnef.co/go/js/util"
)
const (
	Unsent = iota
	Opened
	HeadersReceived
	Loading
	Done
)
const (
	ArrayBuffer = "arraybuffer"
	Blob        = "blob"
	Document    = "document"
	JSON        = "json"
	Text        = "text"
)
type Request struct {
	*js.Object
	util.EventTarget
	ReadyState      int        `js:"readyState"`
	Response        *js.Object `js:"response"`
	ResponseText    string     `js:"responseText"`
	ResponseType    string     `js:"responseType"`
	ResponseXML     *js.Object `js:"responseXML"`
	Status          int        `js:"status"`
	StatusText      string     `js:"statusText"`
	Timeout         int        `js:"timeout"`
	WithCredentials bool       `js:"withCredentials"`
	ch chan error
}
type Upload struct {
	*js.Object
	util.EventTarget
}
func (r *Request) Upload() *Upload {
	o := r.Get("upload")
	return &Upload{o, util.EventTarget{Object: o}}
}
var ErrAborted = errors.New("request aborted")
var ErrTimeout = errors.New("request timed out")
var ErrFailure = errors.New("send failed")
func NewRequest(method, url string) *Request {
	o := js.Global.Get("XMLHttpRequest").New()
	r := &Request{Object: o, EventTarget: util.EventTarget{Object: o}}
	r.Call("open", method, url, true)
	return r
}