public EventRequestHeadersListener(PollingXHR pollingXHR) => this.pollingXHR = pollingXHR;
public EventResponseHeadersListener(PollingXHR pollingXHR) => _pollingXhr = pollingXHR;
public SendEventErrorListener(PollingXHR pollingXHR) => _pollingXhr = pollingXHR;