HttpRequest from dart:html don't not work in web workers on Safari

[simolus3]

XMLHttpRequests which, according to MDN should work in regular web workers, don't work in Safari web workers when used through dart:html.

To reproduce this issue, setup a new Dart web project from the template (dart create -t xhr_worker). Create a new file web/worker.dart with the following content:

import 'dart:html';

void main() async {
  print(await HttpRequest.getString('index.html'));
}

Also, change web/main.dart as follows:

import 'dart:html';

void main() async {
  Worker('worker.dart.js');
}

I run this example with dart run build_runner serve "--define=build_web_compilers:entrypoint=compiler=dart2js" web:8080.

This works in Firefox and in Chrome, but fails in Safari (throws in _failedAsCheck, where object is an XMLHttpRequestProgressEvent and testRti is the RTI for Event).
Also, it's interesting that J.getInterceptor$(new Event('a')) returns a Dart Event, but J.getInterceptor$(object) returns an UnknownJavaScriptObject, even though the object is an event as well. I suspect this is because, despite these events being delivered in workers, the global scope for workers does not include XMLHttpRequestProgressEvent in Safari. Is there a way for the Dart SDK to work around this issue?

[tangenttechno]

same issue for me too. Runs fine in chrome. but fails in safari.