This is an archived snapshot of W3C's public bugzilla bug tracker, decommissioned in April 2019. Please see the home page for more details.
.
It's [NoInterfaceObject]...
Yes, but Exposed on an interface affects not just its visibility in global scope but also the visibility of its members. And the default visibility is "Window only". So the way the spec is written right now, the members of XMLHttpRequestEventTarget are only exposed in window scopes. Either those members need [Exposed] or the interface itself does.
https://github.com/whatwg/xhr/commit/59512a70107244a3810662a8d8feb1f9fa2d9042