The statusText property of Response is unclear for HTTP/2.

HTTP/2 does not include a status message / reason like HTTP/1.1: RFC 7540

8.1.2.4. Response Pseudo-Header Fields
...
HTTP/2 does not define a way to carry the version or reason phrase
that is included in an HTTP/1.1 status line.

The Fetch spec simply defines statusText as the status message value, which unless otherwise specified is OK.

For HTTP/2 it seems status message could be interpreted any number of ways:

• empty string - because there is no reason phrase
• "OK" - because that is always the default (would be weird to have a 404 OK though)
• implementation defined - such as some default reason text for a status code

Different browser behaviors. Test on an HTTP/2 capable domain.

fetch("/").then((r) => console.log(r.statusText)); // 200

• Chrome: ""
• Firefox: "OK"
• Safari: "HTTP/2.0 200"

fetch("/doesnotexistasdf").then((r) => console.log(r.statusText)); // 404

• Chrome: ""
• Firefox: "Not Found"
• Safari: "HTTP/2.0 404"