When I use an Android device, how can I know whether the current page is running in a browser or in captive portal, only by Javascript methods

Question

in iOS, if page is running in captive, "safari" will not in appear userAgent.

But in android devices, how can I judge it? localStorage and FetchApi are supported in some android system , we can no longer judge by them.

Judging from "Verison" fields of userAgent is perhaps inaccurate