Provide a means to check if the API is supported by the platform or OS

[marcoscaceres]

The current spec presumes that if the OS or user agent doesn't support a sharing capability or intent, then the API shouldn't be exposed (i.e., navigator.share() would be undefined)... the problem is that this can then be misused with other features to potentially detect a user agent type or platform.

What we should actually have is a dedicated way to check if sharing is supported. The OS/browser/user should be allowed to lie should it choose to for whatever reason (e.g., the user is allergic to share sheets).

[saschanaz]

The OS/browser/user should be allowed to lie should it choose to for whatever reason (e.g., the user is allergic to share sheets).

This seems to be the real intent than the platform support indication as described by the title, is that correct? (Otherwise I'm not sure why the current behavior is insufficient, as there are easier ways to detect platforms, namely navigator.userAgent.)

Assuming that, I'm not sure such user intent should be exposed too easily, because that would be a good fingerprinting vector.

[marcoscaceres]

Yes, exactly. It should guard against exposing any user preference (or be obscure enough that it can't be used to fingerprint).

You are correct that navigator.userAgent provides some this, but, for instance, it's shouldn't be possible to detect if you are on an iPhone or an iPad via navigator.userAgent.