I wonder if we can simplify canShare() a bit... right now, canShare() conflates type checking behavior by intertwining the method call with share(). This is problematic because share() returns a promise, not TypeErrors.

Over on Mozilla’s bugzilla, @ericwilligers mentioned that the intent of canShare() is to avoid having to do UA sniffing. As such, why don’t we this instead:

enum Shareable {
  "file”,
  "url”,
   // and so on...
}

partial interface Navigator {
   boolean canShare(sequence<Shareable> members);
}

That greatly simplifies things by deferring the support checking to the IDL layer. That causes the IDL layer to throw if passed some unsupported Shareable type. The result being that it either returns true or throws.

If throwing is not palatable, then an alternative would be to take a sequence of DOMStrings, then return false if the names don’t match a supported member type.