With #113, the spec says:

If there are no share targets available:
   Reject [[sharePromise]] with an "AbortError" DOMException.

However, in the above, it's possible that there is no share service available at all (or the service may fail to be initiated). It's not really possible to know this beforehand if it will succeed. In such a case, it may be more suitable to reject with a "NotSupportedError".