Should getDisplayMedia be undefined on platforms with no support?

[jan-ivar]

A question came up on stackoverflow: How to detect if screen sharing is supported on a particular browser and platform? Presumably this is to avoid showing users a non-functioning button.

It turns out mobile browsers like Chrome for Android and Firefox for Android define the API surface, but don't actually implement it, instead always rejecting with NotAllowedError.

This defeats feature-detection. Should those browsers instead have left navigator.mediaDevices.getDisplayMedia undefined?

Unlike with camera or microphone (which is detectable today, modulo discussions in w3c/mediacapture-main#612 about maybe lying about this for privacy reasons), this would appear to leak no net fingerprinting surface about a user's system, since sites can already browser-sniff this from the UA string.

[youennf]

It seems like a Chromium bug (is there a bug filed there?).
I am not sure the spec should say anything here.

[aboba]

@jan-ivar Agree with Youenn that this is a bug. Support for feature detection is recommended in the Client-side API Design Principles. In this case, I see no reason to circumvent that recommendation.

[LukasKalbertodt]

There is a bug report for Chromium. I also just created a bug report for Firefox.

[jan-ivar]

Bugs have been filed on implementations so we can close this.