wrtc.getScreen() starts screensharing, the contents of your screen is transmitted as video media stream to the caller. She will no longer see your camera image but your screen's contents. She will however still be able to hear you.
To stop screensharing call wrtc.getScreen(false)
wrtc.getScreen(enable, constraints)
call wrtc.getScreen() or wrtc.getScreen(true)
call wrtc.getScreen(false)
The user can also end screensharing manually using the ESC button.
Nothing.
If screensharing is not supported by web browser calling wrtc.getScreen() will result in wrtc.onError(703, "browser reports getScreen not available")