In other words : 1 - "watch" needs a webhook HTTPS server for listening to the Gcal pushes 2 - "watch" can use the sustained POST connection to receive the pushed responses 3 - "watch" doesn't work and we have to make GET polling with : GET https://www.googleapis.com/calendar/v3/calendars/calendarId/events/eventId
In other words : how to get notification of events change using a single browser ?