Optional callback that returns a fresh URL on each reconnection attempt.
When provided, the EventSource implementation should call this instead of
reusing the original URL. This allows query parameters (e.g. basis) to
be updated between reconnections.
Optional callback that returns a fresh URL on each reconnection attempt. When provided, the EventSource implementation should call this instead of reusing the original URL. This allows query parameters (e.g.
basis) to be updated between reconnections.