OptionalbodyOptionalinitialOptionalmethodOptionalretryA custom strategy that replaces the built-in (default) one. When provided,
the EventSource defers all reconnection timing to it and the built-in
options (initialRetryDelayMillis, retryResetIntervalMillis) are ignored.
OptionalretryOptionalurlOptional 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.
The initial delay and reset window for the built-in (default) retry-delay strategy. These configure the default behavior; they are ignored when a custom retryDelayStrategy is provided, since that strategy then owns all reconnection timing.