format
Formats this Duration as d:HH:MM:SS (or d:HH:MM:SS.mmm when includeMillis is true).
Negative durations are prefixed with -; one that rounds down to zero milliseconds has no sign. An infinite duration formats as the largest finite one, 106751991167:07:12:55, with a - when negative.
Extension function on Duration.
Return
the formatted duration string
Parameters
includeMillis
whether to include milliseconds in the output (default false)