Function
The duration in seconds. Fractions are truncated.
Optionalseparator: string = ":"
What to place between the parts.
The formatted duration.
Format a duration in seconds as "MM:SS", both parts zero-padded. Minutes are not capped at
60, so a long duration reads as "90:00" rather than rolling into hours — use formatHHMMSS for that.
formatMMSS