Function pause_before 

pub fn pause_before(attempt: u32, first: Duration) -> Duration

What: The pause before try number attempt (the first new try is number one): the first pause, doubled each time, never past the longest. Why: Short pauses mend a stall quickly; longer ones keep a host that is offline for an hour from being asked every few seconds.

In TS you’d write (pseudocode):

Math.min(first * 2 ** (attempt - 1), LONGEST)