Function getFirstTimestampOfUnit

src/scale/Time.ts:447–450

(timestamp: number, unitName: TimeUnit, isUTC: boolean)

// e.g., if the input unit is 'day', start calculate ticks from the first day of
// that month to make ticks "nice".
function getFirstTimestampOfUnit(timestamp: number, unitName: TimeUnit, isUTC: boolean) {
    const upperUnitIdx = Math.max(0, indexOf(primaryTimeUnits, unitName) - 1);
    return roundTime(new Date(timestamp), primaryTimeUnits[upperUnitIdx], isUTC).getTime();
}

function createEstimateNiceMultiple(
    setMethodName: JSDateSetterNames,