Detect if two dates are in the same week based on UTC time

areSameWeek.js

function areSameWeeksUTC(date1, date2, boundaryDay=0)
{
    if(date1 > date2)
    {
        let t = date1;
        date1 = date2;
        date2 = t;
    }
    
    if(((((date2 - date1)/1000)/3600)/24)>6)
    {
        return false;
    }

    let day1 = date1.getUTCDay();
    let day2 = date2.getUTCDay();
    
    if(day1 == boundaryDay)
    {
        return true;
    }

    if(day2 == boundaryDay)
    {
        return false;
    }

    let d1BoundaryDist = ((day1-boundaryDay)+7)%7;
    let d2BoundaryDist = ((day2-boundaryDay)+7)%7;

    if(d1BoundaryDist <= d2BoundaryDist)
    {
        return true;
    }
    
    return false;
}

boundaryDay allows you to set which day is the start of the week. It defaults to 0 (Sunday).
If date1 is later than date2 the dates get swapped around.