function getBusinessDateCount (startDate, endDate) {
    var elapsed, daysBeforeFirstSaturday, daysAfterLastSunday;
    var ifThen = function (a, b, c) {
        return a == b ? c : a;
    };
 
    elapsed = endDate - startDate;
    elapsed /= 86400000;
 
    daysBeforeFirstSunday = (7 - startDate.getDay()) % 7;
    daysAfterLastSunday = endDate.getDay();
 
    elapsed -= (daysBeforeFirstSunday + daysAfterLastSunday);
    elapsed = (elapsed / 7) * 5;
    elapsed += ifThen(daysBeforeFirstSunday - 1, -1, 0) + ifThen(daysAfterLastSunday, 6, 5);
 
    return Math.ceil(elapsed);
 
    /* 2015-04-29 til 2015-04-29 will return 1
    if you want it to return 0 instead 1:
    change Math.ceil() to parseInt() in last line */
}
 
 
var date1 = new Date(1999, 12, 31);
var date2 = new Date(); // now
 
print( getBusinessDateCount(date1, date2) );
 
 

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