Microsoft Excel's Networkdays on Javascript

Here is a small snippet I made to do Networkdays function of MS Excel in Javascript.

networkdays = function(startDate,endDate){ 
 var startDate = typeof startDate=='object' ? startDate: new Date(startDate);
 var endDate = typeof endDate=='object' ? endDate: new Date(endDate);
 if (endDate > startDate){
  var days  = Math.ceil((endDate.setHours(23,59,59,999) - startDate.setHours(0,0,0,1)) / (86400 * 1000));
  var weeks  = Math.floor(Math.ceil((endDate.setHours(23,59,59,999) - startDate.setHours(0,0,0,1)) / (86400 * 1000)) / 7);

  days = days - (weeks * 2);
  days = startDate.getDay() - endDate.getDay() > 1 ? days - 2 : days;
  days = startDate.getDay() == 0 && endDate.getDay() != 6 ? days - 1 : days;
  days = endDate.getDay() == 6 && startDate.getDay() != 0 ? days - 1 : days;    

  return days;
 }
 return null;
};

Usage: networkdays('08/05/2016','08/30/2016'); OR networkdays(new Date(), '08/30/2016'); Accepts both strings and date object on both or any of the parameters. Enjoy!