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JavaScript

function dateDifference(start, end) {

  // Copy date objects so don't modify originals
  
  var s = new Date(start);
  var e = new Date(end);
  
	var addOneMoreDay = 0;
	if( s.getDay() == 0 || s.getDay() == 6 ) {
  	addOneMoreDay = 1;
  }
  
  // Set time to midday to avoid dalight saving and browser quirks
  s.setHours(12,0,0,0);
  e.setHours(12,0,0,0);

  // Get the difference in whole days
  var totalDays = Math.round((e - s) / 8.64e7);

  // Get the difference in whole weeks
  var wholeWeeks = totalDays / 7 | 0;

  // Estimate business days as number of whole weeks * 5
  var days = wholeWeeks * 5;

  // If not even number of weeks, calc remaining weekend days
  if (totalDays % 7) {
    s.setDate(s.getDate() + wholeWeeks * 7);

    while (s < e) {
      s.setDate(s.getDate() + 1);

      // If day isn't a Sunday or Saturday, add to business days
      if (s.getDay() != 0 && s.getDay() != 6) {
        ++days;
      }
      //s.setDate(s.getDate() + 1);
    }
  }
  var weekEndDays = totalDays - days + addOneMoreDay;
  return weekEndDays;
}

var date1 = "2017-03-11";
var date2 = "2017-03-20";
alert(dateDifference( date1, date2));