JavaScript function to get Working days between 2 days without weekends(Saturday,Sunday) and some custom holidays

get-working-days.js

var getWorkingDays = function(start,endCount,holidays){		
		var weekdays = [];
		var current = start;

		var i = 0; 
		while(i < endCount){
			if (!isWeekEnd(current)) {
				weekdays.push(current);
				i++;
			}
			currentObj = new Date(current);
			current = currentObj.addDays(1).format();
		}

		function isWeekEnd(date){
			dateObj = new Date(date);
			if (dateObj.getDay() == 6 || dateObj.getDay() == 0) {
				return true;
			}else{
				if (holidays.contains(date)) {
					return true;
				}else{
					return false;
				}
			}
		}

		return weekdays;
	}

	// check if weekend
	isWeekEnd = function(date){
		date.getDay();
		return (dayOfWeek == 6 || dayOfWeek == 0);
	}

	// check if value exist in array
	Array.prototype.contains = function(obj) {
		var i = this.length;
		while (i--) {
			if (this[i] == obj) {
				return true;
			}
		}
		return false;
	}

	// get next day
	Date.prototype.addDays = function(days) {
		var dat = new Date(this.valueOf())
		dat.setDate(dat.getDate() + days);
		return dat;
	}

	//format date
	Date.prototype.format = function() {
		var mm = this.getMonth() + 1;
		var dd = this.getDate();
		if (mm < 10) {
			mm = '0' + mm;
		}
		if (dd < 10) {
			dd = '0' + dd;
		}
		return this.getFullYear()+'-'+mm+'-'+dd;
	};


	var start = '2016-10-01';
  var daysAhead = 20;
	var holidayList = ['2016-10-15','2016-10-20','2016-10-19','2016-10-18'];

	var result = getWorkingDays(start,daysAhead,holidayList);
  result.forEach(function(item,index){
  	document.getElementById('result').insertAdjacentHTML('beforeend','<span>'+item+'<br>');
  })
	console.log(result);