weekdays-between.js

function datePart(datetime) {
				return new Date(datetime.getFullYear(), datetime.getMonth(), datetime.getDate());
			}

			function daysFromNextWeekday(weekday, weekdayRef) {
				return ((weekdayRef - weekday) + 7) % 7;
			}

			function amountOfWeekdayInRange(startWeekday, weekdayRef, dayCount) {
				const daysToFirstOccurence = daysFromNextWeekday(startWeekday, weekdayRef);
				if (daysToFirstOccurence <= dayCount) {
					const daysFromFirstOccurence = dayCount - daysToFirstOccurence;
					return 1 + Math.floor(daysFromFirstOccurence / 7);
				} else {
					return 0;
				}
			}

			function weekDaysBetween(datetime1, datetime2) {
				if (!datetime1 || !datetime2) {
					return 0;
				}
				const date1 = datePart(datetime1);
				const date2 = datePart(datetime2);
				const daysBetween = Math.round((date2.getTime() - date1.getTime()) / (1000 * 3600 * 24));
				// convert to monday = 0 (from sunday = 0)
				const startWeekday = (date1.getDay() + 7 - 1) % 7;


				let amountOfSaturdays = amountOfWeekdayInRange(startWeekday, 5, daysBetween);
				let amountOfSundays = amountOfWeekdayInRange(startWeekday, 6, daysBetween);
				return daysBetween - amountOfSaturdays - amountOfSundays;
			}