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WeekOfDay Count Calculator created by davidsk - https://repl.it/DFqJ/25
var DayOfWeek = {
Sunday: 0,
Monday: 1,
Tuesday: 2,
Wednesday: 3,
Thursday: 4,
Friday: 5,
Saturday: 6
};
function CountWeekdayInPeriod(targetDayIndex, startDayIndex, periodDuration){
// ensure values are integers; js will concatenate string values
startDayIndex = parseInt(startDayIndex, 10),
periodDuration = parseInt(periodDuration, 10);
// find the number of days in addition to whole weeks
var partialWeekLagDayCount = periodDuration % 7;
// whichever day is being targeted, there is always one instance every 7 days
var dayCount = (periodDuration - partialWeekLagDayCount) / 7;
// determine the start day index having 'rotated' the days so that the target day is now index 7
var firstDayIndex = ((startDayIndex + (6 - targetDayIndex)) % 7 ) + 1
// calculate the end date's day index by adding the period to the adjusted start date index
// 1 is deducted as the start date already considered
var firstDayPlusDurationIndex = firstDayIndex + partialWeekLagDayCount - 1;
// determine the weekday index of the last day of the remaining period
var lastWeekdayIndex = (firstDayPlusDurationIndex % 7);
// determine whether the remaining period has 'gone around the horn'
var secondIteration = (firstDayPlusDurationIndex - lastWeekdayIndex) / 7;
dayCount += secondIteration;
return dayCount;
}
// functions built on top of CountWeekdayInPeriod
function CountWeekendDaysInPeriod(startDayIndex, periodDuration)
{
return CountWeekdayInPeriod(DayOfWeek.Saturday, startDayIndex, periodDuration) + CountWeekdayInPeriod(DayOfWeek.Sunday, startDayIndex, periodDuration);
}
function GetNextWeekday(startDate, periodDuration){
var weekendDayCount, totalWeekendDays = 0, iterativePeriodDuration = periodDuration;
if(!iterativePeriodDuration || iterativePeriodDuration === 0){
iterativePeriodDuration = 1;
}
var direction = iterativePeriodDuration / Math.abs(iterativePeriodDuration);
var internalStartDate = new Date(startDate);
if(direction === -1){
internalStartDate.setDate(internalStartDate.getDate() + iterativePeriodDuration);
}
var startDayIndex = internalStartDate.getDay();
do{
weekendDayCount = CountWeekendDaysInPeriod(startDayIndex, Math.abs(iterativePeriodDuration));
iterativePeriodDuration = weekendDayCount;
startDayIndex = (7 + startDayIndex + (direction * (iterativePeriodDuration % 7))) % 7;
totalWeekendDays += weekendDayCount;
} while(weekendDayCount > 0);
var totalDelta = periodDuration + (direction * totalWeekendDays);
return new Date(new Date(startDate).setDate(startDate.getDate() + totalDelta));
}
// usage
var weekdaysInPeriod = CountWeekdayInPeriod(DayOfWeek.Wednesday, DayOfWeek.Tuesday, 10);
console.log("weekdaysInPeriod: " + weekdaysInPeriod);
var weekendDaysInPeriod = CountWeekendDaysInPeriod(DayOfWeek.Tuesday, 11);
console.log("weekendDaysInPeriod: " + weekendDaysInPeriod);
var nextWorkingDay = GetNextWeekday(new Date(2016, 8, 24), 0);
console.log("nextWorkingDay: " + nextWorkingDay);
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