Calculate an expected delivery date (accounting for holidays) in business days using JavaScript?

Question

After revisiting this script, and some modifications, the following is available to allow a user to add a feature that calculates the expected delivery date.

// array of ISO YYYY-MM-DD format dates
publicHolidays = {
    uk:["2020-01-01","2020-04-10","2020-04-13","2020-05-08","2020-05-25",
        "2020-08-03","2020-08-31","2020-12-25","2020-12-28"],
    usa:["2020-01-01","2020-01-20","2020-02-14","2020-02-17","2020-04-10",
        "2020-04-12","2020-05-10","2020-05-25","2020-06-21","2020-07-03",
        "2020-07-04","2020-09-07","2020-10-12","2020-10-31","2020,11,11",
        "2020-11-26","2020-12-25"]
}
// check if there is a match in the array
Date.prototype.isPublicHoliday = function( data ){// we check for a public holiday
    if(!data) return 1;
return data.indexOf(this.toISOString().slice(0,10))>-1? 0:1;
}

// calculation of business days
Date.prototype.businessDays = function( d, holidays ){
    var holidays = holidays || false, t = new Date( this ); // copy date.
    while( d ){ // we loop while d is not zero...   
        t.setDate( t.getDate() + 1 ); // set a date and test it
        switch( t.getDay() ){ // switch is used to allow easier addition of other days of the week
            case 0: case 6: break;// sunday & saturday
            default: // check if we are a public holiday or not
                d -= t.isPublicHoliday( holidays ); 
        }
    }
    return t.toISOString().slice(0,10); // just the YYY-MM-DD 
}

// dummy var, could be a form field input
OrderDate = "2020-02-12";
// test with a UK holiday date
var deliveryDate = new Date(OrderDate).businessDays(7, publicHolidays.usa);
// expected output 2020-02-25
console.log("Order date: %s, Delivery date: %s",OrderDate,deliveryDate );

Order date: 2020-02-12, Delivery date: 2020-02-25

---

The prototype is written to allow inputs from forms (HTML5 forms) of date type inputs as they are already in an ISO YYYY-MM-DD format and the output is formatted as such should that be needing to update a particular field.

The typical use would be...

var delDate = new Date( ISOdate ).businessDays( addBusinessDays, holidayData );

where the delDate is an ISO format date, eg, 2020-01-01

Answer 1

I've adapted Mark Giblin's revised code to better deal with end of year dates and also U.S. federal holidays. See below...

function businessDaysFromDate(date,businessDays) {
  var counter = 0, tmp = new Date(date);
  while( businessDays>=0 ) {
    tmp.setTime( date.getTime() + counter * 86400000 );
    if(isBusinessDay (tmp)) {
      --businessDays;
    }
    ++counter;
  }
  return tmp;
}

function isBusinessDay (date) {
  var dayOfWeek = date.getDay();
  if(dayOfWeek === 0 || dayOfWeek === 6) {
    // Weekend
    return false;
  }

  holidays = [
    '12/31+5', // New Year's Day on a saturday celebrated on previous friday
    '1/1',     // New Year's Day
    '1/2+1',   // New Year's Day on a sunday celebrated on next monday
    '1-3/1',   // Birthday of Martin Luther King, third Monday in January
    '2-3/1',   // Washington's Birthday, third Monday in February
    '5~1/1',   // Memorial Day, last Monday in May
    '7/3+5',   // Independence Day
    '7/4',     // Independence Day
    '7/5+1',   // Independence Day
    '9-1/1',   // Labor Day, first Monday in September
    '10-2/1',  // Columbus Day, second Monday in October
    '11/10+5', // Veterans Day
    '11/11',   // Veterans Day
    '11/12+1', // Veterans Day
    '11-4/4',  // Thanksgiving Day, fourth Thursday in November
    '12/24+5', // Christmas Day
    '12/25',   // Christmas Day
    '12/26+1',  // Christmas Day
  ];

  var dayOfMonth = date.getDate(),
  month = date.getMonth() + 1,
  monthDay = month + '/' + dayOfMonth;

  if(holidays.indexOf(monthDay)>-1){
    return false;
  }

  var monthDayDay = monthDay + '+' + dayOfWeek;
  if(holidays.indexOf(monthDayDay)>-1){
    return false;
  }

  var weekOfMonth = Math.floor((dayOfMonth - 1) / 7) + 1,
      monthWeekDay = month + '-' + weekOfMonth + '/' + dayOfWeek;
  if(holidays.indexOf(monthWeekDay)>-1){
    return false;
  }

  var lastDayOfMonth = new Date(date);
  lastDayOfMonth.setMonth(lastDayOfMonth.getMonth() + 1);
  lastDayOfMonth.setDate(0);
  var negWeekOfMonth = Math.floor((lastDayOfMonth.getDate() - dayOfMonth - 1) / 7) + 1,
      monthNegWeekDay = month + '~' + negWeekOfMonth + '/' + dayOfWeek;
  if(holidays.indexOf(monthNegWeekDay)>-1){
    return false;
  }

  return true;
}