code: function makeHoliday(date, info, observedInfo) {
  
    // always make the holiday.
    var holiday = {
      info: info,
      date: {
        month: date.getMonth(),
        day  : date.getDate()
      }
    }
  
    // if the holiday info's `bank` value has a function then
    // give it the date so it can evaluate the value.
    if ('function' === typeof info.bank) {
      info.bank = info.bank(date)
    }
  
    // without an observed holiday we return only the main holiday
    if (date.observed == null) {
      return holiday
    }
  
    // there's an observed date so return both holidays in an array.
    else {
      return [
        holiday, // main holiday
        {        // observed holiday
          info: observedInfo,
          date: {
            month: date.observed.getMonth(),
            day  : date.observed.getDate()
          }
        }
      ]
    }
  }
docs: helper function which accepts the calculated holiday date and holiday info's. if an observed date was produced then it returns both holidays. also helps with the `bank` boolean value.