code: function jWeekOfYear(mom, firstDayOfWeek, firstDayOfWeekOfYear) {
      var end = firstDayOfWeekOfYear - firstDayOfWeek
          , daysToDayOfWeek = firstDayOfWeekOfYear - mom.day()
          , adjustedMoment;
  
      if (daysToDayOfWeek > end) {
          daysToDayOfWeek -= 7;
      }
      if (daysToDayOfWeek < end - 7) {
          daysToDayOfWeek += 7;
      }
      adjustedMoment = jMoment(mom).add(daysToDayOfWeek, "d");
      return  { week: Math.ceil(adjustedMoment.jDayOfYear() / 7)
          , year: adjustedMoment.jYear()
      };
  }
docs: **********************************
  Week of Year
  **********************************