moment.isocalendar.js

if ( typeof require !== 'undefined' )
{
  moment = require('moment');
}

;(function(moment) {

  var firstIsoWeekOfYear = function(year) {
        var m = moment([year])
          , day = m.day();

        if ( day === 0 )
        {
          day = 7;
        }

        // ISO week is the first week with a Thursday, so if the first
        // day of the year is Friday, move to next Sunday.
        if ( day > 4 ) {
          m.add('weeks', 1);
        }

        m.subtract('days', day - 1);

        return m;
      }

      // 0 => year, 1 => week, 2 => day, 3 => minute
    , index_method_map = ['year', 'week', 'day', 'minute']

      // This method powers the getter/setter methods
    , genericAccessor = function(index, value) {
        if ( value )
        {
          var iso = this.isocalendar();
          iso[index] = value;
          this._d = moment.fromIsocalendar(iso).toDate();
          return this;
        }
        else
        {
          return this.isocalendar()[index];
        }
      }

      // Helper method for tying together the getter/setters.
    , accessorFactory = function(index) {
        return function(value) {
          return genericAccessor.call(this, index, value);
        };
      }
    ;

  moment.fn.isocalendar = function() {
    var year = this.year()
      , firstMonday = firstIsoWeekOfYear(year)
      , week = Math.floor(this.diff(firstMonday, 'weeks', true)) + 1
      , day = this.day()
      , minute = this.hours() * 60 + this.minutes()
      ;

    if ( week == 53 && firstIsoWeekOfYear(year + 1) <= this )
    {
      year += 1;
      week = 1;
    }
    else if ( week < 1 )
    {
      year -= 1;
      week = moment([year, 11, 31, 0, 0]).isocalendar()[1];
    }

    if ( day === 0 )
    {
      day = 7;
    }

    return [ year
           , week
           , day
           , minute
           ];
  };

  moment.fromIsocalendar = function(array) {
    var date = firstIsoWeekOfYear(array[0]).add({
      weeks: array[1] - 1
    , days: array[2] - 1
    , minutes: array[3]
    });

    return date;
  };

  // isoyear, isomonth, isoday, isominute setters.
  for (var i = 0, _len = index_method_map.length; i < _len; i++) {
    moment.fn['iso' + index_method_map[i]] = accessorFactory(i);
  }

})(moment);