helper.js

var timezones = function() {
  zones =  [
  
    { value: "Abu Dhabi", label: "Abu Dhabi" },
  
    { value: "Adelaide", label: "Adelaide" },
  
    { value: "Alaska", label: "Alaska" },
  
    { value: "Almaty", label: "Almaty" },
  
    { value: "America/Los_Angeles", label: "America/Los_Angeles" },
  
    { value: "American Samoa", label: "American Samoa" },
  
    { value: "Amsterdam", label: "Amsterdam" },
  
    { value: "Arizona", label: "Arizona" },
  
    { value: "Astana", label: "Astana" },
  
    { value: "Athens", label: "Athens" },
  
    { value: "Atlantic Time (Canada)", label: "Atlantic Time (Canada)" },
  
    { value: "Auckland", label: "Auckland" },
  
    { value: "Azores", label: "Azores" },
  
    { value: "Baghdad", label: "Baghdad" },
  
    { value: "Baku", label: "Baku" },
  
    { value: "Bangkok", label: "Bangkok" },
  
    { value: "Beijing", label: "Beijing" },
  
    { value: "Belgrade", label: "Belgrade" },
  
    { value: "Berlin", label: "Berlin" },
  
    { value: "Bern", label: "Bern" },
  
    { value: "Bogota", label: "Bogota" },
  
    { value: "Brasilia", label: "Brasilia" },
  
    { value: "Bratislava", label: "Bratislava" },
  
    { value: "Brisbane", label: "Brisbane" },
  
    { value: "Brussels", label: "Brussels" },
  
    { value: "Bucharest", label: "Bucharest" },
  
    { value: "Budapest", label: "Budapest" },
  
    { value: "Buenos Aires", label: "Buenos Aires" },
  
    { value: "Cairo", label: "Cairo" },
  
    { value: "Canberra", label: "Canberra" },
  
    { value: "Cape Verde Is.", label: "Cape Verde Is." },
  
    { value: "Caracas", label: "Caracas" },
  
    { value: "Casablanca", label: "Casablanca" },
  
    { value: "Central America", label: "Central America" },
  
    { value: "Central Time (US & Canada)", label: "Central Time (US & Canada)" },
  
    { value: "Chennai", label: "Chennai" },
  
    { value: "Chihuahua", label: "Chihuahua" },
  
    { value: "Chongqing", label: "Chongqing" },
  
    { value: "Copenhagen", label: "Copenhagen" },
  
    { value: "Darwin", label: "Darwin" },
  
    { value: "Dhaka", label: "Dhaka" },
  
    { value: "Dublin", label: "Dublin" },
  
    { value: "Eastern Time (US & Canada)", label: "Eastern Time (US & Canada)" },
  
    { value: "Edinburgh", label: "Edinburgh" },
  
    { value: "Ekaterinburg", label: "Ekaterinburg" },
  
    { value: "Fiji", label: "Fiji" },
  
    { value: "Georgetown", label: "Georgetown" },
  
    { value: "Greenland", label: "Greenland" },
  
    { value: "Guadalajara", label: "Guadalajara" },
  
    { value: "Guam", label: "Guam" },
  
    { value: "Hanoi", label: "Hanoi" },
  
    { value: "Harare", label: "Harare" },
  
    { value: "Hawaii", label: "Hawaii" },
  
    { value: "Helsinki", label: "Helsinki" },
  
    { value: "Hobart", label: "Hobart" },
  
    { value: "Hong Kong", label: "Hong Kong" },
  
    { value: "Indiana (East)", label: "Indiana (East)" },
  
    { value: "International Date Line West", label: "International Date Line West" },
  
    { value: "Irkutsk", label: "Irkutsk" },
  
    { value: "Islamabad", label: "Islamabad" },
  
    { value: "Istanbul", label: "Istanbul" },
  
    { value: "Jakarta", label: "Jakarta" },
  
    { value: "Jerusalem", label: "Jerusalem" },
  
    { value: "Kabul", label: "Kabul" },
  
    { value: "Kamchatka", label: "Kamchatka" },
  
    { value: "Karachi", label: "Karachi" },
  
    { value: "Kathmandu", label: "Kathmandu" },
  
    { value: "Kolkata", label: "Kolkata" },
  
    { value: "Krasnoyarsk", label: "Krasnoyarsk" },
  
    { value: "Kuala Lumpur", label: "Kuala Lumpur" },
  
    { value: "Kuwait", label: "Kuwait" },
  
    { value: "Kyiv", label: "Kyiv" },
  
    { value: "La Paz", label: "La Paz" },
  
    { value: "Lima", label: "Lima" },
  
    { value: "Lisbon", label: "Lisbon" },
  
    { value: "Ljubljana", label: "Ljubljana" },
  
    { value: "London", label: "London" },
  
    { value: "Madrid", label: "Madrid" },
  
    { value: "Magadan", label: "Magadan" },
  
    { value: "Marshall Is.", label: "Marshall Is." },
  
    { value: "Mazatlan", label: "Mazatlan" },
  
    { value: "Melbourne", label: "Melbourne" },
  
    { value: "Mexico City", label: "Mexico City" },
  
    { value: "Mid-Atlantic", label: "Mid-Atlantic" },
  
    { value: "Midway Island", label: "Midway Island" },
  
    { value: "Minsk", label: "Minsk" },
  
    { value: "Monrovia", label: "Monrovia" },
  
    { value: "Monterrey", label: "Monterrey" },
  
    { value: "Moscow", label: "Moscow" },
  
    { value: "Mountain Time (US & Canada)", label: "Mountain Time (US & Canada)" },
  
    { value: "Mumbai", label: "Mumbai" },
  
    { value: "Muscat", label: "Muscat" },
  
    { value: "Nairobi", label: "Nairobi" },
  
    { value: "New Caledonia", label: "New Caledonia" },
  
    { value: "New Delhi", label: "New Delhi" },
  
    { value: "Newfoundland", label: "Newfoundland" },
  
    { value: "Novosibirsk", label: "Novosibirsk" },
  
    { value: "Nuku'alofa", label: "Nuku'alofa" },
  
    { value: "Osaka", label: "Osaka" },
  
    { value: "Pacific Time (US & Canada)", label: "Pacific Time (US & Canada)" },
  
    { value: "Paris", label: "Paris" },
  
    { value: "Perth", label: "Perth" },
  
    { value: "Port Moresby", label: "Port Moresby" },
  
    { value: "Prague", label: "Prague" },
  
    { value: "Pretoria", label: "Pretoria" },
  
    { value: "Quito", label: "Quito" },
  
    { value: "Rangoon", label: "Rangoon" },
  
    { value: "Riga", label: "Riga" },
  
    { value: "Riyadh", label: "Riyadh" },
  
    { value: "Rome", label: "Rome" },
  
    { value: "Samoa", label: "Samoa" },
  
    { value: "Santiago", label: "Santiago" },
  
    { value: "Sapporo", label: "Sapporo" },
  
    { value: "Sarajevo", label: "Sarajevo" },
  
    { value: "Saskatchewan", label: "Saskatchewan" },
  
    { value: "Seoul", label: "Seoul" },
  
    { value: "Singapore", label: "Singapore" },
  
    { value: "Skopje", label: "Skopje" },
  
    { value: "Sofia", label: "Sofia" },
  
    { value: "Solomon Is.", label: "Solomon Is." },
  
    { value: "Sri Jayawardenepura", label: "Sri Jayawardenepura" },
  
    { value: "St. Petersburg", label: "St. Petersburg" },
  
    { value: "Stockholm", label: "Stockholm" },
  
    { value: "Sydney", label: "Sydney" },
  
    { value: "Taipei", label: "Taipei" },
  
    { value: "Tallinn", label: "Tallinn" },
  
    { value: "Tashkent", label: "Tashkent" },
  
    { value: "Tbilisi", label: "Tbilisi" },
  
    { value: "Tehran", label: "Tehran" },
  
    { value: "Tijuana", label: "Tijuana" },
  
    { value: "Tokelau Is.", label: "Tokelau Is." },
  
    { value: "Tokyo", label: "Tokyo" },
  
    { value: "UTC", label: "UTC" },
  
    { value: "Ulaan Bataar", label: "Ulaan Bataar" },
  
    { value: "Urumqi", label: "Urumqi" },
  
    { value: "Vienna", label: "Vienna" },
  
    { value: "Vilnius", label: "Vilnius" },
  
    { value: "Vladivostok", label: "Vladivostok" },
  
    { value: "Volgograd", label: "Volgograd" },
  
    { value: "Warsaw", label: "Warsaw" },
  
    { value: "Wellington", label: "Wellington" },
  
    { value: "West Central Africa", label: "West Central Africa" },
  
    { value: "Yakutsk", label: "Yakutsk" },
  
    { value: "Yerevan", label: "Yerevan" },
  
    { value: "Zagreb", label: "Zagreb" }
  
  ];
  
  return zones;
};

var currentTimeZone = function() {
  var date = new Date();
  var offset = (date.getTimezoneOffset() / 60);
  numbers = offset.toString().split('.')
  hh = parseInt(numbers[0], 10);
  hh = Math.abs(hh) * (hh < 0 ? 1 : -1).toString();
  mm = numbers.length > 1 ? (parseInt(numbers[1], 10) * 6 / 10).toString() : '00';
  zone = { value: [hh, mm].join(''), label: getTimezoneName()};
  return zone;
};

var getTimezoneName = function() {
  tmSummer = new Date(Date.UTC(2005, 6, 30, 0, 0, 0, 0));
	so = -1 * tmSummer.getTimezoneOffset();
	tmWinter = new Date(Date.UTC(2005, 12, 30, 0, 0, 0, 0));
	wo = -1 * tmWinter.getTimezoneOffset();

	if (-660 == so && -660 == wo) return 'Pacific/Midway';
	if (-600 == so && -600 == wo) return 'Pacific/Tahiti';
	if (-570 == so && -570 == wo) return 'Pacific/Marquesas';
	if (-540 == so && -600 == wo) return 'America/Adak';
	if (-540 == so && -540 == wo) return 'Pacific/Gambier';
	if (-480 == so && -540 == wo) return 'US/Alaska';
	if (-480 == so && -480 == wo) return 'Pacific/Pitcairn';
	if (-420 == so && -480 == wo) return 'US/Pacific';
	if (-420 == so && -420 == wo) return 'US/Arizona';
	if (-360 == so && -420 == wo) return 'US/Mountain';
	if (-360 == so && -360 == wo) return 'America/Guatemala';
	if (-360 == so && -300 == wo) return 'Pacific/Easter';
	if (-300 == so && -360 == wo) return 'US/Central';
	if (-300 == so && -300 == wo) return 'America/Bogota';
	if (-240 == so && -300 == wo) return 'US/Eastern';
	if (-240 == so && -240 == wo) return 'America/Caracas';
	if (-240 == so && -180 == wo) return 'America/Santiago';
	if (-180 == so && -240 == wo) return 'Canada/Atlantic';
	if (-180 == so && -180 == wo) return 'America/Montevideo';
	if (-180 == so && -120 == wo) return 'America/Sao_Paulo';
	if (-150 == so && -210 == wo) return 'America/St_Johns';
	if (-120 == so && -180 == wo) return 'America/Godthab';
	if (-120 == so && -120 == wo) return 'America/Noronha';
	if (-60 == so && -60 == wo) return 'Atlantic/Cape_Verde';
	if (0 == so && -60 == wo) return 'Atlantic/Azores';
	if (0 == so && 0 == wo) return 'Africa/Casablanca';
	if (60 == so && 0 == wo) return 'Europe/London';
	if (60 == so && 60 == wo) return 'Africa/Algiers';
	if (60 == so && 120 == wo) return 'Africa/Windhoek';
	if (120 == so && 60 == wo) return 'Europe/Amsterdam';
	if (120 == so && 120 == wo) return 'Africa/Harare';
	if (180 == so && 120 == wo) return 'Europe/Athens';
	if (180 == so && 180 == wo) return 'Africa/Nairobi';
	if (240 == so && 180 == wo) return 'Europe/Moscow';
	if (240 == so && 240 == wo) return 'Asia/Dubai';
	if (270 == so && 210 == wo) return 'Asia/Tehran';
	if (270 == so && 270 == wo) return 'Asia/Kabul';
	if (300 == so && 240 == wo) return 'Asia/Baku';
	if (300 == so && 300 == wo) return 'Asia/Karachi';
	if (330 == so && 330 == wo) return 'Asia/Calcutta';
	if (345 == so && 345 == wo) return 'Asia/Katmandu';
	if (360 == so && 300 == wo) return 'Asia/Yekaterinburg';
	if (360 == so && 360 == wo) return 'Asia/Colombo';
	if (390 == so && 390 == wo) return 'Asia/Rangoon';
	if (420 == so && 360 == wo) return 'Asia/Almaty';
	if (420 == so && 420 == wo) return 'Asia/Bangkok';
	if (480 == so && 420 == wo) return 'Asia/Krasnoyarsk';
	if (480 == so && 480 == wo) return 'Australia/Perth';
	if (540 == so && 480 == wo) return 'Asia/Irkutsk';
	if (540 == so && 540 == wo) return 'Asia/Tokyo';
	if (570 == so && 570 == wo) return 'Australia/Darwin';
	if (570 == so && 630 == wo) return 'Australia/Adelaide';
	if (600 == so && 540 == wo) return 'Asia/Yakutsk';
	if (600 == so && 600 == wo) return 'Australia/Brisbane';
	if (600 == so && 660 == wo) return 'Australia/Sydney';
	if (630 == so && 660 == wo) return 'Australia/Lord_Howe';
	if (660 == so && 600 == wo) return 'Asia/Vladivostok';
	if (660 == so && 660 == wo) return 'Pacific/Guadalcanal';
	if (690 == so && 690 == wo) return 'Pacific/Norfolk';
	if (720 == so && 660 == wo) return 'Asia/Magadan';
	if (720 == so && 720 == wo) return 'Pacific/Fiji';
	if (720 == so && 780 == wo) return 'Pacific/Auckland';
	if (765 == so && 825 == wo) return 'Pacific/Chatham';
	if (780 == so && 780 == wo) return 'Pacific/Enderbury'
	if (840 == so && 840 == wo) return 'Pacific/Kiritimati';
	return 'US/Pacific';
};

var offsetByDate = function(date) {
  if(typeof date == 'undefined' || date == '') {
    offset = "+0000";
  } else {
    var d = Date.parse(date);
    var offset = d.getUTCOffset();
  }
  return offset;
};

var tzMap = function() {
  hash = {
  
    "+0400": "Abu Dhabi",
  
    "+0930": "Adelaide",
  
    "-0900": "Alaska",
  
    "+0600": "Almaty",
  
    "-0800": "America/Los_Angeles",
  
    "-1100": "American Samoa",
  
    "+0100": "Amsterdam",
  
    "-0700": "Arizona",
  
    "+0600": "Astana",
  
    "+0200": "Athens",
  
    "-0400": "Atlantic Time (Canada)",
  
    "+1200": "Auckland",
  
    "-0100": "Azores",
  
    "+0300": "Baghdad",
  
    "+0400": "Baku",
  
    "+0700": "Bangkok",
  
    "+0800": "Beijing",
  
    "+0100": "Belgrade",
  
    "+0100": "Berlin",
  
    "+0100": "Bern",
  
    "-0500": "Bogota",
  
    "-0300": "Brasilia",
  
    "+0100": "Bratislava",
  
    "+1000": "Brisbane",
  
    "+0100": "Brussels",
  
    "+0200": "Bucharest",
  
    "+0100": "Budapest",
  
    "-0300": "Buenos Aires",
  
    "+0200": "Cairo",
  
    "+1000": "Canberra",
  
    "-0100": "Cape Verde Is.",
  
    "-0430": "Caracas",
  
    "+0000": "Casablanca",
  
    "-0600": "Central America",
  
    "-0600": "Central Time (US & Canada)",
  
    "+0530": "Chennai",
  
    "-0700": "Chihuahua",
  
    "+0800": "Chongqing",
  
    "+0100": "Copenhagen",
  
    "+0930": "Darwin",
  
    "+0600": "Dhaka",
  
    "+0000": "Dublin",
  
    "-0500": "Eastern Time (US & Canada)",
  
    "+0000": "Edinburgh",
  
    "+0600": "Ekaterinburg",
  
    "+1200": "Fiji",
  
    "-0400": "Georgetown",
  
    "-0300": "Greenland",
  
    "-0600": "Guadalajara",
  
    "+1000": "Guam",
  
    "+0700": "Hanoi",
  
    "+0200": "Harare",
  
    "-1000": "Hawaii",
  
    "+0200": "Helsinki",
  
    "+1000": "Hobart",
  
    "+0800": "Hong Kong",
  
    "-0500": "Indiana (East)",
  
    "-1100": "International Date Line West",
  
    "+0900": "Irkutsk",
  
    "+0500": "Islamabad",
  
    "+0200": "Istanbul",
  
    "+0700": "Jakarta",
  
    "+0200": "Jerusalem",
  
    "+0430": "Kabul",
  
    "+1200": "Kamchatka",
  
    "+0500": "Karachi",
  
    "+0545": "Kathmandu",
  
    "+0530": "Kolkata",
  
    "+0800": "Krasnoyarsk",
  
    "+0800": "Kuala Lumpur",
  
    "+0300": "Kuwait",
  
    "+0200": "Kyiv",
  
    "-0400": "La Paz",
  
    "-0500": "Lima",
  
    "+0000": "Lisbon",
  
    "+0100": "Ljubljana",
  
    "+0000": "London",
  
    "+0100": "Madrid",
  
    "+1200": "Magadan",
  
    "+1200": "Marshall Is.",
  
    "-0700": "Mazatlan",
  
    "+1000": "Melbourne",
  
    "-0600": "Mexico City",
  
    "-0200": "Mid-Atlantic",
  
    "-1100": "Midway Island",
  
    "+0300": "Minsk",
  
    "+0000": "Monrovia",
  
    "-0600": "Monterrey",
  
    "+0400": "Moscow",
  
    "-0700": "Mountain Time (US & Canada)",
  
    "+0530": "Mumbai",
  
    "+0400": "Muscat",
  
    "+0300": "Nairobi",
  
    "+1100": "New Caledonia",
  
    "+0530": "New Delhi",
  
    "-0330": "Newfoundland",
  
    "+0700": "Novosibirsk",
  
    "+1300": "Nuku'alofa",
  
    "+0900": "Osaka",
  
    "-0800": "Pacific Time (US & Canada)",
  
    "+0100": "Paris",
  
    "+0800": "Perth",
  
    "+1000": "Port Moresby",
  
    "+0100": "Prague",
  
    "+0200": "Pretoria",
  
    "-0500": "Quito",
  
    "+0630": "Rangoon",
  
    "+0200": "Riga",
  
    "+0300": "Riyadh",
  
    "+0100": "Rome",
  
    "+1300": "Samoa",
  
    "-0400": "Santiago",
  
    "+0900": "Sapporo",
  
    "+0100": "Sarajevo",
  
    "-0600": "Saskatchewan",
  
    "+0900": "Seoul",
  
    "+0800": "Singapore",
  
    "+0100": "Skopje",
  
    "+0200": "Sofia",
  
    "+1200": "Solomon Is.",
  
    "+0530": "Sri Jayawardenepura",
  
    "+0400": "St. Petersburg",
  
    "+0100": "Stockholm",
  
    "+1000": "Sydney",
  
    "+0800": "Taipei",
  
    "+0200": "Tallinn",
  
    "+0500": "Tashkent",
  
    "+0400": "Tbilisi",
  
    "+0330": "Tehran",
  
    "-0800": "Tijuana",
  
    "+1300": "Tokelau Is.",
  
    "+0900": "Tokyo",
  
    "+0000": "UTC",
  
    "+0800": "Ulaan Bataar",
  
    "+0800": "Urumqi",
  
    "+0100": "Vienna",
  
    "+0200": "Vilnius",
  
    "+1100": "Vladivostok",
  
    "+0400": "Volgograd",
  
    "+0100": "Warsaw",
  
    "+1200": "Wellington",
  
    "+0100": "West Central Africa",
  
    "+1000": "Yakutsk",
  
    "+0400": "Yerevan",
  
    "+0100": "Zagreb",
  
  };
  return hash;
};

main.js

(function() {
  var datetimePicker;

  $(function() {
    return datetimePicker();
  });

  datetimePicker = function() {
    var end_zone, ends, start_zone, starts;
    starts = $('.datetime.starts_at');
    start_zone = tzMap()[offsetByDate(starts.val())];
    ends = $('.datetime.ends_at');
    end_zone = tzMap()[offsetByDate(ends.val())];
    starts.datetimepicker({
      timeFormat: 'HH:mm z',
      dateFormat: 'yy-mm-dd',
      showTimezone: true,
      timezone: start_zone,
      timezoneList: timezones(),
      stepMinute: 15,
      onClose: function(dateText, inst) {
        var end_date, start_date;
        if (ends.val() !== '') {
          start_date = starts.datetimepicker('getDate');
          end_date = ends.datetimepicker('getDate');
          if (start_date > end_date) {
            return ends.datetimepicker('setDate', start_date);
          }
        } else {

        }
      },
      onSelect: function(selectedDateTime) {
        return ends.datetimepicker('option', 'minDate', starts.datetimepicker('getDate'));
      }
    });
    return ends.datetimepicker({
      timeFormat: 'HH:mm z',
      dateFormat: 'yy-mm-dd',
      showTimezone: true,
      timezone: end_zone,
      timezoneList: timezones(),
      stepMinute: 15,
      onClose: function(dateText, inst) {
        var end_date, start_date;
        if (starts.val() !== '') {
          start_date = starts.datetimepicker('getDate');
          end_date = ends.datetimepicker('getDate');
          if (start_date > end_date) {
            return starts.datetimepicker('setDate', end_date);
          }
        } else {
          return starts.val(dateText);
        }
      },
      onSelect: function(selectedDateTime) {
        return starts.datetimepicker('option', 'maxDate', ends.datetimepicker('getDate'));
      }
    });
  };

}).call(this);