JavaScript function mapping IANA time znoe names to UTC offsets in minutes. Originally intended for Cloudfront Functions

timezone-to-offset.js

const offsets = [
  -720, -660, -600, -570, -540, -480, -420, -360, -300, -240, -210, -180,
  -150, -120, -60, 0, 60, 120, 180, 210, 240, 270, 300, 330, 345, 360,
  390, 420, 480, 525, 540, 570, 600, 630, 660, 720, 765, 780, 840
];

const zones = {
  Africa: {
    15: 'Abidjan Accra Bamako Banjul Bissau Conakry Dakar Freetown Lome Monrovia Nouakchott Ouagadougou Sao_Tome Timbuktu',
    16: 'Algiers Bangui Brazzaville Casablanca Ceuta Douala El_Aaiun Kinshasa Lagos Libreville Luanda Malabo Ndjamena Niamey Porto-Novo Tunis',
    17: 'Blantyre Bujumbura Cairo Gaborone Harare Johannesburg Juba Khartoum Kigali Lubumbashi Lusaka Maputo Maseru Mbabane Tripoli Windhoek',
    18: 'Addis_Ababa Asmara Asmera Dar_es_Salaam Djibouti Kampala Mogadishu Nairobi'
  },
  America: {
    2: 'Adak Atka', 4: 'Anchorage Juneau Metlakatla Nome Sitka Yakutat', 5: 'Ensenada Los_Angeles Santa_Isabel Tijuana Vancouver',
    6: 'Boise Cambridge_Bay Creston Dawson Dawson_Creek Denver Edmonton Fort_Nelson Hermosillo Inuvik Mazatlan Ojinaga Phoenix Shiprock Whitehorse Yellowknife',
    7: 'Bahia_Banderas Belize Chicago Costa_Rica El_Salvador Guatemala Indiana/Knox Indiana/Tell_City Knox_IN Managua Matamoros Menominee Merida Mexico_City Monterrey North_Dakota/Beulah North_Dakota/Center North_Dakota/New_Salem Rainy_River Rankin_Inlet Regina Resolute Swift_Current Tegucigalpa Winnipeg',
    8: 'Atikokan Bogota Cancun Cayman Coral_Harbour Detroit Eirunepe Fort_Wayne Grand_Turk Havana Indiana/Indianapolis Indiana/Marengo Indiana/Petersburg Indiana/Vevay Indiana/Vincennes Indiana/Winamac Indianapolis Iqaluit Jamaica Kentucky/Louisville Kentucky/Monticello Lima Louisville Montreal Nassau New_York Nipigon Panama Pangnirtung Port-au-Prince Porto_Acre Rio_Branco Thunder_Bay Toronto',
    9: 'Anguilla Antigua Aruba Asuncion Barbados Blanc-Sablon Boa_Vista Campo_Grande Caracas Cuiaba Curacao Dominica Glace_Bay Goose_Bay Grenada Guadeloupe Guyana Halifax Kralendijk La_Paz Lower_Princes Manaus Marigot Martinique Moncton Montserrat Port_of_Spain Porto_Velho Puerto_Rico Santiago Santo_Domingo St_Barthelemy St_Kitts St_Lucia St_Thomas St_Vincent Thule Tortola Virgin',
    10: 'St_Johns', 11: 'Araguaina Bahia Belem Buenos_Aires Catamarca Cordoba Cayenne Fortaleza Godthab Jujuy Maceio Mendoza Miquelon Montevideo Nuuk Paramaribo Punta_Arenas Recife Rosario Santarem Sao_Paulo Stanley',
    13: 'Noronha', 14: 'Scoresbysund', 15: 'Danmarkshavn',
    Argentina: { 11: 'Buenos_Aires Catamarca ComodRivadavia Cordoba Jujuy La_Rioja Mendoza Rio_Gallegos Salta San_Juan San_Luis Tucuman Ushuaia' }
  },
  Antarctica: {
    11: 'Palmer Rothera', 15: 'Troll', 18: 'Syowa', 22: 'Mawson', 25: 'Vostok', 27: 'Davis',
    32: 'DumontDUrville Macquarie', 34: 'Casey', 35: 'McMurdo South_Pole GMT+12'
  },
  Asia: {
    17: 'Beirut Famagusta Gaza Hebron Jerusalem Nicosia Tel_Aviv', 18: 'Aden Amman Baghdad Bahrain Damascus Djibouti Istanbul Kuwait Qatar Riyadh',
    19: 'Tehran', 20: 'Baku Dubai Muscat Tbilisi Yerevan', 21: 'Kabul',
    22: 'Aqtau Aqtobe Ashgabat Ashkhabad Atyrau Dushanbe Karachi Oral Qyzylorda Samarkand Tashkent Yekaterinburg',
    23: 'Calcutta Colombo Kolkata', 24: 'Kathmandu Katmandu',
    25: 'Almaty Bishkek Dacca Dhaka Kashgar Omsk Qostanay Thimbu Thimphu Urumqi', 26: 'Rangoon Yangon',
    27: 'Bangkok Barnaul Ho_Chi_Minh Hovd Jakarta Krasnoyarsk Novokuznetsk Novosibirsk Phnom_Penh Pontianak Saigon Tomsk Vientiane',
    28: 'Brunei Choibalsan Chongqing Chungking Hong_Kong Irkutsk Kuala_Lumpur Kuching Macao Macau Makassar Manila Shanghai Singapore Taipei Ulaanbaatar Ulan_Bator',
    30: 'Dili Jayapura Khandyga Pyongyang Seoul Tokyo Yakutsk', 32: 'Chita Ust-Nera Vladivostok',
    34: 'Magadan Sakhalin Srednekolymsk', 35: 'Anadyr Kamchatka'
  },
  Atlantic: { 9: 'Bermuda', 11: 'Stanley', 13: 'South_Georgia', 14: 'Azores Cape_Verde', 15: 'Canary Faeroe Faroe Madeira Reykjavik St_Helena', 16: 'Jan_Mayen' },
  Australia: { 28: 'Perth West', 29: 'Eucla', 31: 'Adelaide Broken_Hill Darwin North South Yancowinna', 32: 'ACT Brisbane Canberra Currie Hobart Lindeman Melbourne NSW Queensland Sydney Tasmania Victoria', 33: 'LHI Lord_Howe' },
  Brazil: { 8: 'Acre', 9: 'West', 11: 'East', 13: 'DeNoronha' },
  Canada: { 5: 'Pacific', 6: 'Mountain Yukon', 7: 'Central Saskatchewan', 8: 'Eastern', 9: 'Atlantic', 10: 'Newfoundland' },
  Chile: { 7: 'EasterIsland', 9: 'Continental' },
  Etc: {
    0: 'GMT+11', 1: 'GMT+10', 6: 'GMT+9', 7: 'GMT+8', 8: 'GMT+7', 9: 'GMT+6', 10: 'GMT+5', 11: 'GMT+4', 12: 'GMT+3', 13: 'GMT+2', 14: 'GMT+1',
    15: 'GMT GMT+0 GMT-0 GMT0 Greenwich UCT UTC Universal Zulu', 16: 'GMT-1', 17: 'GMT-2', 18: 'GMT-3', 20: 'GMT-4', 22: 'GMT-5', 25: 'GMT-6', 27: 'GMT-7', 28: 'GMT-8', 30: 'GMT-9',
    32: 'GMT-10', 34: 'GMT-11', 35: 'GMT-12 GMT+12', 37: 'GMT-13', 38: 'GMT-14'
  },
  Europe: {
    15: 'Belfast Guernsey Isle_of_Man Jersey Lisbon London',
    16: 'Amsterdam Andorra Belgrade Berlin Bratislava Brussels Budapest Busingen Copenhagen Dublin Gibraltar Ljubljana Luxembourg Madrid Malta Monaco Oslo Paris Podgorica Prague Rome San_Marino Sarajevo Skopje Stockholm Tirane Vaduz Vatican Vienna Warsaw Zagreb Zurich',
    17: 'Athens Bucharest Chisinau Famagusta Helsinki Kaliningrad Kiev Mariehamn Nicosia Riga Sofia Tallinn Tiraspol Uzhgorod Vilnius Zaporozhye',
    18: 'Istanbul Kirov Minsk Moscow Simferopol Volgograd', 20: 'Astrakhan Samara Saratov Ulyanovsk'
  },
  Indian: { 18: 'Antananarivo Comoro Mayotte', 20: 'Mahe Mauritius Reunion', 22: 'Kerguelen Maldives', 25: 'Chagos', 26: 'Cocos', 27: 'Christmas' },
  Mexico: { 5: 'BajaNorte', 6: 'BajaSur', 7: 'General' },
  Pacific: {
    '-1': 'GMT+12', 1: 'Midway Niue Pago_Pago Samoa', 2: 'Honolulu Johnston Rarotonga Tahiti', 3: 'Marquesas', 4: 'Gambier', 5: 'Pitcairn', 7: 'Easter Galapagos',
    30: 'Palau', 32: 'Chuuk Guam Port_Moresby Saipan Truk Yap', 34: 'Bougainville Efate Guadalcanal Kosrae Norfolk Noumea Pohnpei Ponape',
    35: 'Auckland Fiji Funafuti Kwajalein Majuro Nauru Tarawa Wake Wallis', 36: 'Chatham', 37: 'Apia Enderbury Fakaofo Kanton Tongatapu', 38: 'Kiritimati'
  },
  US: { 2: 'Aleutian Hawaii', 4: 'Alaska', 5: 'Pacific', 6: 'Arizona Mountain', 7: 'Central Indiana-Starke', 8: 'East-Indiana Eastern Michigan', 1: 'Samoa' },
  2: 'HST', 5: 'PST8PDT', 6: 'MST MST7MDT Navajo', 7: 'CST6CDT', 8: 'Cuba EST EST5EDT Jamaica', 15: 'GB GB-Eire GMT GMT+0 GMT-0 GMT0 Greenwich Iceland Portugal UCT UTC Universal WET Zulu',
  16: 'Arctic/Longyearbyen Atlantic/Jan_Mayen CET Eire MET Poland', 17: 'EET Egypt Israel Libya', 18: 'Asia/Istanbul Europe/Istanbul Turkey W-SU',
  19: 'Iran', 28: 'Hongkong PRC ROC Singapore', 30: 'Japan ROK', 35: 'Kwajalein NZ', 36: 'NZ-CHAT'
};

function getUtcOffset(tz) {
  const parts = tz.split('/');
  const city = parts.pop();
  let node = zones;

  for (let i = 0, e = parts.length; i < e; i++) {
    node = node[parts[i]];
    if (!node) return 0;
  }

  for (const key in node) {
    const val = node[key];
    if (typeof val === 'string' && (' ' + val + ' ').indexOf(' ' + city + ' ') !== -1) {
      return offsets[key];
    }
  }

  return 0;
}