Scheduling meetings across time zones

Coordinating meetings across different time zones can be a logistical headache. It requires switching between apps and doing mental calculations to convert time zones, which is tedious and prone to errors. Streamline this process with Slack!

Using Workflow Builder, we'll create an automation that takes a proposed meeting time in your timezone, converts it to the timezone of the person you’re scheduling with, and schedules the meeting.

Your timezone scheduler workflow will consist of the following steps:

1. Built-in function: Collect info in a form
2. Custom function: Timezone-aware meeting schedule
3. Built-in function: Send a message with the time conversion and a button to create the calendar invite
4. Calendar connector: Use the Google Calendar connector to create the meeting
5. Built-in function: Reply with a message in thread with the confirmation of the meeting creation

Get started

Set up tools

We are using the Slack CLI and Deno Slack SDK to create an app where the custom function exists and can be pulled into Workflow Builder to be used as a step. You should be familiar with the Slack CLI and how it works before going further. If this is new for you, we recommend starting with the Hello world app first.

Create the project

Navigate to a directory where you have permission to create new files. Using the Slack CLI, run the following command to create a new project from a template:

slack create time-zone-app --template slack-samples/deno-blank-template

This creates your project from a blank template. After that, navigate to your project folder.

cd time-zone-app

Open the project in VSCode.

code .

Code the app

Update the manifest

The app manifest is where your app's configurations are stored. Navigate to the manifest.ts file in your project and replace the template code with what is shown here.

import { Manifest } from "deno-slack-sdk/mod.ts";

/**
 * The app manifest contains the app's configuration. This
 * file defines attributes like app name and description.
 */
export default Manifest({
  name: "Time zone scheduler",
  description: "Assists in scheduling meetings across time zones",
  icon: "app_icon.png",
  functions: [],
  workflows: [],
  outgoingDomains: ["timeapi.io"],
  botScopes: ["commands", "chat:write", "chat:write.public"],
});

We're going to be creating a custom function to be used as a workflow step in Workflow Builder, so we need to declare that in the manifest. Add this import to the top of the file:

import { TimeZoneSchedulerFunction } from "./functions/timezone_scheduler_function.ts";

In the functions object, add the function reference, like this:

functions: [TimeZoneSchedulerFunction],

Additionally, use the icon of your choice and update the reference in the icon property. It is a required field. Save your changes.

Code the custom function

A custom function in Slack requires two components: the function definition, DefineFunction, and the function logic, SlackFunction. Create a new folder in your project named functions, then create a file in that folder named timezone_scheduler_function.ts. Copy and paste the code below into the new file, then save it.

import { DefineFunction, Schema, SlackFunction } from "deno-slack-sdk/mod.ts";

// Function definition
export const TimeZoneSchedulerFunction = DefineFunction({
  callback_id: "time_zone_scheduler",
  title: "Time Zone-Aware Meeting Scheduler",
  description:
    "Converts a proposed meeting time to the participant's time zone and calculates the end time.",
  source_file: "functions/timezone_scheduler_function.ts",
  input_parameters: {
    properties: {
      meeting_time: {
        type: Schema.types.string,
        description:
          "Proposed meeting time (e.g., '2023-08-12T14:30:00Z' or 'Aug 12, 2023, 2:30:00 PM')",
      },
      user_timezone: {
        type: Schema.types.string,
        description:
          "User's local date and time with timezone (e.g., 'August 14th, 2024 at 11:06 PM GMT+2')",
      },
      from_timezone: {
        type: Schema.types.string,
        description:
          "Time zone of the user who proposed the meeting (e.g., 'America/New_York')",
      },
      target_timezone: {
        type: Schema.types.string,
        description:
          "Time zone of the meeting participant (e.g., 'Europe/London')",
      },
      duration_minutes: {
        type: Schema.types.number,
        description: "The duration of the meeting in minutes"
      }
    },
    required: [
      "meeting_time",
      "user_timezone",
      "from_timezone",
      "target_timezone",
      "duration_minutes"
    ],
  },
  output_parameters: {
    properties: {
      readable_time_origin: {
        type: Schema.types.string,
        description: "Readable meeting time in the user's time zone",
      },
      readable_time_participant: {
        type: Schema.types.string,
        description: "Readable meeting time in the participant's time zone",
      },
      calendar_meeting_time: {
        type: Schema.slack.types.timestamp,
        description: "Meeting time in the user's timezone",
      },
      calendar_end_time: {
        type: Schema.slack.types.timestamp,
        description: "Ending meeting time"
      }
    },
    required: [
        "readable_time_origin",
        "readable_time_participant",
        "calendar_meeting_time",
        "calendar_end_time"
    ],
  },
});

export default SlackFunction(
  TimeZoneSchedulerFunction,
  async ({ inputs }) => {

    let readableTimeOrigin: string | null = null;
    let readableTimeParticipant: string | null = null;
    let calendarMeetingTime: number | null = null;
    let calendarEndTime: number | null = null;

    try {
      // Step 1: Correctly format the meeting time for API usage
      const formattedMeetingTime = formatDateTimeForAPI(
        inputs.meeting_time,
      );

      const meetingConversionResult = await convertTimeZone(
        inputs.from_timezone,
        formattedMeetingTime,
        inputs.target_timezone,
      );

      if (
        !meetingConversionResult ||
        !meetingConversionResult.conversionResult
      ) {
        throw new Error("Invalid DateTime format from API.");
      }

      // Step 2: Convert meeting_time from from_timezone to user timezone
      const calendarConversionResult = await convertTimeZone(
        inputs.from_timezone,
        formattedMeetingTime,
        inputs.user_timezone,
      );

      if (
        !calendarConversionResult || !calendarConversionResult.conversionResult
      ) {
        throw new Error("Invalid DateTime format from API.");
      }

      // Extract the calendar meeting time in user's timezone
      const userTimeZoneDate = new Date(
        calendarConversionResult.conversionResult.dateTime,
      );
      calendarMeetingTime = Math.floor(userTimeZoneDate.getTime() / 1000);

      // Step 4: Calculate readable times
      const originTime = new Date(inputs.meeting_time);
      readableTimeOrigin = originTime.toLocaleString("en-US", {
        hour: "numeric",
        minute: "numeric",
        hour12: true,
      });

      const participantDateTime = new Date(
        meetingConversionResult.conversionResult.dateTime,
      );
      readableTimeParticipant = participantDateTime.toLocaleString("en-US", {
        hour: "numeric",
        minute: "numeric",
        hour12: true,
      });

      // Step 5: Calculate end time for user
      const endTimeUser = new Date(
        userTimeZoneDate.getTime() + inputs.duration_minutes * 60000,
      );
      calendarEndTime = Math.floor(endTimeUser.getTime() / 1000);
    } catch (error) {
      return {
        error: `Error converting time: ${error.message}`,
      };
    }

    return {
      outputs: {
        readable_time_origin: readableTimeOrigin,
        readable_time_participant: readableTimeParticipant,
        calendar_meeting_time: calendarMeetingTime,
        calendar_end_time: calendarEndTime,
      },
    };
  },
);

You may notice in the function logic, we call a couple of helper functions: formatDateTimeForAPI and convertTimeZone. We'll create those function files next.

Add support files

There are a few other files we need to support this app; we will create them now.

Add a new folder to the project named util. Create a file in that folder named api_date_formatter.ts. This file will help to parse and format dates. Copy and paste the following code into the file, then save.

 export const formatDateTimeForAPI = (dateTimeString: string): string => {
  const date = new Date(dateTimeString);
  if (isNaN(date.getTime())) {
    throw new Error(`Invalid date format: ${dateTimeString}`);
  }
  const year = date.getFullYear();
  const month = String(date.getMonth() + 1).padStart(2, "0");
  const day = String(date.getDate()).padStart(2, "0");
  const hours = String(date.getHours()).padStart(2, "0");
  const minutes = String(date.getMinutes()).padStart(2, "0");
  const seconds = String(date.getSeconds()).padStart(2, "0");

  return `${year}-${month}-${day} ${hours}:${minutes}:${seconds}`;
}

Create another file in the util folder and name it convert_timezone.ts. This file converts the from time zone to the to time zone. Copy and paste the following code into it, then save.

/**
 * Converts a given date and time from one timezone to another using the Time API.
 * @param fromTimeZone - The original timezone of the date and time.
 * @param dateTime - The date and time to be converted.
 * @param toTimeZone - The target timezone for the conversion.
 * @returns A promise that resolves to the converted date and time result.
 */

export async function convertTimeZone(
  fromTimeZone: string,
  dateTime: string,
  toTimeZone: string
): Promise<any> {
  try {
    const response = await fetch(
      "https://timeapi.io/api/Conversion/ConvertTimeZone",
      {
        method: "POST",
        headers: {
          accept: "application/json",
          "Content-Type": "application/json",
        },
        body: JSON.stringify({
          fromTimeZone,
          dateTime,
          toTimeZone,
          dstAmbiguity: "",
        }),
      }
    );

    if (!response.ok) {
      throw new Error("Failed to convert time zone");
    }

    const data = await response.json();
    return data;
  } catch (error) {
    console.error("Error during time zone conversion:", error);
    throw error;
  }
}

Be sure to add the imports for these files to the top of the timezone_scheduler_function.ts file, like this:

import { formatDateTimeForAPI } from "../util/api_date_formatter.ts";
import { convertTimeZone } from "../util/convert_timezone.ts";

Create one more file in the util folder and name it timezones.txt. This is the full list of available time zones. Copy and paste the following text into it, then save the file.

Time zones

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

The last file we'll create is a slack.json file. Create this in the project (the root of the project, not within folder) and paste the code here into it, then save:

{
  "hooks": {
    "get-hooks": "deno run -q --allow-read --allow-net https://deno.land/x/deno_slack_hooks@1.3.1/mod.ts"
  }
}

This allows your app to access an external source - the time conversion API.

Run the app

In your terminal window, run the following command:

slack run

Select the workspace you'd like to run the app in. If successful, you'll see a message that says Connected awaiting events.

Build the workflow in Workflow Builder

To create a new workflow, you will need to open Workflow Builder in Slack. You can open Workflow Builder using one of the following methods.

• Use the message box: In any channel, type /workflow and select Create a workflow.
• Use the sidebar: Navigate to the left sidebar in Slack and click More, then Tools, then Workflows. Click +New then Build Workflow to create a new workflow.

Under Start the workflow..., click Choose an event, then select From a link in Slack.

The first step of the workflow is to collect info in a form.

• Click the button to continue, then select Add steps to Collect info in a form.
• Give the form a name, like Time zone scheduler, and click + Add question. Enter From which time zone? as the question and use Short answer for the Question type. Click Done.
• Repeat the process for adding the following questions and types:
  • Date and time of the meeting? → date/time picker
  • How long is your meeting (in minutes)? → number
  • To which time zone? → short answer
  • What is your meeting about? → short answer
  • Email of your contact → short answer
  • Your time zone when running the workflow → short answer

Save the form.

Add custom function

With your custom function now available in Workflow Builder (after running slack run), add it as the second step in the workflow by clicking + Add steps, then searching for your app by name in the left sidebar search. Select Time Zone-Aware Meeting Scheduler as the step.

We need to connect the info we collected on the previous step to pass it as input of our function. For that we’re going to use variables. Click on the {} on the right side of the inputs and choose the following:

• Meeting time: {}Answer to: Date and time of the meeting? Then click on the caret and choose the local compact format (that’s the format we expect in the code of our custom function).
• User timezone: {}Answer to: Your timezone when running the workflow
• From timezone: {}Answer to: From which timezone
• Target timezone: {}Answer to: To which timezone
• Duration in minutes: {}Answer to: How long is your meeting (in minutes)?

Save your changes.

Send a message

Now, inform the user of the time conversion results. Add another step to the workflow and in the sidebar, search for Messages > Send a message to a person.

You can craft your own message using all the variables available from previous steps. Here’s an example:

Enable the Include a button option and customize the button label. The workflow will pause here and continue once the user clicks the button. Save your changes to continue.

Use the Google Calendar connector

Add another step to the workflow and in the sidebar, search for Google Calendar > Create a calendar event > Add just the step. Confirm by clicking the Set Up button. Fill in the event details using the variables from previous steps.

Confirm with a message in thread

To finish, let the user know the event has been successfully scheduled. Add another step to the workflow and in the sidebar, search for Messages > Reply to a message in thread.

Using the available variables, craft a message that says: Calendar invite sent for {} Answer to: What's your meeting about?. You can see it here {} Event link .

Where {} Answer to: What's your meeting about? and {} Event link are variables added by clicking the variable button.

Test your function

Your workflow is now complete! Click the Finish Up button in Workflow Builder, name your workflow, click Publish, and copy the generated link trigger. Share the link in your test Slack channel or add it as a bookmark or to your channel canvas.

Deploy your function

In the process of developing your function, you ran it on your local machine. As soon as you shut that environment down or turn off your computer, the function will stop running. Deploying your function to infrastructure managed by Slack ensures that the function is always available.

To deploy your function to production, run:

slack deploy

Choose the appropriate workspace for deployment. Remember, the local version (slack run) and the production version (slack deploy) are separate. Update Workflow Builder to use the production function and reconnect input variables.