This file contains a list of timezones and their corresponding cities. It also includes functions to get the GMT offset and find the closest timezone based on a target hour.

timezone-finder.js

/**
 * This file contains a list of timezones and their corresponding cities.
 * It also includes functions to get the GMT offset and find the closest timezone based on a target hour.
 */

// Define 24 hour timezones and their cities
const timezones = [
  // Americas (West to East)
  { city: "Honolulu", timezone: "Pacific/Honolulu", gmt: "GMT-10" },
  { city: "Anchorage", timezone: "America/Anchorage", gmt: "GMT-9" },
  { city: "Vancouver", timezone: "America/Vancouver", gmt: "GMT-8" },
  { city: "Los Angeles", timezone: "America/Los_Angeles", gmt: "GMT-8" },
  { city: "Phoenix", timezone: "America/Phoenix", gmt: "GMT-7" },
  { city: "Denver", timezone: "America/Denver", gmt: "GMT-7" },
  { city: "Mexico City", timezone: "America/Mexico_City", gmt: "GMT-6" },
  { city: "Chicago", timezone: "America/Chicago", gmt: "GMT-6" },
  { city: "New York", timezone: "America/New_York", gmt: "GMT-5" },
  { city: "Toronto", timezone: "America/Toronto", gmt: "GMT-5" },
  { city: "Santiago", timezone: "America/Santiago", gmt: "GMT-4" },
  { city: "São Paulo", timezone: "America/Sao_Paulo", gmt: "GMT-3" },

  // Europe/Africa (West to East)
  { city: "Reykjavik", timezone: "Atlantic/Reykjavik", gmt: "GMT+0" },
  { city: "London", timezone: "Europe/London", gmt: "GMT+0" },
  { city: "Paris", timezone: "Europe/Paris", gmt: "GMT+1" },
  { city: "Berlin", timezone: "Europe/Berlin", gmt: "GMT+1" },
  { city: "Cairo", timezone: "Africa/Cairo", gmt: "GMT+2" },
  { city: "Istanbul", timezone: "Europe/Istanbul", gmt: "GMT+3" },
  { city: "Moscow", timezone: "Europe/Moscow", gmt: "GMT+3" },

  // Asia/Oceania (West to East)
  { city: "Dubai", timezone: "Asia/Dubai", gmt: "GMT+4" },
  { city: "Mumbai", timezone: "Asia/Kolkata", gmt: "GMT+5:30" },
  { city: "Bangkok", timezone: "Asia/Bangkok", gmt: "GMT+7" },
  { city: "Singapore", timezone: "Asia/Singapore", gmt: "GMT+8" },
  { city: "Hong Kong", timezone: "Asia/Hong_Kong", gmt: "GMT+8" },
  { city: "Tokyo", timezone: "Asia/Tokyo", gmt: "GMT+9" },
  { city: "Seoul", timezone: "Asia/Seoul", gmt: "GMT+9" },
  { city: "Sydney", timezone: "Australia/Sydney", gmt: "GMT+11" },
  { city: "Auckland", timezone: "Pacific/Auckland", gmt: "GMT+13" },
];

const getGMTOffset = (timezone) => {
  const now = new Date();
  const options = { timeZone: timezone, timeZoneName: "short" };
  const formatter = new Intl.DateTimeFormat("en-US", options);
  const parts = formatter.formatToParts(now);
  const timeZoneName = parts.find((part) => part.type === "timeZoneName").value;

  // Extract the GMT offset from the timeZoneName
  const gmtOffset = timeZoneName.match(/GMT([+-]\d{1,2}(:\d{2})?)/);
  return gmtOffset ? gmtOffset[0] : "GMT";
};

const findTimezoneByHour = (targetHour) => {
  // Get current time
  const now = new Date();

  // Calculate time differences and find closest timezone
  let smallestDifference = 24;
  let closestCity = "";
  let selectedTimezone = "";
  let selectedGmt = "";

  timezones.forEach(({ city, timezone, gmt }) => {
    // Get current hour in this timezone
    const timeInZone = now.toLocaleString("en-US", {
      timeZone: timezone,
      hour: "numeric",
      hour12: false,
      minute: "numeric",
    });

    const currentHour = parseInt(timeInZone);

    // Calculate difference with target hour
    let difference = Math.abs(currentHour - targetHour);

    // Handle cases crossing midnight
    if (difference > 12) {
      difference = 24 - difference;
    }

    // Update closest city if this difference is smaller
    if (difference < smallestDifference) {
      smallestDifference = difference;
      closestCity = city;
      selectedTimezone = timezone;
      selectedGmt = getGMTOffset(timezone);
    }
  });

  return {
    city: closestCity,
    hourDifference: smallestDifference,
    timezone: selectedTimezone,
    gmt: selectedGmt,
  };
};

// Example usage:
console.log(findTimezoneByHour(14)); // Should return a city where it's currently 2 PM

// To test current time in different zones:
// const now = new Date();
// timezones.forEach(({ city, timezone, gmt }) => {
//   const timeInZone = now.toLocaleString("en-US", {
//     timeZone: timezone,
//     hour: "numeric",
//     minute: "numeric",
//     hour12: true,
//   });
//   console.log(`Current time in ${city}: ${timeInZone} ${gmt}`);
// });