@sytexa/tzdb/lib/getUngroupedTimeZones.js

Always up to date list of time zones, with grouping and major cities

import timeZoneNames from "../time-zones-names.json";

import { getZoneOffset } from "./utils/timeZone.js";

export default function getUngroupedTimeZones(opts) {
  const includeUtc = !!opts && opts.includeUtc;
  const baseZoneName = (opts && opts.baseZone) || "UTC";
  return timeZoneNames
    .reduce(
      function (acc, timeZoneName) {
        const currentOffset = getZoneOffset(timeZoneName);

        // We build on the latest Node.js version, Node.js embed IANA databases
        // it might happen that the environment that will execute getTimeZones() will not know about some
        // timezones. So we ignore the timezone at runtim
        // See https://github.com/vvo/tzdb/issues/43
        if (currentOffset === false) {
          return acc;
        }

        const simpleZone = {
          name: timeZoneName,
          currentTimeOffsetInMinutes: currentOffset,
        };

        acc.push({
          ...simpleZone,
          currentTimeFormat: format(
            simpleZone,
            { baseZoneName },
          ),
        });

        return acc;
      },
      includeUtc ? [utcTimezone] : [],
    )
    .sort((a, b) => {
      return compareNumbers(a, b) || compareStrings(a.name, b.name);
    });
}

function compareNumbers(x, y) {
  return x.currentTimeOffsetInMinutes - y.currentTimeOffsetInMinutes;
}

function compareStrings(x, y) {
  if (typeof x === "string" && typeof y === "string") {
    return x.localeCompare(y);
  }
  return 0;
}

function format(
  { name, currentTimeOffsetInMinutes },
  { baseZoneName = "UTC" },
) {
  const offsetInHours = getOffsetHoursString(currentTimeOffsetInMinutes);

  return `(${baseZoneName} ${offsetInHours}) ${name.replace(/_/g, " ")}`;
}

function getOffsetHoursString(offsetInMinutes) {
  const absOffsetInMinutes = Math.abs(offsetInMinutes);
  const hours = absOffsetInMinutes / 60;

  return `${offsetInMinutes >= 0 ? "+" : "-"}${hours}`;
}

const utcTimezone = {
  name: "UTC",
  currentTimeOffsetInMinutes: 0,
  currentTimeFormat: "(UTC) Coordinated Universal Time",
};