List all strange timezones for your locale (JS)

list-strange-timezones.js

const showStrangeTimezonesForMyLocale = (yearFrom, yearTo) => {
  if (yearFrom > yearTo) {
    throw new Error("yearFrom must not be greater than yearTo");
  }
  const correctTimezone = new Date().getTimezoneOffset();
  const fullSearchCount = yearTo - yearFrom + 1;
  console.log("Correct timezone is:", correctTimezone, "(offset minutes)");
  console.log(
    "searching years\nfrom:",
    yearFrom,
    ",",
    "to:",
    yearTo,
    ",",
    "count:",
    fullSearchCount,
    "\n\n"
  );

  const results =
    // : {
    //   rangeInclLeftInclRight: [number, number];
    //   count: number;
    //   timezone: number;
    // }[]
    [];

  const recentRange = {
    start: yearFrom,
    tz: new Date(Date.UTC(yearFrom, 4)).getTimezoneOffset(),
  };

  for (let year = yearFrom + 1; year <= yearTo; year += 1) {
    const currTz = new Date(Date.UTC(year, 4)).getTimezoneOffset();

    if (currTz !== recentRange.tz) {
      if (recentRange.tz !== correctTimezone) {
        results.push({
          rangeInclLeftInclRight: [recentRange.start, year - 1],
          count: year - recentRange.start,
          timezone: recentRange.tz,
        });
      }
      recentRange.start = year;
      recentRange.tz = currTz;
    }
  }

  if (recentRange.tz !== correctTimezone) {
    results.push({
      rangeInclLeftInclRight: [recentRange.start, yearTo],
      count: yearTo - recentRange.start + 1,
      timezone: recentRange.tz,
    });
  }

  results.forEach((x) => {
    console.log(
      `from: ${x.rangeInclLeftInclRight[0]}, to: ${x.rangeInclLeftInclRight[1]} --> count: ${x.count}, strange timezone: ${x.timezone}`
    );
  });

  const fullCountOfStrange = results.reduce(
    (accu, curr) => accu + curr.count,
    0
  );

  console.log(
    "\nFull count of years with strange timezone:",
    fullCountOfStrange,
    `(${((100 * fullCountOfStrange) / fullSearchCount).toFixed(
      2
    )}% of ${fullSearchCount})`,
    "\n"
  );
};

showStrangeTimezonesForMyLocale(1, 2024);