date-fns/_lib/getTimezoneOffsetInMilliseconds.mjs

Modern JavaScript date utility library

/**
 * Google Chrome as of 67.0.3396.87 introduced timezones with offset that includes seconds.
 * They usually appear for dates that denote time before the timezones were introduced
 * (e.g. for 'Europe/Prague' timezone the offset is GMT+00:57:44 before 1 October 1891
 * and GMT+01:00:00 after that date)
 *
 * Date#getTimezoneOffset returns the offset in minutes and would return 57 for the example above,
 * which would lead to incorrect calculations.
 *
 * This function returns the timezone offset in milliseconds that takes seconds in account.
 */
export function getTimezoneOffsetInMilliseconds(date) {
  const utcDate = new Date(
    Date.UTC(
      date.getFullYear(),
      date.getMonth(),
      date.getDate(),
      date.getHours(),
      date.getMinutes(),
      date.getSeconds(),
      date.getMilliseconds(),
    ),
  );
  utcDate.setUTCFullYear(date.getFullYear());
  return date.getTime() - utcDate.getTime();
}