code: function isDayFirst() {
    if (dayFirst !== null) {
      return dayFirst;
    }
  
    if (!('Intl' in window)) {
      return false;
    }
  
    const options = { day: 'numeric', month: 'short' };
    const formatter = new window.Intl.DateTimeFormat(undefined, options);
    const output = formatter.format(new Date(0));
  
    dayFirst = !!output.match(/^\d/);
    return dayFirst;
  }
docs: Private: Determine if the day should be formatted before the month name in the user's current locale. For example, `9 Jun` for en-GB and `Jun 9` for en-US.  Returns true if the day appears before the month.