code: function isYearSeparator() {
    if (yearSeparator !== null) {
      return yearSeparator;
    }
  
    if (!('Intl' in window)) {
      return true;
    }
  
    const options = { day: 'numeric', month: 'short', year: 'numeric' };
    const formatter = new window.Intl.DateTimeFormat(undefined, options);
    const output = formatter.format(new Date(0));
  
    yearSeparator = !!output.match(/\d,/);
    return yearSeparator;
  }
docs: Private: Determine if the year should be separated from the month and day with a comma. For example, `9 Jun 2014` in en-GB and `Jun 9, 2014` in en-US.  Returns true if the date needs a separator.