code: function isIso8601DateString(value) {
      var regex = /^([+-]\d{6}|\d{4})(-(0[1-9]|1[0-2])(-(0[1-9]|[12]\d|3[01]))?)?$/;
  
      // Verify that it's in ISO 8601 format (via the regex) and that it represents a valid day (via Date.parse)
      return regex.test(value) && !isNaN(Date.parse(value));
    }
docs: Check that a given value is a valid ISO 8601 date string without time and time zone components