code: function toLocalIsoString(date, includeMillis) {
      if (includeMillis === undefined) {
          includeMillis = false;
      }
      const pad = (n, length, padChar) => {
          if (length === undefined) { length = 2; }
          if (padChar === undefined) { padChar = "0"; }
          let str = "" + n;
          while (str.length < length) {
              str = padChar + str;
          }
          return str;
      };
      const getOffsetFromUTC = () => {
          const offset = date.getTimezoneOffset();
          if (offset === 0) {
              return "Z";
          }
          return (offset < 0 ? "+" : "-")
              + pad(Math.abs(offset / 60), 2) + ":"
              + pad(Math.abs(offset % 60), 2);
      };
      return date.getFullYear() + "-"
          + pad(date.getMonth() + 1) + "-"
          + pad(date.getDate()) + "T"
          + pad(date.getHours()) + ":"
          + pad(date.getMinutes()) + ":"
          + pad(date.getSeconds())
          + (includeMillis ? "." + pad(date.getMilliseconds(), 3) : "")
          + getOffsetFromUTC();
  }
docs: Returns a string in ISO 8601 format including timezone offset information.
  @param date a Date object
  @param includeMillis whether to include milliseconds in the string (defaults to false)