code: function formatFn(date, level, fnLabel, msgArgs) {
           const l = (fnLabel === null || fnLabel === undefined) ? '' : ` ${fnLabel}`;
           return `${date.toISOString()} ${level}${l}: ${joinMsgArgs(msgArgs)}`;
       }
docs: The default log formatting.  This can overriden by the user by using
  `log.setFormatFunction()`.
  
  @param  {Date} date             - The date the message was created.
  @param  {string} level          - The current log level.
  @param  {string} [fnLabel]      - The label that we are logging to.
  @param  {Array.<*>} [msgArgs] - The multiple message parameters.
  @returns {string}               - The formatted message to print.
  @private