code: function writeLog(logLevel, writeArgs) {
  
          var logName = loggerName || 'ROOT';
          var levelAppenders = [];
          var logger;
  
          // child level always overwrite parent levels
          // if the child does not allow, no appender even parents' ones won't show
          if (getLevelNumber(thisLogger.getLevel()) <= getLevelNumber(logLevel)) {
              logger = thisLogger;
              while (logger) {
                  levelAppenders = _.concat(levelAppenders, logger.getAppenders()); logger = logger.getParent();
              }
          }
  
          // write the message to each appender no more than once!
          _.uniq(levelAppenders).forEach(function (appender) {
  
              var fmt = appender.pattern.format(logName, logLevel, writeArgs[0], _.slice(writeArgs, 1));
  
              var args = _.concat(logName, logLevel, fmt.message);
              // any more arguments ?
              if (fmt.otherArgs) {
                  args = _.concat(args, fmt.otherArgs);
              }
              appender.writeLog.apply(this, args);
          });
      }
docs: write a log entry to all appenders.
  
  All parent loggers will be checked to see if their appenders - if any - should write the log.
  
  Up to the rootLogger.