code: function(loggingEvent)
  	{
  		var retval;
  		switch (loggingEvent.level) {	
  			case Log4js.Level.FATAL:
  				retval = 2;//nsIScriptError.exceptionFlag = 2
  				break;
  			case Log4js.Level.ERROR:
  				retval = 0;//nsIScriptError.errorFlag
  				break;
  			case Log4js.Level.WARN:
  				retval = 1;//nsIScriptError.warningFlag = 1
  				break;
  			default:
  				retval = 1;//nsIScriptError.warningFlag = 1
  				break;
  		}
  		
  		return retval;		
  	}
docs: Map Log4js.Level to jsConsole Flags:
  <ul>
  <li>nsIScriptError.errorFlag (0) = Level.Error</li>
  <li>nsIScriptError.warningFlag (1)= Log4js.Level.WARN</li>
  <li>nsIScriptError.exceptionFlag (2) = Log4js.Level.FATAL</li>
  <li>nsIScriptError.strictFlag (4) = unused</li>
  </ul>
  @private