How to use the log4js.addAppender function in log4js

function initLogger(options) {
    var customLoggingAppender = options['customServiceLogger'];

    if ( customLoggingAppender ) {
        // clear the default appender(s)
        log4js.clearAppenders();

        //
        log4js.addAppender(customLoggingAppender, 'jive-sdk');
    }

    var logfile = options['logFile'] || options['logfile'];
    var logLevel = process.env['jive_logging_level'] || options['logLevel'] || options['loglevel'] || 'INFO';
    logLevel = logLevel.toUpperCase();

    if (logfile) {
        if (logfile.indexOf('logs/') === 0) {
            if (!fs.existsSync('logs')) {
                jive.logger.warn('logs subdirectory does not exist. Creating directory now.');
                fs.mkdirSync('logs');
            }
        }

        var logFileSize = options['logFileSize'] || undefined;
        var logFileNumBackups = options['logFileNumBackups'] || undefined;

var settings = require('./settings'),
    UrlProvider = require('./urlprovider-mongo').UrlProvider,
//    UserProvider = require('./urlprovider-memory').UserProvider,
    sys = require('sys'),
    template = require('./template/template'),
    loader = require('./template/loader'),
    admin = require('./admin');

loader.set_path(settings.template_path);

/*
 * LOGGING SUPPORT
 */
var log4js = require('log4js');
log4js.addAppender(log4js.consoleAppender(), 'app');
log4js.addAppender(log4js.consoleAppender(), 'resolved');
log4js.addAppender(log4js.consoleAppender(), 'defer_queue');

app_log = log4js.getLogger('app');
app_log.setLevel('TRACE');

resolved_log = log4js.getLogger('resolved');
resolved_log.setLevel('TRACE');

defer_log = log4js.getLogger('defer_queue');
defer_log.setLevel('TRACE');

// error handling
function handleError(error, res) {
    app_log.error(error.message);
    app_log.debug(JSON.stringify(error));

// return thresholded appender
    return log4js.appenders.logLevelFilter(level, appender);
  }

  //
  // clear default loggers
  //

  log4js.clearAppenders();

  //
  // configure console logger for non-production environment only
  //

  if ('production' !== N.runtime.env) {
    log4js.addAppender(log4js.appenders.console());
  }

  //
  // leave only loggers (with appenders) configs, removing keywords
  //

  delete config.options;

  //
  // configure logger categories and appenders
  //

  _.each(config, function (loggerConfig, name) {
    _.each(loggerConfig, function (appenderConfig) {
      var filename, appender;

before(function(done) {
    var config = { esclient: mockElasticsearchClient, buffersize: 1 };
    log4js.clearAppenders();
    log4js.addAppender(log4jsElasticSearch.configure(config, null, done), 'unittest');
  });
  it("Must have created the template", function() {

before(function(done) {
    var config = {
      typeName: 'log4js',
      buffersize: 1,
      url: process.env.ES_URL,
      layout: {
        type: 'logstash'
      }
    };
    log4js.clearAppenders();
    log4js.addAppender(log4jsElasticSearch.configure(config, null, done), 'unittest');
  });

function getLogger(dir){
    log4js.loadAppender('file');
    log4js.appenders['TASK'] = [];
    var appender = log4js.appenders.file(dir + "/tast.log");
    if(log4js.hasLogger("TASK")){
        log4js.getLogger('TASK').removeAllListeners();
    }
    log4js.addAppender(appender,'TASK');
    return log4js.getLogger('TASK');
}

const logFile = log4js.appenders.file(
  path.join(__dirname, conf.logger.relativePath)
);

log4js.addLogger = name => {
  if (!set.has(name)) {
    set.add(name);
    log4js.addAppender(logFile, name);
  }
  return log4js.getLogger(name);
};

const signupFile = log4js.appenders.file(
  path.join(__dirname, '/../logs/signuplog.log')
);
log4js.addAppender(signupFile, 'signup');