How to use the log4js.debug function in log4js

proxy = Proxies.nextProxy(url.host, function(err, proxy) {
    if(err) {
      if(err === 'ALL_BLOCKED') {
        res.status(503).end('all proxies are blocked')
      } else {
        res.status(503).end('all proxies are broken')
      }
      return
    }

    logger.debug('%s (%s)', query.url, proxy)

    // handle grace time for preventing blocks or/and send the request
    if(GraceTime !== 0 && proxy.lastRequest && Date.now() < proxy.lastRequest.getTime() + GraceTime) {
      var wait = proxy.lastRequest.getTime() + GraceTime - Date.now()
      logger.debug('have to wait for %sms to prevent a block on proxy %s', wait, proxy.proxy)
      Proxies.waitTime+= wait
      setTimeout(function() {
        sendRequest(proxy, url, timeout, req, res)
      }, wait)
    } else {
      sendRequest(proxy, url, timeout, req, res)
    }
  })
}

proxy = Proxies.nextProxy(url.host, function(err, proxy) {
    if(err) {
      if(err === 'ALL_BLOCKED') {
        res.status(503).end('all proxies are blocked')
      } else {
        res.status(503).end('all proxies are broken')
      }
      return
    }

    logger.debug('%s (%s)', query.url, proxy)

    // handle grace time for preventing blocks or/and send the request
    if(GraceTime !== 0 && proxy.lastRequest && Date.now() < proxy.lastRequest.getTime() + GraceTime) {
      var wait = proxy.lastRequest.getTime() + GraceTime - Date.now()
      logger.debug('have to wait for %sms to prevent a block on proxy %s', wait, proxy.proxy)
      Proxies.waitTime+= wait
      setTimeout(function() {
        sendRequest(proxy, url, timeout, req, res)
      }, wait)
    } else {
      sendRequest(proxy, url, timeout, req, res)
    }
  })
}

ProxyManager.nextProxy = function(host, cb) {
  if(this.allBroken()) {
    if(this.allBlocked()) {
      this._allBlocked = true
      return cb('ALL_BLOCKED')
    }
    return cb('ALL_BROKEN')
  }
  // increment the index value for the host
  if(typeof Index[host] === 'undefined' || list.length === Index[host] + 1) {
    if(typeof Index[host] === 'undefined') {
      logger.debug('all proxies used, starting new cycle')
    }
    Index[host] = 0
  } else {
    Index[host]++
  }
  var proxy = list[Index[host]]

  if(proxy.errors >= MaxErrors && proxy.hits === 0) {
    // if a proxy 
    return this.nextProxy(host, cb)
  } else if(!AllowMultipleCalls && proxy.inUse) {
    // once we hit a proxy in use, we check if any other is free at the moment, 
    // if not, we sleep for a small amount of time
    if(!AllowMultipleCalls && this.allInUse()) {
      var that = this
      this.timeWaited+= UseWaitTime