serverSend.js

/**
 * @description
 * Extend loglevel with new plugin which will send log information to the log-sever
 *
 * @param {object} logger loglevel instance to be extended
 * @param {object} options
 * @param {string} [options.url='http://localhost:8000/main/log'] Server url which would be used as a log server
 * @param {string|Function} [options.prefix=null] Prefix for all log messages. Either string or function wich should return string and accept log severity and message as parameters
 * @param {Bool} [options.callOriginal=false] If set to true - original loglevel method for logging would be called
 * @param {string} [options.websocket] Send data over websocket instead of ajax
 * @example
 * loglevelServerSend(log,{url:'https://example.com/app/log',prefix: function(logSev,message) {
 *     return '[' + new Date().toISOString() + '] ' + logSev + ': ' + message + '\n'
 * }})
 */
loglevelServerSend = function (logger, options) {
  if (!logger || !logger.methodFactory)
    throw new Error('loglevel instance has to be specified in order to be extended');

  var _logger = logger,
    _url = options && options.url || 'http://localhost:8000/main/log',
    _callOriginal = options && options.callOriginal || false,
    _prefix = options && options.prefix,
    _originalFactory = _logger.methodFactory,
    _sendQueue = [],
    _isSending = false;

  _logger.methodFactory = function (methodName, logLevel) {
    var rawMethod = _originalFactory(methodName, logLevel);

    return function (message) {
      if (typeof _prefix === 'string')
        message = _prefix + message;
      else if (typeof _prefix === 'function')
        message = _prefix(methodName, message);
      else
        message = methodName + ': ' + message;

      if (_callOriginal) {
        rawMethod(message);
      }

      _sendQueue.push(message);
      _sendNextMessage();
    }
  };

  _logger.setLevel(_logger.levels.INFO);

  var _sendNextMessage = function () {
    if (!_sendQueue.length || _isSending) {
      return;
    }

    _isSending = true;

    var msg = _sendQueue.shift();

    if (options.websocket) {
      options.websocket.send(msg);
      _isSending = false;
      setTimeout(_sendNextMessage, 0);
    }
    else {
      var req = new XMLHttpRequest();

      req.open("POST", _url, true);
      req.setRequestHeader('Content-Type', 'text/plain');
      req.onreadystatechange = function () {
        if (req.readyState == 4) {
          _isSending = false;
          setTimeout(_sendNextMessage, 0);
        }
      };

      req.send(msg);
    }
  }
};