async database connection manager, singleton pattern

db_con.js

var path= require('path');
//var cpath= path.resolve(__dirname, '..', '..', '..', 'node_modules', 'cassandra-client');
var Connection = require('cassandra-client').Connection;
var EventEmitter = require('events').EventEmitter;


/*
* four stages of connection
* 1. restart the server, connection is null
* 2. new Connection(options), but not yet connect, (client= null, doesn't have con, nothing in validators)
*************************
{ validators: {},
  client: null,
  connectionInfo: { host: '127.0.0.1', port: 9160, keyspace: 'clubond_1_1' },
  timeout: 4000,
  query_timeout: 5000,
  cql_version: undefined,
  _id: 1,
  _pendingQueryCallbacks: {},
  _queryIdCounter: 0,
  domain: 
   { domain: null,
     _events: { error: [Function] },
     _maxListeners: 10,
     members: [ [Object], [Object] ] },
  _events: null,
  _maxListeners: 10 }
**************************
*
* connect will add `con` and `client`
* 3. connnect not yet callback, still connecting!!!!,  connection.con.connected is false
* 4. connected after login learn use, connection.con.connected is true
* 
* 
*/


var connection = null;
//first stage- connection is null

var conManager= new EventEmitter();


module.exports = function (_options, callback){
    var options = _options;
    if(connection && typeof connection.con !== 'undefined' && connection.con.connected)
      return callback(null, connection);

    //stage 2- wait for connection
    if(connection && typeof connection.con !== 'undefined' && !connection.con.connected){
      conManager.on('connected', function (con) {
        callback(null, con);
      })

      conManager.on('error', function (err) {
        callback(err);
      })

      return;
    }

    //stage 1- connection is null- create a conneciton
    if(!connection){
      conManager.on('connected', function (con) {
        callback(null, connection);
      })

      conManager.on('error', function (err) {
        callback(err);
      })

      connection= new Connection(options);
      connection.connect(function(err) {
        if (err) 
          return conManager.emit('error', err);

          return conManager.emit('connected', connection);
      });
    }

};