title: Cannot read property 'connect' of undefined
body: <p>I'm writing a nodejs application.</p>
  
  <p>I'm trying to use the async plugin to connect, query and disconnect from db.</p>
  
  <p>the 'class' that I created is the following:</p>
  
  <pre><code>var config = ini.parse(fs.readFileSync('config/config.ini', 'utf-8'));
  var mysql = require('mysql');
  
  var inspect = require('util').inspect;
  module.exports = TuxDb;
  
  function TuxDb() {
      this._connection = mysql.createConnection({
      host: config.db.host,
      user: config.db.username,
      password: config.db.password,
      database: config.db.schema
  });
  }
  
  TuxDb.prototype.connect = function (callback) {
   this._connection.connect(function (err) {
      callback(err, null);
   });
  }
  </code></pre>
  
  <p>and the code:</p>
  
  <pre><code>var TuxDb = require('../../db/db.js');
  var tuxDB = new TuxDb();
    async.series([tuxDB.connect,
      function (callback) {
          tuxDB.getGenericDrinks(callback);
      }, function (callback) {
          tuxDB.disconnect(null, callback);
      }
  ], function (err, result) {
      if (err != null) {
          return next(new restify.InvalidArgumentErrror(err));
      }
  });
  </code></pre>
  
  <p>i get the following error:</p>
  
  <pre><code>TypeError: Cannot read property 'connect' of undefined
  </code></pre>
  
  <p>I don't quite understand why. the constructor already sets <code>this._connection</code> so why in the connect function <code>this._connection</code> is null?</p>