nodejs pass server instance to a class as a property

I have a question about passing an instance, as following

app.js

// nodejs var
var app = express()
    , server = http.createServer(app)
    , _Server = io.listen(server);


/**
 * To log
 * Before, to display the _Server instance, the content should be
 */
console.log(util.inspect(_Server));


// app var
var _Session = new Session(_Server);

session.js

var Session = function Session(server) {
    this.m_server = server;

    /**
     * To log
     * After, to display the m_server property, the content actually is
     */
    console.log(util.inspect(this.m_server));
}

I wonder why those results aren't the same as I expect. And as a result I couldn't call this.m_server.emit(...) in the Session class. What I want to do is to delegate a behavior

from
    _Server.emit(...) // in app.js
to
    this.m_server.emit(...) // in session.js

So that lots of events could be implemented in different files. How can I do to make it ? thanks~