How to pass scope to callback functions in nodejs?

Im using nodejs and the xml2js module. I'm reading an XML file and try to emit an event after the xml is converted to an json object. My code looks like this :

var fs = require('fs'),
util = require('util'),
events = require('events'),
xml2js = require('xml2js');

var CIRCUITMODELSFILENAME = "ControlCircuitModels.xml";
var CIRCUITPARTMODELSFILENAME = "ControlCircuitParts.xml";
var circuitModels, circuitPartModels;


function ModelController() {
    if (false === (this instanceof ModelController)) {
        return new ModelController();
    }
    events.EventEmitter.call(this);
};


util.inherits(ModelController, events.EventEmitter);


ModelController.prototype.load = function (baseDir) {

    var parser = new xml2js.Parser({
        normalize: true,
        trim: true,
        explicitArray: false
    });

    fs.readFile(baseDir + "/" + CIRCUITMODELSFILENAME, function (err, data) {
        parser.parseString(data, function (err, result) {
            circuitModels = result;
            console.log('circuit models loaded');
            parser.reset();
            fs.readFile(baseDir + "/" + CIRCUITPARTMODELSFILENAME, function (err, data) {
            parser.parseString(data, function (err, result) {
                circuitPartModels = result;
                console.log('circuit part models loaded');
                moduleReady = true;
                this.emit("modelsloaded", null);
                });
            });
        });
    });
};

// public interface
exports.ModelController = ModelController;

Problem is that the scope when emitting the event is lost.

this.emit("modelsloaded", null);

this hasn't inherited the emit from EventEmitter.

How can I pass the scope to the parser.parseString function?

Thanks Chris