Extending a class other than ExtJS (like OpenLayers.Map)

[JoepRonde]

In ExtJS 3.2  I extended a class which is not part of the ExtJS framework (the OpenLayer.Map class) with the folowing code:

MyMap = Ext.extend(OpenLayers.Map, {
    constructor: function() {
        config = {
            div: 'olMap',
            projection: 'EPSG:28992'
            // ... other config settings
        }
        MyMap.superclass.constructor.call(this, config)
    },

    myFunction: function() {
        //Do something
    }
});

This all worked fine, the constructor above created a OpenLayer.Map instance and returned it. But now I'm upgrading to ExtJS 4 and would like to do exactly the same, but I can't make it work. The code I have so far is this:

Ext.define('MyMap', {
    extend: 'OpenLayers.Map',
    constructor: function() {
        config = {
            div: 'olMap',
            projection: 'EPSG:28992'
            // ... other config settings
        }
        this.callParent(arguments);
        this.initConfig(config);
    },

    myFunction: function() {
        //Do something
    }
});

The constructor above doesn't create return an instance of OpenLayers.Map though. I thought that this.callParent in the constructor should create a instance it's parent class (OpenLayer.Map), but is does not. So now I am wondering how can I extend a class other than an ExtJS class?

[scottmartin]

Move to Q&A, plugins is for release.

Scott.