Initialization of hasListeners object on class prototypes

gistfile1.js

    Ext.define('Observable', {
        hasListeners: {},
        observableType: 'observable',

        onClassMixedIn: function(Class) {
            var prototype = Class.prototype;

            if (prototype.hasOwnProperty('observableType')) {
                prototype.hasListeners = {};
            }

            Class.onExtended(function(Class, data) {
                if (data.observableType) {
                    data.hasListeners = {};
                }
            });
        },

        onClassExtended: function(Class, data) {
            if (data.observableType) {
                data.hasListeners = {};
            }
        }
    });
    

    Ext.define('Component', {
        mixins: ['Observable'],
        observableType: 'component'
    });

    Ext.define('Button', {
        extend: 'Component'
    });

    Ext.define('SplitButton', {
        extend: 'Button',
        observableType: 'splitbutton'
    });

    console.log(Component.prototype.hasOwnProperty('hasListeners')); // true
    console.log(Button.prototype.hasOwnProperty('hasListeners')); // false
    console.log(SplitButton.prototype.hasOwnProperty('hasListeners')); // true

    Ext.define('Foo', {
        extend: 'Observable',
        observableType: 'foo'
    });

    Ext.define('Bar', {
        extend: 'Foo'
    });

    Ext.define('Baz', {
        extend: 'Bar',
        observableType: 'baz'
    });

    console.log(Foo.prototype.hasOwnProperty('hasListeners')); // true
    console.log(Bar.prototype.hasOwnProperty('hasListeners')); // false
    console.log(Baz.prototype.hasOwnProperty('hasListeners')); // true