A simple plugin that brings async sugar to any component that uses a card layout

gistfile1.js

/**
 * This plugin brings missing async features to card layouts. It can be applied
 * on any component that uses a card layout (e.g. a NavigationView)
 *
 * With this plugin you can do the following:
 *
 * navigationView.setActiveItem(fooCard, function(){ alert('after transition'); });
 * navigationView.push(fooCard, function(){ alert('after transition'); });
 * navigationView.pop(function(){ alert('after transition'); });
 *
 * You can also listen for the event 'activeitemchangecompleted' now.
 */
Ext.define('CouchCommerce.plugins.CardLayoutEvents', {

    extend: 'Ext.Component',

    alias : 'plugins.cardlayoutevents',

    init: function(parent) {

        var me = this;

        [
            'setActiveItem',
            'push',
            'pop'
        ].forEach(function(item){
            me._augmentWithCallback(parent, item);
        });
    },

    _augmentWithCallback: function(parent, functionName){
        var original = parent[functionName];

        if (!original){
            //we also asyncify methods that are only available on the
            //NavigationView (push, pop). This plugin is meant to be used
            //on other container derived components that might lack those,
            //hence the safety check here.
            return;
        }

        parent[functionName] = function(){

            var lastParameter = arguments[arguments.length - 1];
            var isCallback = Ext.isFunction(lastParameter);

            if (isCallback){
                parent.on('activeitemchange', lastParameter, parent, {
                    single: true
                });
            }

            //be aware that we call the original method with our augmented
            //callback parameter. So we assume the parameter is not used
            //anyway and there won't have side effects.
            original.apply(parent, arguments);
        }
    }
});

It currently has bugs though. The handler fires two times when it shouldn't. I'll need to investigate that further.

Btw, if sencha had first class promises/deferred support those three methods should actually return a deferred object instead of accepting a callback. I hope someone at sencha hears me ;-)

Oh, I'm missing checks for the push and pull part because those only exist on the navigation view but the plugin can be applied to any component that uses a card layout.

I added the safety checks for push and pop