Call view function from event handler?

How can I call a function from an event handler?

webix.protoUI({
    name:'customView',
    $init: function (config) {
        config.head = {
            view: 'toolbar',
            height: "auto",
            cols: [
                {
                    align: 'center', 
                },
                {
                    view: "button",
                    id: "New_" + _id,
                    value:"+New",
                    width:100,
                    on: {
                        onItemClick: function() {
                            this.addNew();  // does not work
                            $$(this.config.id).addNew();  // does not work
                        }
                    }
                },
                { 
                    view: 'button', 
                    align: 'right', 
                    type: 'icon', 
                    icon: 'close', 
                    width: 30, 
                    on: {
                        onItemClick: function () { webix.message("Close!"); }
                    },
                }
            ]
        };
        config.body = {
            
            view: 'scrollview',
            scroll: 'y',
            body: {  ... },
            width: 600,
            height: 400
        };
    },
    addNew: function () {
        // do cool stuff
    }
}, webix.ui.window);

Hi,

this that is in onItemClick event handler refers to button view. getTopParentView() method allows to get window:

...
 this.getTopParentView().addNew();
...

Thanks!