Ext.onReady(function(){

    Ext.create('Ext.panel.Panel', {

        id: 'myPanel',

        title: 'Ext Panel',

        renderTo: Ext.getBody(),

        width: 300,

        height: 200,

        dockedItems: [

            {

                xtype: 'toolbar',

                dock: 'top',

                items: [

                    {

                        text: 'click me',

                        handler: function(){

                            Ext.getCmp('myPanel').setTitle('Change Panel Title');

                        }

                    }

                ]

            }

        ]

    });

});