Ext.onReady(function(){
    
    Ext.getBody().update();
    new Ext.TabPanel({
        autoHeight: true,
        title: 'tabPanel',
        width:300,
        activeTab: 0,
        renderTo: Ext.getBody(),
        items: [{
            title: 'FormPanel',
            xtype: 'form',
            autoHeight: true,
            buttons: [{text:'adf'}], // Try comment this line
            bodyStyle: 'padding:10px',
            defaultType: 'textfield',
            items: [{
                fieldLabel: 'Label 1'
            },{
                fieldLabel: 'Label 2'
            },{
                fieldLabel: 'Label 3'
            },{
                fieldLabel: 'Label 4'
            }]
        }]
    });
    
});