app.js

Ext.require('Ext.container.Viewport');

Ext.application({
    name:'HelloExt',
    launch: function(){
        Ext.create('Ext.container.Viewport', {
            layout: 'fit', 
            items: [
                {
                title: 'Hello Ext', 
                html:  'Hello!'
            }
            ]
        });
    }
})