Ext.Loader.setConfig({enabled:true});

Ext.application({
    name: 'app',
    controllers:[
  ],
    appFolder: 'app',
    launch: function() {
        var panel = new Ext.form.FormPanel({
          renderTo:Ext.getBody(),
          title:'Panel',
          width:400,
          bodyPadding: 10,
          autoHeight:true,
          items:[{
            xtype:'textareafield',
            name: 'textInput',
            id:'textId',
            value:'why not'
          },{
            xtype:'button',
            text:'Helllo',
            handler:function(){
              console.log('button click')
              var tf = Ext.get('textId');
                    tf.setValue('This should change!')
            }
          }],
        });
    }
});