ExtJs4 : Dynamically Add Columns

Cod Snippet for Dynamically Adding Columns to a grid panel in Extjs4

Ext.create('Ext.data.Store', {
    storeId:'simpsonsStore',
    fields:['name', 'email', 'phone'],
    data:{'items':[
        { 'name': 'Lisa',  "email":"lisa@simpsons.com",  "phone":"555-111-1224"  },
        { 'name': 'Bart',  "email":"bart@simpsons.com",  "phone":"555-222-1234" },
        { 'name': 'Homer', "email":"home@simpsons.com",  "phone":"555-222-1244"  },
        { 'name': 'Marge', "email":"marge@simpsons.com", "phone":"555-222-1254"  }
    ]},
    proxy: {
        type: 'memory',
        reader: {
            type: 'json',
            root: 'items'
        }
    }
});

Ext.create('Ext.grid.Panel', {
    id: 'gridpanel',
    title: 'Simpsons',
    store: Ext.data.StoreManager.lookup('simpsonsStore'),
    columns: [
        { header: 'Name',  dataIndex: 'name' },
        { header: 'Email', dataIndex: 'email', flex: 1 },
        { header: 'Phone', dataIndex: 'phone' }
    ],
    height: 200,
    width: 600,
    renderTo: Ext.getBody(),
        dockedItems: [{
            xtype: 'toolbar',
            items: [
                {
                text: 'add column',
                handler: function(){
                    var gridView = Ext.ComponentQuery.query("gridpanel")[0];
                    var column = Ext.create('Ext.grid.column.Column', {text: 'New Column'});
                    gridView.headerCt.insert(gridView.columns.length, column);
                    gridView.getView().refresh();
                }}

            ]
        }]
});