[extjs] Динамический grid

function Grid(urlHead, urlData){
    var grid = new Ext.grid.GridPanel({});

    Ext.Ajax.request({
        loadMask: true,
        url: urlHead,
        success: function(response, callOptions){
            var store = new Ext.data.JsonStore({
                url: urlData,
            });

            grid = new Ext.grid.GridPanel({
                store: store,
                columns: Ext.encode(response.responseText),

                height: 300,
                title: 'Basic GridView',
                iconCls: 'icon-grid',

                bbar: new Ext.PagingToolbar({
                    pageSize: 10,
                    store: store,
                    displayInfo: true,
                })
            });
        },
        failure: function(response, callOptions) {}
    });
    return grid;
}

[
    {header: "ID", width: 4, sortable: true, dataIndex: 'id'},
    {header: "Name", width: 50, sortable: true, dataIndex: 'last'}
]

{"success":true,"message":"Loaded data","data":[{"id":1,"first":"Fred","last":"Flintstone","email":"fred@flintstone.com"},{"id":2,"first":"Wilma","last":"Flintstone","email":"wilma@flintstone.com"},{"id":3,"first":"Pebbles","last":"Flintstone","email":"pebbles@flintstone.com"},{"id":4,"first":"Barney","last":"Rubble","email":"barney@rubble.com"},{"id":5,"first":"Betty","last":"Rubble","email":"betty@rubble.com"},{"id":6,"first":"BamBam","last":"Rubble","email":"bambam@rubble.com"}]}