Sencha Touch JSON-P and Ruby on Rails

SampleController.rb

class SampleController < ApplicationController
  respond_to :json

  def index
    @nodes = Node.all
    render :json => @nodes.to_json, :callback => params[:callback]
  end
end
                                                            

SampleStore.js

Ext.define('App.store.SampleStore', {
    extend: 'Ext.data.Store',
    requires: [
        "Ext.data.proxy.JsonP"
    ],

    config: {
        model: 'App.model.Sample',
        autoLoad: true,

        proxy: {
            type: 'jsonp',
            url: 'http://www.example.com/nodes.json',
            reader: {
                type: "json",
                rootProperty: ""
            }
        },
    }
});