ExtJS 4自动解析元数据

Ok, in my application, I have extra information sent with the data, which the Sencha docs define as metadata. If there was an error retrieving data, say for a grid, i want the server to be able to tell the client to inform the user that it was unable to complete the request. But I want to do this for EVERYTHING, and not have to redefine a callback to check on every store in my application. Is there a way to do this? Or am I trying to do this all wrong? Also, how can I go about utilizing the JSON Reader without using stores or models? That way I can do the same thing, intrepting server instructions, without having to redefine it in an Ext.Ajax success callback?

For a store, you can

Ext.define('myNewCustomStore',{
    constructor:function(config){
        this.callParent(arguments);
        this.on('load',function(store,records,e){myCustomMetaDataHandler()});
    }
});

And then instead of using

Ext.create('Ext.data.Store' or Ext.define('myStore',{extends:Ext.data.Store You create / extend myNewCustomStore

And Json without models?

Ext.Ajax.request({
url: 'page.php',
params: {
    id: 1
},
success: function(response){
    var text = response.responseText;
    var json = Ext.JSON.decode(text);
    //now do stuff
}
});