how to get Object param of (tab listeners: activate)?

Dear：

activate have 2 paramthis, object),

if if add an objY:{aa:"001",bb:"002"} for tab item,

and pass as activate: function(tab,objY){}

how can I get objY.aa in the function.

I have tried as: objY.aa or objY['aa']

but it is not work.

I have problem in ext to get josn object.

thx

Code:

  var tabs2 = Ext.create('Ext.tab.Panel',{  
        renderTo: document.body,  
                activeTab: 0,  
        width: 600,  
        height: 250,  
        plain: true,  
        margin:'0 10 0 80',  
        defaults :{  
              autoScroll: true,  
              bodyPadding: 10  
        },  
        items: [{   
                  title: '點觸發事件',  
                  listeners: {  
                      activate: function(tab,objY){  
                          alert(tab.title+objY);  
                      }  
                  },  
                  html: "XXXX",
                                    objY:{aa:"001",bb:"002"}  
              },{  
                  title: 'Tabs DISABLE',  
                  disabled: true  
              }  
        ]  
    })