title: How do I add a listener that will work on individual Fieldset in Extjs? Clicking the "Add" button shows the error
body: <pre><code>&lt;html&gt;
  &lt;head&gt;
  &lt;title&gt;Testing Window&lt;/title&gt;
  
  &lt;script type="text/javascript" src="http://www.extjs.com/deploy/ext-3.1.1-rc/adapter/ext/ext-base.js"&gt;&lt;/script&gt;
  &lt;script type="text/javascript" src="http://www.extjs.com/deploy/ext-3.1.1-rc/ext-all-debug.js"&gt;&lt;/script&gt;
  &lt;link rel="stylesheet" type="text/css" href="http://www.extjs.com/deploy/ext-3.1.1-rc/resources/css/ext-all.css" /&gt;
  
  &lt;/head&gt;
  
  &lt;!-- Revised from demo code in ext3.0.0 --&gt;
  &lt;body&gt;
  &lt;script type="text/javascript"&gt;
  /*!
   * Ext JS Library 3.0.0
   * Copyright(c) 2006-2009 Ext JS, LLC
   * licensing@extjs.com
   * http://www.extjs.com/license
   */
  Ext.onReady(function(){
  
      Ext.override( Ext.data.Store, {
          findExact: function( fld, val ) {
              var hit = null;
              this.each( function(rec) { if( rec.get(fld) == val ) { hit = rec; return false; }; } );
              return hit;
          }
      });
  
      var listAdded = 0;
  
      var addListBtn = {
          text: 'Add',
          handler: function() {
              Ext.getCmp('tab_list').add(getList());
              Ext.getCmp('tab_list').doLayout();  
          }
      }
  
      var testData = new Ext.data.SimpleStore({
      fields: ['no', 'name', 'address','phone','businessPhone'],
      data: [['68', 'Target','123 Valley Road','(345) 908-9087','(345) 908-9087'], 
             ['69', 'Walmart','456 Main Road','(345) 908-9999','(345) 908-9990']]
      }); 
  
  
      var getList = function() {
          listAdded++;
  
          var items = new Ext.form.FieldSet(
          {
          id:listAdded,
          title: listAdded,
          collapsible: true,
          layout: 'form',
          autoHeight: true,
          defaults: {width: 300},
          defaultType: 'textfield',
          bodyStyle: 'padding:5px',
          labelWidth: 225,                
          items: [
              {
                  xtype: 'combo',
                  fieldLabel: 'Customer No',
                  name: 'changescustomerNo',
                  hiddenName: 'changescustomerNo',                        
                  store: new Ext.data.SimpleStore({
                      fields: ['id','value'],
                      data: [['68','Test1'],['69','Test2']]
                  }),
  
                  displayField: 'value',
                  valueField: 'id',
                  selectOnFocus: true,
                  mode: 'local',
                  editable: false,
                  triggerAction: 'all',
                  value: ' ',
                  listeners:{select:{ fn:function(combo, value) {
                      var m = testData.findExact( 'no', this.value );
                      if(m) {
                          //alert(this.id);
                          Ext.getCmp('currentName').setValue(m.get('name'));
                          Ext.getCmp('currentAddress').setValue(m.get('address'));
                          Ext.getCmp('currentTelephoneNumber').setValue(m.get('phone'));
                          Ext.getCmp('currentBusTelephoneNumber').setValue(m.get('businessPhone'));
                      }
                     }//function
                    }//select
                  }//listeners                        
              },{
                  id: 'currentName',
                  fieldLabel: 'Current Name',
                  name: 'currentName',
                  value: ''
              },{
                  id: 'currentAddress',
                  width: 298,
                  xtype: 'textarea',
                  fieldLabel: 'Current Address',
                  name: 'currentAddress',
                  value: ''
              },{
                  id:'currentTelephoneNumber',
                  fieldLabel: 'Current Telephone Number',
                  name: 'currentTelephoneNumber',
                  value: ''
  
              },{
                  id: 'currentBusTelephoneNumber',
                  fieldLabel: 'Current Business Telephone Number',
                  name: 'currentBusTelephoneNumber',
                  value: ''
              }
              ]
          }
          );      
          return items;
      }
  
      var pnlMain = new Ext.Panel({
          id: 'theForm',
          title: 'Sample List',
          bodyStyle:'padding:5px',
          autoWidth: true,
          frame: true,
          items: [{
              xtype: 'tabpanel',
              id: 'tabpanel',
              activeTab: 0,
              height: 540,
              width: '100%',
              resizeTabs: true,           
              tabWidth: 125,
              minTabWidth: 125,
              layoutOnTabChange: true,
              deferredRender: false, // Create all form elements on load
              defaults: {
                  bodyStyle: 'padding:10px', 
                  autoScroll: true, 
                  layout: 'form',
                  defaultType: 'textfield',
                  labelWidth: 160
              },
              items:[{
                  id: 'tab_list',
                  title: 'List',
                  items: getList(),
                  buttons: [
                      addListBtn
                  ]
              }]
          }]
      });
  
      pnlMain.render('main');
  });
  &lt;/script&gt; 
  
  
  &lt;div id="main"&gt;&lt;/div&gt;
  &lt;/body&gt;
  &lt;/html&gt;
  </code></pre>