TypeError javascript variable is undefined - ruby-on-rails

Question

in my ror app（ruby on rails），one of page google.js.erb function show google map， i add add position function，i use extjs frame，however i encounter some stronger problem， relative code is below
Ext.onReady(function () {
var mapOptions =
{
zoom: 6,
center: new google.maps.LatLng(30.26, 120.19),
mapTypeId: google.maps.MapTypeId.ROADMAP,
scaleControl: true,
mapTypeControl: true
};
var map = new google.maps.Map(Ext.getDom('mapDiv'), mapOptions);
var googlemappanel=Ext.create('Ext.panel.Panel', {
items: [
{
xtype: 'panel',
region: 'east',
items: [
Ext.create('Ext.form.Panel', {
id: 'zone-form',
items: [
{xtype:"textfield",fieldLabel: '<%= t('code') %>',name: "code", id: 'zoneid'}
],
buttons: [{
handler: function(){
Ext.getCmp('zone-form').getForm().submit({
url : 'basestation_edit',
success : function(form, action){
var base=action.result.griddata
for(var i=0; i<action.result.griddata.length; i++){
marker = new google.maps.Marker({
position: new google.maps.LatLng(base[i].latitude,base[i].longitude),
map: map
});
google.maps.event.addListener(marker, "click", function(event) {
Ext.getCmp('zoneid').setValue(base[i].id);
})
}
}
....
when i submit the form,google marker is added to the map. however when i click the marker, firebug throw out TypeError: base[i] is undefined error, google marker is added normal, it seems variable i is recovery，set global i don't solve the problem。
any help！