extjs4 why does not the api property work in Store - extjs4.1

Question

I'm trying to take a test api property of ajax proxy in store, but seems it does not work.
I have no idea why it does not work. I've just followed reference book.
Would someone please give me an advice ? I've attached source code.
Below is source code for model.
Ext.define('directModel', {
extend : 'Ext.data.Model',
fields : [
{name : 'id', type : 'int'},
{name : 'firstName', type : 'string'},
{name : 'lastName', type : 'string'},
{name : 'company', type : 'string'},
{name : 'email', type : 'string'},
{name : 'dob', type : 'date'},
{name : 'age', type : 'int'},
{name : 'coworker', type : 'string'}
]
});
Below is source code for store.
var store = Ext.create('Ext.data.Store', {
storeId : 'directStore',
model : 'directModel',
proxy : {
type : 'ajax',
api : {
read : '/common/command.jsp?action=read',
create : '/common/command.jsp?action=add',
update : '/common/command.jsp?action=update',
destory : '/common/command.jsp?action=remove'
},
reader : {
type : 'json',
root : 'root'
},
writer : {
type : 'json',
root : 'data'
}
}
});
var s = Ext.data.StoreManager.get('directStore');
s.load({
callback : function(){
var r = Ext.ModelManager.create({
id : '346012',
firstName : '',
lastName : '',
company : '',
email : '',
dob : '',
age : 3,
coworker : 'N/A'
}, 'directModel');
s.add(r);
s.sync();
}
});
I just loaded store to bring the data from server side and I found out it's okay.
Also I tried to add new reocrd and invoke "sync" function.
As I know, request url should be create property of api. However nothing happened.
pls give me an advice.