Backbone.js model.get() not work - backbone.js

Question

In below code, when i want to use get() method as seen in code return undefined. what's the problem.
<script type="text/javascript">
(function() {
window.App = {
Models: {},
Views: {}
};
window.vent = _.extend({}, Backbone.Events);
})();
//Model
App.Models.User = Backbone.Model.extend({
url: '/users'
});
var user = new App.Models.User();
user.fetch({
success: function (user) {
console.log(user.get('firstname'));
}
});
</script>

Answer 1

That's because the value given to the success callback isn't a Backbone model, it's jsut the raw server responsse. To display the first name as soon as the data is fetched, you can use a deferred (see http://api.jquery.com/jQuery.Deferred/):
var user = new App.Models.User();
$.when(user.fetch()).done(function(){
console.log(user.get("firstname");
});

Answer 2

Your Example is working for me here it is http://jsfiddle.net/YYM43/
Try to see if you have loaded the libs (Backbone.js ...) correctly.
(function() {
window.App = {
Models: {},
Views: {}
};
window.vent = _.extend({}, Backbone.Events);
})();
//Model
App.Models.User = Backbone.Model.extend({
url: 'http://echo.jsontest.com/name/betty/age/22'
});
var user = new App.Models.User();
user.fetch({
success: function (user) {
console.log(user.get('age'));
}
});