Just started `Backbone.js` and following tuorials at backbonejs.org. 

Here is what I wanted to achieve. I created a model which asks for width and saves it. Now I have used `listenTo` with `object` I have created as below on `model` to read the changed property value. It triggered the `change` `event`, but, I always get `undefined` for width. Code is below.

```
var mod = Backbone.Model.extend({
    askColor:function() {
        var w = prompt("Enter width");
        this.set({ width:w})
    }
});

var model = new mod();
model.set({width:1234})

var obj = {};
_.extend(obj,Backbone.Events);
obj.listenTo(model, 'change', function() {
    alert("width = "+model.width)
})
model.askColor();

```

I really don't know what am I missing in the code or am I doing wrong? Please help out a beginner....