Backbone.js is a JavaScript frameworks for creating MVC-like web applications.
Defining Model in Backbone.js
Models can be created by extending Backbone.Model
A model is basically a Javascript object, i.e. key-value pairs, with some helper functions to handle event triggering, persistence, etc.

P.S:The initialize() method is called when a new instance of a model is created.Similarly default is used to set the default values(Optional)
Getters & Setters
Model.get() provides easy access to a model’s attributes. Attributes which are passed
through to the model on instantiation are instantly available for retrieval.

If you want to get all atrributes in JSON use Model.toJSON() method.

Model.set() allows us to pass attributes into an instance of our model. Attributes can either be set during initialization or at any time afterwards.

Validation in Backbone.js Model
Backbone supports model validation through Model.validate().If doesn’t return anything when valid and return custom error when invalid.