Default (complex) attributes are by reference for multiple instances of a model.

[slikrik98]

If you have an object specified as a 'default' attribute in your model, all instances of this model will share a reference to that object. Is there a reason we don't do a deep clone on the defaults object when creating a new Model instance?

As it is currently, if you make changes to a deep attribute of that object, you will be updating all model instances. Is this by design?

[jridgewell]

That's a common gotcha in all JavasScript, not just Backbone. You're better off using a function that returns your defaults instead.

var Model = Backbone.Model.extend({
  defaults: function() {
    return {
      deep: { object: true }
    };
  }
});

[slikrik98]

Does Backbone discourage the use of objects for model attributes?

[Florian-R]

Yap, see #3457