When extending a backbone model or view, how can i create properties that get created on the instance and not on the prototype?

Question

I want to do:

var MyModel = Backbone.model.extend({
  someProp: { ... },
  .
  .
  });

but have new MyModel().someProp === new MyModel().someProp return false

as if i had done

function MyModel() {
 this.someProp = {...};
}

I dont want to put the assignment this.someProp = {...}; in the initialize method because if i subclass MyModel, i ll have to repeat the assignment also in the subclass's initialize method again or remember to call the parents initialize from the children initialize every time i subclass, which it seems to me as a workaround rather than a solution. So, is there any other way?

Answer 1

If you want to use it for multiple models, then one solution would be to create a standalone function that takes care of it, then you can call that function from the model's initialize method.

Here's an example

function addInstanceProperties() {
  this.someProp = 'hello';
  this.otherProp = 'world';
}

var Parent = Backbone.Model.extend({
  initialize: function() {
    //have to use 'call' so the context is set to this model
    addInstanceProperties.call(this); 
  }
});

var Child = Parent.extend({
  initialize: function() {
    addInstanceProperties.call(this);
  }
});

However, this isn't any different than having the property assignments in the parent and having the child call the parent's initialize method. And there is less code involved.

var Parent = Backbone.Model.extend({
  initialize: function() {
    this.someProp = 'hello';
    this.otherProp = 'world';
  }
});

var Child = Parent.extend({
  initialize: function() {
    Parent.prototype.initialize.call(this);
  }
});

Unless you want to repeat the property assignments in each initialize method, this is really the only other way to do it in Javascript.