Backbone Models: defaults based on a condition

Question

I'm pretty new to BackboneJS, looking for some help in the defaulting an attribute based on a condition How can I default name to TEST based on a condition that is only if model.attribute = 'xyz' in Backbone models.

defaults: function() {
  return {
   name: 'TEST'
  }
}

Thanks

vassiliskrikonis · Accepted Answer · 2017-07-12 06:50:00Z

2

You set defaults when you extend a Backbone model so you don't really have access to any instance attributes there.

If the default values you want to change depend on instance modal attributes set on instatiation (i.e new MyModel({foo:"bar"})) when you'd be better of setting an initialize() callback when extending your model.

var MyModel = Backbone.Model.extend({
  initialize: function(options) {
    // I have access to this.attributes here
  }
});

answered Jul 12, 2017 at 6:50

vassiliskrikonis

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5 Comments

Emile Bergeron Over a year ago

Notice that defaults is a function in the question. So your first sentence is wrong. this.attributes is empty when accessed in the defaults function because attributes are in the process of being set, hence the defaults function being called.

InquisitiveGirl Over a year ago

That makes sense, Thanks all for your help.

vassiliskrikonis Over a year ago

@EmileBergeron I think there's nothing wrong with what I've said. Instance attributes haven't been populated at the time the defaults is evaled through Underscore's result()

Emile Bergeron Over a year ago

"when you extend a Backbone model", written as if the code runs only when extending the model class, which is false since it's a function that is called each time a model is instantiated. You do have access to the instance attributes hash, but it is empty at that point. What you don't have access to is the passed attributes (new MyModel({foo:"bar"})) because the defaults function receives no parameters.

Emile Bergeron Over a year ago

I did upvote you though, that is just nitpicking on my part ;)

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