CODEWITHSUNDEEP
javascriptbackbone.js
homtg
homtg

Reputation: 1999

defineProperty on Backbone model

If i want to add a custom property to my backbone model, is this the best was to do this? Is there a better way or a completely different approach to the functionality i want to achieve?

var myModel = Backbone.Model.extend({

   defaults:{
    monthly_amount: 100
   },

   initialize: function(model, options){

     var m = this;

     Object.defineProperty(this,"yearly_amount",{
       get: function() {
                         return (m.get("monthly_amount") * 12);
                       },
       set: function(value) {
                         m.set("monthly_amount", (value/12) );
                       }
     });

   }
});

Thanks!

Edit: The property is just "virtual", i do not want it to be within the model attributes when saving the model to the server.

Upvotes: 7

Views: 541

Answers (2)

Vitalii Del Vorobioff
Vitalii Del Vorobioff

Reputation: 524

When you set your property to defaults oject, it goes to attributes, but it doesn't suit us. Since Backbone model is an regular object, you can access to it's properties as to objects properties:

var myModel = Backbone.Model.extend({}),
    model = new myModel();

model.monthly_amount = 50;
console.log(model.monthly_amount)

or create setter and getter like this:

var myModel = Backbone.Model.extend({
    setMonthlyAmount: function (value) {
        this.monthly_amount = value;
    },

    getMonthlyAmount: function () {
        return this.monthly_amount;
    }

});

//access with getter/setter
var model = new myModel();

model.setMonthlyAmount(20);
var result = model.getMonthlyAmount();
console.log(result);

Working example on jsfiddle

Upvotes: 0

Peter Lyons
Peter Lyons

Reputation: 146084

So the general problem here is often referred to as "computed properties" and there are plugins for backbone that provide this (see below). Backbone uses get/set method calling style as opposed to defineProperty style so your approach would make the value computation not transparent to views and thus be a pretty strong departure from backbone's design. A plugin that maintains the proper get/set and change interfaces is going to maintain the basic Model API so the view doesn't have to treat this particular model attribute differently.

See also the backbone wiki of plugins.

Available plugins:

Upvotes: 2

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