CODEWITHSUNDEEP
objectknockout.js
Math chiller
Math chiller

Reputation: 4167

using object.defineproperty with knockout observables

can i (and if yes how) create a ko.observable out of a object.defineproperty something like this

Strength: ko.observable(
    Object.defineProperty(this, "strength", {
        get: function () {
            return this.level * 2;
        },
        enumerable: true
    });
)

and 

<span> str: <span data-bind="text: Strength"></span> / 100 </span>

what im trying to do is update the display of strength when its called after every level-up

i.e.

  1. level up
  2. (fight) request the current strength
  3. update strength (+=2)
  4. update strength display

using Object.defineProperty

i would probably just use ko.computable, but im wondering if there is a way to do it.

Upvotes: 0

Views: 1148

Answers (2)

EricP
EricP

Reputation: 3439

The Knockout ES5 plugin will do what you need. Although I had to also include the Weakmap shim to make it work.

Upvotes: 1

Jaak K&#252;tt
Jaak K&#252;tt

Reputation: 2656

a bit unclear what you want to achive but I'd go with ko.computed. If you want the subscribers (namely your span) of your Strength property to be notified (when the level changes after the initial binding), you should also make level observable.

if you still want to use defineProperty, I hope this little example suits you (edit: added a button to level up)

function ViewModel() {
    var self = this;
    self.level=ko.observable(5);
    self.really_use_computed = ko.computed(function() {
        return self.level() * 2;
    });
}

var MyViewModel=new ViewModel();

Object.defineProperty(MyViewModel, "Strength", {
    get: function () {
        return this.level() * 2;
    },
    enumerable: true
});

ko.applyBindings(MyViewModel);

please note that Internet Explorer 8 standards mode supports DOM objects but not user-defined objects for the first argument of Object.defineProperty() and that earlier versions of IE don't support Object.defineProperty() at all.

Upvotes: 2

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