Determine if an object property is ko.observable

I'm using KnockoutJS version 2.0.0

If I'm looping through all properties of an object, how can I test whether each property is a ko.observable? Here's what I've tried so far:

    var vm = {
        prop: ko.observable(''),
        arr: ko.observableArray([]),
        func: ko.computed(function(){
            return this.prop + " computed";
        }, vm)
    };

    for (var key in vm) {
        console.log(key, 
            vm[key].constructor === ko.observable, 
            vm[key] instanceof ko.observable);
    }

But so far everything is false.

Knockout includes a function called ko.isObservable(). You can call it like ko.isObservable(vm[key]).

Update from comment:

Here is a function to determine if something is a computed observable:

ko.isComputed = function (instance) {
    if ((instance === null) || (instance === undefined) || (instance.__ko_proto__ === undefined)) return false;
    if (instance.__ko_proto__ === ko.dependentObservable) return true;
    return ko.isComputed(instance.__ko_proto__); // Walk the prototype chain
};

UPDATE: If you are using KO 2.1+ - then you can use ko.isComputed directly.

Knockout has the following function which I think is what you are looking for:

ko.isObservable(vm[key])

To tack on to RP Niemeyer's answer, if you're simply looking to determine if something is "subscribable" (which is most often the case). Then ko.isSubscribable is also available.

I'm using

ko.utils.unwrapObservable(vm.key)

Update: As of version 2.3.0, ko.unwrap was added as substitute for ko.utils.unwrapObservable