Knockout JS Conditioned Observable

knockout.conditioned-observable.js

"use strict";
ko.conditionedObservable = function (initialValue, condition) {
    var obi = ko.observable(initialValue);
    var computer = ko.computed({
        read: function () { return obi(); },
        write: function (newValue) {
            //unwrap value - just to be sure
            var v = ko.unwrap(newValue);
            //check condition
            if (condition(v)) {
                //set it to the observable
                obi(v);
            }
            else {
                //reset the value
                computer.notifySubscribers();
            }
        }
    });
    return computer;
};

The gist is part of Conditioning Knockout Observables: reject values blog.