observableArray filter prototype extend

observable-filter.js

ko.observableArray.fn.filterByProperty = function(propName, matchValue) {
    return ko.computed(function() {
        var allItems = this(), matchingItems = [];
        for (var i = 0; i < allItems.length; i++) {
            var current = allItems[i];
            if (ko.utils.unwrapObservable(current[propName]) === matchValue)
                matchingItems.push(current);
        }
        return matchingItems;
    }, this);
}