ko has items

ko.observableArray.fn.trackHasItems = function () {
        //create a sub-observable
        this.hasItems = ko.observable();

        //update it when the observableArray is updated
        this.subscribe(function (newValue) {
            this.hasItems(newValue && newValue.length);
        }, this);

        //trigger change to initialize the value
        this.valueHasMutated();

        //support chaining by returning the array
        return this;
    };