YAHOO.util.Event.onDOMReady(function (ev) {
    var YDom = YAHOO.util.Dom;
    var YEvent = YAHOO.util.Event;

    var aUnits = YDom.getElementsBy(function (oElem) {
        return oElem.type == 'radio';
    }, 'input', 'cart_quantity');
    YEvent.on(aUnits, 'click', function () {
        this.form.submit();
    });
});