function buy(id) {
    var req = new JsHttpRequest();
    req.loader="FORM";
    req.onreadystatechange = function() {
        if (req.readyState == 4) {
  	    if (req.responseJS.num != null) document.getElementById('basket_num').innerHTML = req.responseJS.num;
  	    if (req.responseJS.summ != null) document.getElementById('basket_summ').innerHTML = req.responseJS.summ;
	    alert('Товар добавлен в корзину');
        }
    }
    req.open("POST", 'buy.php', true);
    req.send({ 'buy': id});
};