magento实时更新购物车商品数量

<td>
<button οnclick="addQtyone();" type="submit">+</button>
<input id="qtyPro" name="cart[<?php echo $_item->getId() ?>][qty]" value="<?php echo $this->getQty() ?>" size="4" title="<?php echo $this->__('Qty') ?>" maxlength="12" />
<button type="submit" οnclick="redQtyone();">-</button>
<div></div>
</td>
<script type="text/javascript">
function addQtyone()
{var qtyPro=$('qtyPro');qtyPro.value = parseInt(qtyPro.value)+1;
}
function redQtyone()
{var qtyPro=$('qtyPro');qtyPro.value = parseInt(qtyPro.value)-1;
}
</script>