Javascript AJAX和Codeigniter-确定按下哪个按钮进行更新

我有这个购物车，我可以添加或减少特定项目的数量。问题是我不知道如何确定用户是按了加号按钮还是减号按钮

加号/减号的HTML代码

<td>
   <div class="input-group" style="width: 100px !important;">
      <span class="input-group-btn">
         <button class="btn btn-danger btn-minus" type="button">-</button>
      </span>
      <input class="form-control table-shopping-qty" type="text" id = "<?php echo $cartrow['id']?>" value="<?php echo $cartrow['qty']?>" style="padding-left:5px;text-align: center;"/>
      <span class="input-group-btn">
         <button class="btn btn-success btn-plus" type="button">+</button>
      </span>
   </div><!-- /input-group -->
</td>

---

在控制器中加载

url

帮助程序。使用

$this->load->url（'url'），然后

function updateShoppingCart(){
var productid = $(".table-shopping-qty").attr("id");
dataString = {productid: productid};

$.ajax({
  type: "POST",
  url: "<?php echo base_url('listproductscontroller/editcart_item');?>",
  data: dataString,
  cache: false,
  success: function(data){
    alert("success");
  }, error: function(){
    alert("failed");
  }
});

到目前为止，我已经尝试获取它的ID，但由于它取决于会话，而不是添加/减去的数量本身，因此我遇到了获取其值的问题
public function editcart_item(){
  $id = $this->input->post('productid');

  if($this->session->userdata('cartsession')){
    $cartsession = $this->session->userdata('cartsession');
    foreach($cartsession as $row){
      if($row['id'] == $id){
        $updated = array('id'=>$row['id'], 'qty'=>$row['qty'] - 1);
      }else{
        $updated = array('id'=>$row['id'], 'qty'=>$row['qty']);
      }
    }
    $this->session->set_userdata('cartsession', $updated);
  }

  if($this->session->userdata('cartsession')!=NULL){
    if($this->cartdata = $this->ProductModel->getProductToCart($this->session->userdata('cartsession'))){
      $this->session->set_userdata('globalcart', $this->cartdata);
    }
  }
}

function updateShoppingCart(){
var productid = $(".table-shopping-qty").attr("id");
dataString = {productid: productid};

$.ajax({
  type: "POST",
  url: "<?php echo base_url('listproductscontroller/editcart_item');?>",
  data: dataString,
  cache: false,
  success: function(data){
    alert("success");
  }, error: function(){
    alert("failed");
  }
});

$_config['base_url'] ="your_domain_name";