ถ้าเราจะเชคว่า ถ้าในตระกร้าสินค้ามีรายการ $item_code อยู่แล้ว ห้ามกด Add to cart ให้ alert

$item_code = $obResult['item_code'];

if($id == '13'){
echo "<button class='btn btn-primary btn-xs ' type='button' onclick='cart_click($item_id,$id,$pr_id,$item_code)' name='regisBtn' id='regisBtn' >Add to cart </button>" ;
}else if($ven != ''){
 echo "<button class='btn btn-primary btn-xs ' type='button' onclick='cart_click($item_id,$id,$pr_id,$item_code)' name='regisBtn' id='regisBtn' >Add to cart </button>" ;
}

<script type="text/javascript">
function cart_click(id,g_id,pr_id,item_code){
  var item_id = id;
  var group_id= g_id;
  var pr_id  = pr_id;
  var item_code = item_code;
  swal({
    title: "Please Fill QTY",
    type: "input",
    showCancelButton: true,
    closeOnConfirm: false,
    animation: "slide-from-top",
    inputPlaceholder: "QTY"
  },
  function(inputValue)
  {
    if (inputValue === false) return false;
    if (inputValue === "") {
      swal.showInputError("Please Fill Quantity");
      return false
    }
    $.post("Action/action.php?op=add_item_pr",{'item_id':item_id,'qty':inputValue,'group_id':group_id,'pr_id':pr_id},
      function(data)
      {
          alert(data);
          if(data!="")
          {
            var pr_id = data;
            swal("ADD Item Finnish", "QTY: " + inputValue, "success");
            setTimeout(function() {
              window.opener.location.href='index.php?page=predit'+'&pr_id='+pr_id   
            }, 1500);
            setTimeout(function() {
              window.opener=null;window.close() 
            }, 50000);
        }else{
            swal("Item already Select!!", "Please Type Again", "error");
        }
      }
      );
  });
 $(".sweet-alert").on('keypress',function(event){
var arr = [ "."];
var regex = new RegExp("^[0-9]+$");
var key = String.fromCharCode(!event.charCode ? event.which : event.charCode);
var pos = jQuery.inArray( key, arr );
var data = $(this).val().toString();
var arrsplit = data.split('.');
var cntSplit = arrsplit.length;
if (!regex.test(key) &&  pos == "-1" ) {
  event.preventDefault();
  return false;
}else{
  if(cntSplit > 1 && key =="."){
    event.preventDefault();
    return false;
  }
}
});
}
function fncOpenPopup(val)
{
  window.location ='index.php?page=add_pricel';
}
$(function(){
  $('#table_id').DataTable();
  $("#btn_cancel").click(function(){
    location.reload();
  });
});
</script>