I manage to add in two more field into order line. When user click to change these fields, I need the system to auto calculate base on these two fields and update the quantity field. I am new to javascript, not able to get it work. Thank a lot.

All I know is the following code will update the field whenever user click on the numpad. But I am not manage to tweak it.

setValue: function(val) {
            /*
            var param = {};
            param[this.numpadState.get('mode')] = val;
            var order = this.shop.get('selectedOrder');
            if (order.get('orderLines').length !== 0) {
               order.selected.set(param);

            } else {
                this.shop.get('selectedOrder').destroy();
            }
        },