what problem my code ?
I actually want to reduce and increase the quantity of some items from one button but I can't understand what is wrong with the code. So I'm here to help. Please help anyone. Thank you

 **server side**
        
        ** PUT METHODS**
            app.put("/items/:id", async (req, res) => {
              const id = req.params.id;
              const updateItemData = req.body;
              const filter = { _id: ObjectId(id) };
              const option = { upsert: true };
              const updateItemDoc = {
                $set: {
                  quantity: updateItemData.itemQuantity,
                },
              };
              const result = await itemsCollection.updateOne(
                filter,
                option,
                updateItemDoc
              );
        
              res.send(result);
            });
          } finally {
          }
        };
        **client side**`enter code here`
         useEffect(() => {
            fetch(`http://localhost:5000/items/${itemId}`)
              .then((response) => response.json())
              .then((data) => setItem(data));
          }, []);
        
          const handleItemDelivered = (quantity) => {
            const newQuantity = item.quantity - 1;
            console.log(newQuantity);
            const { itemQuantity } = newQuantity;
            console.log(parseInt(newQuantity));
            const url = `http://localhost:5000/items/${itemId}`;
            fetch(url, {
              method: "PUT",
              headers: {
                "content-type": "application/json",
              },
              body: JSON.stringify(itemQuantity),
            })
              .then((response) => response.json())
              .then((datenter code herea) => setItem(data));
            alert("quantity-updated successfully");
          };

CodePudding user response：

Since you are increasing and decreasing the count, the best practice is to use $inc instead of $set. This is an atomic operation that will allow you update from several clients "on parallel", i.e., they will not override each-other:

const updateItemDoc = {
                $inc: {
                  quantity: updateItemData.deltaQuantity,
                },
              };