JS project related issues

if (points === 4 && cartItems.find(p => p.productId === cartItems.productId))

var itemID = document.getElementById("addItemId").value;

function cartItem(productId, price, quantity, shipping) {
        this.productId = productId; // String the id of the product
        this.price = price; // Float – the price of the item
        this.quantity = quantity; // Int – the amount of this product in the cart
        this.shipping = shipping; // Float – cost of shipping for this item
    }

    // Global Empty Arrays to contain our objects of Store Items and Cart Items that will be created through the constructor
    let storeItems = [];
    let cartItems = []; 

        if (points === 4 && cartItems.find(p => p.productId === itemID)) {
            productId.quantity++;
            alert("Successful incremented purchase of the Timepiece");
        } else {
            cartItems.push(new cartItem(itemID, obj[0].price, quantityCart, obj[0].costOfShipping));
        } 

function addToCart() {

        var itemID = document.getElementById("addItemId").value;
        var itemIDColor = document.getElementById("addItemId");
        let itemQty = document.getElementById("addItemQty");
        var addQtyValidationMessage = document.getElementById("addQtyValidationMessage");
        var outputErrorQty = document.createElement('p');



        // iterating and validating if item actually exists in our storeItems array, Loved this .filter ES6 method so helpful to iterate and compare in one line
        let obj = storeItems.filter(x => { return x.productId === itemID });
        console.log(itemID);
        console.log(obj);


        let quantityCart = parseInt(document.getElementById("addItemQty").value);

        let points = 0;

        //VALIDATIONS inside the addtoCart function immediately without a seperate validation function

        if (Number.isInteger(quantityCart)) {
            points++;
        } else {
            itemQty.style.borderColor = "#FF0000";
            alert("Please insert the correct number into blank space!");
            outputErrorQty.innerText += 'Please insert the correct number into blank space!';
            addQtyValidationMessage.appendChild(outputErrorQty);
            outputErrorQty.className = "outputProductErNumber"
        }

        if (quantityCart <= 0) {
            alert('Enter an integer number please!');
            itemQty.style.borderColor = "#FF0000";
            outputErrorQty.innerText += 'Enter an integer number please!';
            addQtyValidationMessage.appendChild(outputErrorQty);
            outputErrorQty.className = "outputProductErNumber";
        } else {
            points++;
        }


        if (quantityCart > obj[0].maxPerCustomer) {
            alert(`Unfortunately, We can't let you buy so many timepieces as they're Limited editions`);
            itemQty.style.borderColor = "#FF0000";
            outputErrorQty.innerText += `Unfortunately, We can't let you buy so many timepieces as they're Limited editions`;
            addQtyValidationMessage.appendChild(outputErrorQty);
            outputErrorQty.className = "outputProductErNumber";
        } else {
            points++;
        }
        // When I run the line 1054 add more items than quantity, it triggers first the 1049 line alert and then the alert of 1055 line
        if (quantityCart > obj[0].quantity) {
            alert(`Unfortunately, We don't have these many watches available in stock `);
            itemQty.style.borderColor = "#FF0000";
            outputErrorQty.innerText += `Unfortunately, We don't have these many watches available in stock `;
            addQtyValidationMessage.appendChild(outputErrorQty);
            outputErrorQty.className = "outputProductErNumber";
        } else {
            points++;
        }

        /*
        if (points === 4) {
            alert("Successful purchase of the Timepiece");
            cartItems.push(new cartItem(itemID, obj[0].price, quantityCart, obj[0].costOfShipping));
            itemIDColor.style.borderColor = "#008000";
            itemQty.style.borderColor = "#008000";
        }
*/

        if (points === 4 && cartItems.find(p => p.productId === itemID)) {
            cartItems[0].quantity++;
            console.log(cartItems.quantity);
            alert("Successful incremented purchase of the Timepiece");
        } else {
            cartItems.push(new cartItem(itemID, obj[0].price, quantityCart, obj[0].costOfShipping));
        }


        console.log(cartItems);
        //Calling the function to display the added Items in the cart
        displayCartItems();
        // calling calculate function here
        calculateCartTotals();

    } // end of the main function   ``` I seem to have understood it now with ur explanation even if late) Now it increments every item in the cart) THe only problem now. The other earlier conditions don't seem to work. Let's say maxpercustomer is 3 but now it adds the 4 items if this item is in the cart. If item is not in the cart the conditions work

if (points === 4) {
            alert("Successful purchase of the Timepiece");
            cartItems.push(new cartItem(itemID, obj[0].price, quantityCart, obj[0].costOfShipping));
            itemIDColor.style.borderColor = "#008000";
            itemQty.style.borderColor = "#008000";
        }``` When  I use my old code like this even if index is 0 in other test conditionals , and i'm adding second, thrid item to the cart, the conditionals work and don'tt add the wrong amount of items to the cart. But when I use the latest .find method then it just adds -1 0 88 like all the invalid numbers. Though when I use my first code in spite of 0 index all the conditional work. What's the reason that it works still with zeros? And what would be the best way to fix the code with the find solution?