How can I decrease the price using the same number used to increase?

Question

I'm trying to decrease the price when the user presses the minus icon using the initial price, but then the new price after increasing is the initial price

quantityHandler: function (action, product) {
      // Increase or decrease quantity of product
      try {
        const newItems = [...this.products]; // clone the array
        let idx = newItems.indexOf(product);
        let currentQty = newItems[idx].productQuantity;
        let price = newItems[idx].unitPrice;

        if (action == "more") {
          newItems[idx].productQuantity = currentQty + 1;
          newItems[idx].unitPrice = price + price;
        } else if (action == "less") {
          newItems[idx].productQuantity = currentQty > 1 ? currentQty - 1 : 1;
          // Decrease current price using the initial price
        }

        this.products = newItems; // set new state
        console.log(this.products);
      } catch (error) {
        alert(error);
      }
    },

Answer 1

quantityHandler: function (action, product) {
      // Increase or decrease quantity of product
      try {
        const newItems = [...this.products]; // clone the array
        let idx = newItems.findIndex((item) => { //compare with some unique identifier
         return item.id === product.id
        })
        let currentQty = newItems[idx].productQuantity;
        let price = newItems[idx].unitPrice;
        let perQtyPrice = price / currentQty  //per unit price
        if (action == "more") {
          newItems[idx].unitPrice += perQtyPrice;
          newItems[idx].productQuantity = currentQty + 1;
        } else if (action == "less") {
          if(currentQty > 1) {
           newItems[idx].unitPrice -= perQtyPrice;
           newItems[idx].productQuantity = currentQty > 1 ? currentQty - 1 : 1;
          }
        }

        this.products = newItems; // set new state
        console.log(this.products);
      } catch (error) {
        alert(error);
      }
    },

You need to find the per item price then use that to subtract or add to the price