Ошибка подгрузки товаров в корзину

Реализована карточка товара на Vue, однако если внутри товара не найден класс product-type, появляется ошибка и скрипты не отрабатывают. Очень хочу понять, что я упустил

  "use strict"

  if (document.querySelector('.product-type')) {
    let tableProductTypesToArray = (table) => {

      let tableRows = table.querySelectorAll('tr');

      let productName = document.getElementById('main-name').value;

      let productTypes = [];

      for (let i = 0; i < tableRows.length; i++) {
        const last = tableRows[i].querySelectorAll('td').length-1;
        productTypes.push(
          {
            name: productName + tableRows[i].querySelectorAll('td')[0].innerHTML,
            price: tableRows[i].querySelectorAll('td')[last].innerHTML,
            quantity: 0,
          }
        );
      };
      return productTypes;
    };

    let changeCells = (table) => {
      let tableRows = table.querySelectorAll('tr');

      for (let i = 0; i < tableRows.length; i++) {
        const last = tableRows[i].querySelectorAll('td').length-1;
        const cellPrice = tableRows[i].querySelectorAll('td')[last];
        cellPrice.innerHTML === 'по запросу' ? '' : cellPrice.innerHTML += ' руб.';

        let cellQuantity = document.createElement('td');
        cellQuantity.setAttribute('item', i);
        cellQuantity.innerHTML =
        `
          <div class="quantity">
            <button @click="quantityMinus(${i})" class="quantity__btn">-</button>
            <input @input="quantityInput(${i})" v-model="product.productTypes[${i}].quantity" class="quantity__number" type="text" name="" value="{{ product.productTypes[${i}].quantity }}">
            <button @click="quantityPlus(${i})" class="quantity__btn">+</button>
            <button @click="addToCart(${i})" class="quantity__btn">
              <i class="fa fa-2x fa-cart-arrow-down"></i>
            </button>
          </div>
        `;

        tableRows[i].appendChild(cellQuantity);
      };
    };

    const tableProductTypes = document.querySelector('.product-type').querySelector('table');
    var productTypes = tableProductTypesToArray(tableProductTypes);
    changeCells(tableProductTypes);
  } else {
    var productTypes = [];
  }

  let cart = new Vue({
      el: '.page-content',
      // props: ['productTypes'],
      data: {
        product: {
          name: '',
          productTypes: productTypes,
        },

        cart: [],
        isCartVisible: false,
        cartNumber: 0,

      },
      mounted() {
        if (localStorage.cart) {
          this.cart = JSON.parse(localStorage.getItem('cart'));
        }
      },
      methods: {
        quantityPlus(item) {
          this.product.productTypes[item].quantity++;
        },

        quantityMinus(item) {
          if(this.product.productTypes[item].quantity >= 1) {
            this.product.productTypes[item].quantity--;
          };
        },

        quantityInput(item) {
          if(this.product.productTypes[item].quantity < 0 || this.product.productTypes[item].quantity === '') {
            this.product.productTypes[item].quantity = 0;
          };
        },

        localStorage() {
          return JSON.parse(localStorage.getItem('cart'))
        },

        addToCart(item) {
          if (this.product.productTypes[item].quantity >= 1) {
            if( this.cart.indexOf(this.product.productTypes[item]) === -1 ) {
              this.cart.push(this.product.productTypes[item]);
            } 
          };
          this.cart.concat(this.localStorage());
        },

        deleteCartItem(item) {
          this.cart.splice(item, 1);
        },
        summCartItem(price, quantity){

          var linePrice = price*quantity;

          if (isNaN(linePrice)) {
            return "по запросу";
          } else {
            return linePrice.toFixed(2);
          }
        },
      },
      computed: {
        getCart() {
          this.cart = JSON.parse(localStorage.getItem('cart'));
        },
        isCartEmpty() {
          if (this.cart.length <= 0) {
            return true
          } else {
            return false
          }
        },
      },

      watch: {
        cart(newCart) {
          newCart = JSON.stringify(newCart);
          localStorage.setItem('cart', newCart);
        }
      },
    });