Javascript – keep getting TypeError: array.push is not a function when trying to push an object into an existing array with objects

I’m learning about localStorage and I’m trying to build a basic shopping cart function. The process is:

1. user clicks on "Add To Cart" button.
2. If localStorage("shoppingCart") doesn’t exist, then localStorage.setItem("shoppingCart", itemToAdd).
3. If localStorage("ShoppingCart) DOES exist (which for testing purposes, it does) then bring in the JSON string and parse it into an initialized array called updatedShoppingCart = [];
4. clear the localStorage,
5. push the itemToAdd object to the updatedShoppingCart array.
6. Then set the updatedShoppingCart array to local storage with localStorage.setItem("shoppingCart", JSON.stringify(updatedShoppingCart)) for later usage in shopping process.

but I keep getting the TypeError: updatedShoppingCartArray.push is not a function
at HTMLButtonElement.addToCart error on step #5.

Here’s my code:

// simulate a product in the localStorage.
let prepTesting = {
   name: "Tshirt: Enter the Red Dragon",
   price: 3225,
   qty: 1
};

localStorage.setItem("shoppingCart", JSON.stringify(prepTesting));


// Get values from product index.html page
let order_item_name = document.getElementById('order_item_name');
let order_item_price = document.getElementById('order_item_price');
let order_item_qty = document.getElementById('order_qty');

// initialize buttons
const btn_addToCart = document.getElementById('btn_addToCart');
const btn_clrLocalStorage = document.getElementById('btn_clrLocalStorage');

// set object with product order values
let itemToAdd = {
   name: order_item_name.dataset.name,
   price: parseInt(order_item_price.dataset.price),
   qty: parseInt(order_item_qty.value)
};

function clrLS(e) {
   e.preventDefault();
   localStorage.clear();
   location.reload();
}

function addToCart(e) {
   e.preventDefault();

   // assign localStorage("shoppingCart") to shoppingCart to check if it exists
   let shoppingCart = localStorage.getItem("shoppingCart");

   if (shoppingCart === null) {
      // push itemToAdd to localStorage
      localStorage.setItem("shoppingCart", JSON.stringify(itemToAdd));
   }else {
      // initialize array to insert localStorage array
      let updatedShoppingCartArray = [];

      // get and insert localStorage into updatedShoppingCartArray
      updatedShoppingCartArray = JSON.parse(localStorage.getItem("shoppingCart"));

      // clear localStorage for clean setting.
      localStorage.clear();

      // push itemToAdd into updatedShoppingCartArray
      // This is where I get the "updatedShoppingCartArray.push is not a function" error
      updatedShoppingCartArray.push(itemToAdd); 
      console.log(updatedShoppingCartArray);

      // set updatedShoppingCart to localStorage
      localStorage.setItem("shoppingCart", JSON.stringify(updatedShoppingCartArray));
   }
}

btn_addToCart.addEventListener('click', addToCart);
btn_clrLocalStorage.addEventListener('click', clrLS);

I believe my pseudo-code is correct and I can’t figure out what the issue is with the error when running the script.

Any guidance would be appreciated. Thank you.