Ken's Solution

const calculateTotal = () => {
    // Assume this your cart.
    let cartArr = [
      {
        'price': 1000,
        'quantity': 12
      },
      {
        'price': 2000,
        'quantity': 22
      },
      {
        'price': 3000,
        'quantity': 32
      }
    ];
    
    let grandTotal = 0;
    cartArr.forEach(function (cartItem) {
      let productTotal = cartItem.price * cartItem.quantity;
      grandTotal += productTotal;
      console.log(productTotal);
      console.log(grandTotal);
    });
}
  
  console.log(calculateTotal())