Magento 2 – Get cart item qty change in Javascript

I have a javascript file that loads when the page loads. This file defines two variables (one for the shopping cart items and one for the count).

This script also contains a subscribe that fires whenever the cart is updated.

When I add items to the cart, remove items from the cart or update the cart, this subscribe is hit and I am able to execute logic inside there.

This is fine for most however when a user changes the qty of an item in the cart, I can never get the previous qty.

var cart = customerData.get('cart');

    // Define variables to check against inside the subscribe
    var count = cart().summary_count;
    var currentItems = [...cart().items];

    // Watch the cart
    cart.subscribe(function () {
        // If the count has changed
        if (cart().summary_count !== count) {  
                for(let i =0; i < cart().summary_count; i++){
                    var foundItem = currentItems.find(x => x.product_id == cart().items[i].product_id);
                    var currentItem = cart().items[i];

                    // Both of these values are the same
                    if(foundItem.qty < currentItem.qty){
                        var qtyChange = currentItem.qty - foundItem.qty;
                    }
                }
        }

        // Set the count to the new value
        count = cart().summary_count;

        // Set the new currentItems array
        currentItems = cart().items;
    });

The cart().summary_count updates but the qty against the item updates in both the duplicated items array defined outside the subscribe as well as the cart().items array (which I’d expect).

I have noticed that the value for qty in the array defined outside the subscribe changes to a string and the cart().items version of the qty is an int.

Below is a screenshot of what I am seeing in dev tools. I have updated the qty in the cart for item_id 269

Am I missing something here?