quantity.js | quantity | Parser library

I want to populate state like this:

With the help of a user here I was able to make a component, however now I need a variation of that component. The component is an increment / decrement button with some details:
1 - The button is in an array coming from an API
2 - The increment / decrement must follow a rule defined in the bank, that is, a maximum number of items
3 - A footer with the Buy button should appear automatically when one of the items exists
4 - When I click the Buy button, the items will be saved in the localStorage and a new screen will open, called a shopping cart that will contain the same increment / decrement buttons but with the items saved in the localStorage selected in the list and the buttons should increment / decrement the items and clicking the Confirm Purchase button the localStorage must be updated.
Until item 3 and half of item 4 I was able to do, but I'm having problem with the increment / decrement buttons. Below is the code for my components

I got a component that is render in a array. This component just show 2 buttons and a input text. This buttons increment/decrease 1 item (see the image). I have some data coming from a API and one of this item limit the purchase. I need to hide the increment button when the limit is higher and show when limit is lower. I can do this, but my problem is that just occur with one button and not with all the buttons in array

I am following the book Agile Web Development with Rails 5.1 and am in Chapter 11 where I am trying to create a button that decrements the quantity of an item within my cart. I am trying to use ajax to solve this and calling the render method on the cart. I am getting the following error...

ActionView::Template::Error ('nil' is not an ActiveModel-compatible object. It must implement :to_partial_path.): 1: cart = document.getElementById("cart") 2: cart.innerHTML = "<%= j render(@cart) %>"

the button that this ajax calls originates from is a partial if that changes anything. I am new to rails and am stuck.

decrement_quantity.js.coffee