localstorage item value resetting

I have javascript code below

let beer_JSON = {"name": "beer", "price": 2.99, "quantity": 0};

let beer = document.getElementById("beer");

function alert(){
    Swal.fire({
         position: 'top-end',
         icon: 'success',
         title: 'added',
         showConfirmButton: false,
         timer: 1500
       });
 }

    beer.addEventListener("click", function() {
        alert();
        beer_JSON.quantity++;
        localStorage.setItem('beer', JSON.stringify(beer_JSON));
      });

My quantity value resets to 0 after page refreshes. How can I fix that

>Solution :

This code executes every time page refreshes and resets quantity.

let beer_JSON = {"name": "beer", "price": 2.99, "quantity": 0};

You need to get this initial data from localStorage. Replace the first line with this code.

let beer_JSON = JSON.parse(localStorage.getItem("beer")) || {"name": "beer", "price": 2.99, "quantity": 0};