JSFiddle - React, Tailwind, and code Playground

HTML

Product 1: <button id="product1">Add one</button>
<br>
Product 2: <button id="product2">Add one</button>
    
<div></div>

JavaScript

var cart = new Array();

$(document).ready(function(){
    
$('button').on('click', function() {
			var pid = $(this).attr('id');

			cart[cart.length] = {id:pid, qty:1}

			var result = cart.reduce(function(res, obj) {
					if (!(obj.id in res))
						res.__array.push(res[obj.id] = obj);
					else {
						res[obj.id].qty += obj.qty;
					}
					return res;
				}, {__array:[]})
       
            console.log(result)
	});
});