JSFiddle - React, Tailwind, and code Playground

HTML

<button type="button" class="btn" data-price="12">Кнопка 1</button>
<button type="button" class="btn" data-price="9">Кнопка 2</button>
<button type="button" class="btn" data-price="3">Кнопка 3</button>

JavaScript

var price = 0;
function calculate(plus)
{
  plus = parseInt(plus);
  price += plus;
  console.log(price);
}

$(document).ready(function()
{
  $('.btn').on('click', function()
  {
    console.log($(this));
    var plus = $(this).attr('data-price');
    calculate(plus);
  });
});