JSFiddle - React, Tailwind, and code Playground

HTML

<div class="quantity" id="product1">
  <input style="font-size:21px;" type="button" value="-" onclick='javascript:     document.getElementById("number").value--;' class="operator">
  <input id="number" type="number" value="" class="qty" name="picpac">
   <input style="font-size:21px;" type="button" value="+"  onclick='javascript:     document.getElementById("number").value++;'  class="operator">
</div>

<input type="hidden" id="product1_base_price" value="10">

<div id="product1_total_price">
  0
</div>

JavaScript

$(document).ready(function() {

  $(".operator").on('click',function() {
      $("#product1_total_price").text($("#product1_base_price").val() * $("#number").val());
  });
});