JSFiddle - React, Tailwind, and code Playground

HTML

<div class="res"></div>
<div class="div">1</div>
<div class="div">2</div>
<div class="div">3</div>
<div class="div">4</div>
<div class="div">5</div>
<div class="div">6</div>
<div class="div">7</div>
<div class="div">8</div>
<div class="div">9</div>
<div class="div">10</div>

CSS

.res{
  height: 50px;
}
.div{}

JavaScript

var res = document.querySelector('.res');
var arrElem = document.querySelectorAll('.div');
var arrayElem = [];

for (var i = 0; i < arrElem.length; i++){
  arrayElem.push(arrElem[i]);
  arrElem[i].addEventListener('click', function(e){
     res.innerHTML = arrayElem.indexOf(e.target);
  });
}