JSFiddle - React, Tailwind, and code Playground

HTML

<div id="div1" class="aaw" style="z-index:200" >div-1kjkjkkjjk</div>
<div id="div2" class="aaw">div-2</div>
<div id="div3" class="aaw">div-3</div>
<div id="div4" class="aaw">div-4</div>

<div id="e">9</div>

CSS

#div1 { z-index: 1; background:#000; color:#fff }
#div2 { z-index: 2 }
#div3 { z-index: 5 }
#div4 { z-index: 10}

JavaScript

$(document).ready( function() {
var highestzindex = 0; 
var resultelement = null;  
$(".aaw").each(function() {
    var currentzindex = parseInt($(this).css("zIndex"), 10);
  if(currentzindex > highestzindex) {
        highestzindex = currentzindex;
        resultelement = $(this);
    }
});
    
    $("#e").html( $(resultelement).text());
    $("#div4").append("<br/><b>The highest element has z-index :" + $(resultelement).text() + "</b>");
});