JSFiddle - React, Tailwind, and code Playground

HTML

<div id="container">
  <div class="item">...</div>
  <div class="item">...</div>
  <div class="item">...</div>
  <div class="item">...</div>
</div>

JavaScript

function randomDiv() {
    var divCount = $(".item").length;
    var randomnumber=Math.floor(Math.random()*divCount);
    
    $("div.item:eq(" + randomnumber + ")").after("<div class='randomDiv'>hey im random</div>");
}

randomDiv();