JSFiddle - React, Tailwind, and code Playground

HTML

<div id="box"></div>

CSS

#box {
  width: 100px;
  height: 100px;
  background-color: blue;  
}

JavaScript

setTimeout(function() {
    alert(1)
  var box = document.getElementById('box');
  box.style.backgroundColor = 'red';

  var start = new Date;
  while (new Date - start < 1000) {
    // wait 1 second...
  };
}, 0);