JSFiddle - React, Tailwind, and code Playground

HTML

<div id="loading">
Loading
</div>

JavaScript

var loading = document.getElementById("loading");

function hideLoadingWhenDone() {
  requestAnimationFrame(function() {
    console.log("Animation done.");
    loading.style.display = "none";
  });
}

var n = 0;
var N = 150000;
var digits = "";
mO = new MutationObserver(
	function(mutations)
	{
		console.log("Mutations observed.");
	}
);
mO.observe(document.body, { childList: true });

while (n < N)
{
	span = document.createElement("span");
	digit = parseInt(Math.random() * 10);
	span.innerHTML = digit;
	if (digits.length < 3)
	{
		digits += digit;
	}
	document.body.appendChild(span);
	n++;
}

console.log("Finished with digits " + digits);

hideLoadingWhenDone();