JSFiddle - React, Tailwind, and code Playground

JavaScript

var start, end, elapsed;

document.addEventListener("DOMContentLoaded", function() {
	
	start = new Date().getTime();
	
	window.addEventListener("unload", function() {

		end = new Date().getTime();
		elapsed = (end - start) / 1000;
		
		console.log(elapsed);

	});
	
});