var launchInterval = -1;
var launchCounter = 1;
var launchCountdownNumberElement = null;
var launchCountdownProgressElement = null;

function launchTick() {
	launchCountdownNumberElement.innerText = "" + Math.floor(6.0 - launchCounter * 0.06);
	launchCountdownProgressElement.style.width = "" + launchCounter + "%";
	if(++launchCounter > 100) {
		clearInterval(launchInterval);
		setTimeout(() => { document.getElementById("launch_countdown_screen").remove(); main(); }, 50);
	}
}

window.addEventListener("load", () => {
	launchCountdownNumberElement = document.getElementById("launchCountdownNumber");
	launchCountdownProgressElement = document.getElementById("launchCountdownProgress");
	launchInterval = setInterval(launchTick, 50);
});

<div style="margin:0px;width:100%;height:100%;font-family:sans-serif;display:flex;align-items:center;user-select:none;" id="launch_countdown_screen">
<div style="margin:auto;text-align:center;">
<h1>This file is from <span style="color:#AA0000;">${date}</span></h1>
<h2>Game will launch in <span id="launchCountdownNumber">5</span>...</h2>
<div style="border:2px solid black;width:100%;height:15px;padding:1px;margin-bottom:20vh;"><div id="launchCountdownProgress" style="background-color:#555555;width:0%;height:100%;"></div></div>
</div>
</div>