function hasClass( elem, klass ) {
     return (" " + elem.className + " " ).indexOf( " "+klass+" " ) > -1;
}

function checkModernBrowser() {
	var element = document.getElementById('html');
	var splashEl = document.getElementById('upgrade-browser');

	if (!(hasClass(element, "backgroundsize"))) {
		console.log("old browser");
		splashEl.style.display = "block";
	} 
}

window.onload = function() {
	checkModernBrowser();
}