Retina replace

retina_replace.js

// retina_replace.js - Maciej Nowakowski <macnow@gmail.com> Twitter: @macnow - more: http://macnow.pl/ios/retina/

function RetinaReplace(){
	function RetinaCheck(el){
		var url = el.src.replace(/\.(gif|png|jpg)$/gi, "_2x.\$1");
		var xmlhttp = new XMLHttpRequest();
		xmlhttp.open("HEAD", url, true);
		xmlhttp.onreadystatechange=function(){
			if(xmlhttp.readyState==4){
				if(xmlhttp.status==200)
				{
					el.width = el.clientWidth;
					el.height = el.clientHeight;
					el.src = url;
				}
			}
		}
		xmlhttp.send(null);
	}
	var RE = document.getElementsByTagName("img");
	for (var i = 0; (el = RE[i]) != null; i++) {
		RetinaCheck(el);
	}
}
onload=function(){
	if( window.devicePixelRatio >= 2 ) RetinaReplace();
}