var checkerInf = null;

function checkerGet(url) { 
	if (checkerInf) {
		if (checkerInf.readyState < 4) { 
			return(0); // busy
		}
	}

	if (window.XMLHttpRequest) checkerInf = new XMLHttpRequest();
	else if (window.ActiveXObject) checkerInf = new ActiveXObject("Microsoft.XMLHTTP");

	if (checkerInf) {
		checkerInf.onreadystatechange = checkerProcess;
		checkerInf.open("GET", url, true); 
		checkerInf.send(null);
		return 1;
	}
	else return 0;
}

function checkerProcess() { 
	if (checkerInf) {
		if (checkerInf.readyState == 4) {
			if (checkerInf.status == 200) { 
				// do whatever
			}  
		} 
	}
}