function ajax( method, url, onSuccess, onError ) { 
    var httpRequest;
    if( window.XMLHttpRequest ) httpRequest = new XMLHttpRequest();
    else if( window.ActiveXObject ) httpRequest = new ActiveXObject("Microsoft.XMLHTTP");
    httpRequest.onreadystatechange = function() {
		if( httpRequest.readyState == 4 ) {
	    	if( httpRequest.status == 200 ) onSuccess( httpRequest );
	    	else onError( httpRequest );
		}
		else onSuccess( httpRequest, 'loading' );
    }
    httpRequest.open(method, url, true);
    httpRequest.send(null);
}