gistfile1.txt

function ajax(m, url) {
  var r = new XMLHttpRequest();
	r.open(m, url);
	r.header = r.setRequestHeader;

	r.basicAuth = function() {
		var s = Array.prototype.slice.call(arguments).join(":");
		r.header("Authorization", "Basic " + btoa(s));
	}

	return r;
}

use.js

var r = ajax("GET", "/topic/" + st.room + "?since=" + st.since);
r.basicAuth(store["sid"]);

function err(e) {
    console.debug("poll: ERROR: ", e);
}

r.addEventLisetner("error", err);

r.addEventLisetner("load", function() {
	switch (r.status) {
		case 200:
			doSuccess();
		case 401:
			showLogin();
			break;
		case 404:
			alert("not found!");
			break;
		default:
			err();
			break;
	}
});

r.send();