gistfile1.js

// undeclared function you need to declare:
// cb(data): fired when new data from the stream is available.
//           data is the updated line. use JSON.parse to parse data.
// hungup(): fired when the user stream is disconnected.
//           this function needs to handle it. maybe retry or display error.

// undeclared variables you need to declare.
// url:      user stream's url endpoint.

var xh = new XMLHttpRequest();
var llen = 0;
var ltime = 0;
var buffer = '';
var itvid;
var hungup = false;
function rsc() {
	if (xh.readyState == 4) {
		hangup ();
	}
}
function hangup() {
	if (!hungup) {
		window.clearTimeout (itvid);
		hung ();
	}
	hungup = true;
}
function line(data) {
	ltime = new Date().getTime();
	if (data == '') {
		return;
	}
	cb (data);
}
function itv() {
	if (new Date().getTime() - ltime > 90000) {
		hangup ();
		xh.abort ();
	}
	if (llen != xh.responseText.length) {
		buffer += xh.responseText.substr(llen);
		var npos = buffer.indexOf('\n');
		while (npos > -1) {
			line (buffer.substr(0, npos));
			buffer = buffer.substr(npos + 1);
			npos = buffer.indexOf('\n');
		}
		llen = xh.responseText.length;
	}
}
xh.open ('GET', url, true);
xh.onreadystatechange = rsc;
xh.send ('');
ltime = new Date().getTime();
itvid = window.setInterval (itv, 100);

Oops! I mean "hung()" instead of "hungup()". Hungup is a variable to keep track of the state. My bad~