var currentPos = 0;
    timer = window.setInterval(function() {
        if (xhr.readyState == XMLHttpRequest.DONE) {
            window.clearTimeout(timer);
            $('body').append('done <br />');
        }
        $('body').append('state: ' + xhr.readyState + '<br />');
        var text = xhr.responseText;
        console.log(text.substring(currentPos));
        $('body').append('data: ' + text.substring(currentPos) + '<br />');
        currentPos = text.length;
    }, 1000);