var updates = new XMLHttpRequest();
updates.onreadystatechange = function(){
    "use strict";
    if(updates.readyState === 4 && updates.status === 200){
        console.log(updates.responseXML);
    }
};

var timer = 0;
clearInterval(timer);
timer = setInterval(function(){
    "use strict";
    updates.open('GET','scripts/check_for_notifications.php', true);
    updates.send();
},2000);

$response = new SimpleXMLElement('<xml/>');

$update = $response->addChild('update');
$update->addChild('content', 'New message');
$update->addChild('redirect', 'some link');
$update->addChild('date', '1.1.2019 12:00');

header('Content-type: text/xml');
print($response->asXML());

updates.open('GET','scripts/check_for_notifications.php&nocache=' + new Date().getTime(), true);