Javascript code working on JsFiddle but not working on my host

<!DOCTYPE html>
<html>
<head>
    <meta http-equiv="content-type" content="text/html; charset=UTF-8">
    <title>Title</title>
</head>
<body>
<script>
// Detect private browsing
// Inpired by original gist: https://gist.github.com/cou929/7973956
// But based in general on comment: https://gist.github.com/cou929/7973956#gistcomment-1791792 and other comments
(function (window) {
    var on, off;

    function Webkit() {
        if (window.webkitRequestFileSystem) {
            window.webkitRequestFileSystem(window.TEMPORARY, 1, off, on);
            return true;
        }
    }

    function Mozilla() {
        if ('MozAppearance' in document.documentElement.style) {
            const db = indexedDB.open('test');
            db.onerror = on;
            db.onsuccess = off;
            return true;
        }
    }

    function Safari() {
        if (/constructor/i.test(window.HTMLElement)) {
            // iOS 11
            // Origin: https://gist.github.com/cou929/7973956#gistcomment-2272103
            try {
                window.openDatabase(null, null, null, null);
            } catch (e) {
                on();
            }

            // Older Safari
            try {
                if (localStorage.length)
                    off();
                else {
                    localStorage.x = 1;
                    localStorage.removeItem('x');
                    off();
                }
            } catch (e) {
                // Original gist: https://gist.github.com/jherax/a81c8c132d09cc354a0e2cb911841ff1

                // Safari only enables cookie in private mode
                // if cookie is disabled then all client side storage is disabled
                // if all client side storage is disabled, then there is no point
                // in using private mode
                navigator.cookieEnabled ? on() : off();
            }

            return true;
        }
    }

    function IE10Edge() {
        if (!window.indexedDB && (window.PointerEvent || window.MSPointerEvent)) {
            on();
            return true;
        }
    }

    window.isPrivate = function (on_cb, off_cb) {
        on = on_cb || function () {};
        off = off_cb || function () {};
        Webkit() || Mozilla() || Safari() || IE10Edge() || off();
    };
})(window);

isPrivate(
    function () {document.body.innerHTML = 'Private browsing: <b>ON</b>'},
    function () {document.body.innerHTML = 'Private browsing: <b>OFF</b>'}
);


</script>
</body>
</html>