gistfile1.txt

;(function (callback) {

    function retry(isDone, next) {
        var current_trial = 0, max_retry = 50, interval = 10, is_timeout = false;
        var id = window.setInterval(function() {
            if (isDone()) {
                window.clearInterval(id);
                next(is_timeout);
            }
            if (current_trial++ > max_retry) {
                window.clearInterval(id);
                is_timeout = true;
                next(is_timeout);
            }
        }, 10);
    }

    function isIE10OrLater(user_agent) {
        var ua = user_agent.toLowerCase();
        if (ua.indexOf('msie') === 0 && ua.indexOf('trident') === 0) {
            return false;
        }
        var match = /(?:msie|rv:)\s?([\d\.]+)/.exec(ua);
        if (match && parseInt(match[1], 10) >= 9) {
            return true;
        }
        if (/Edge/.test(window.navigator.userAgent)) {
            return true;
        }
        return false;
    }

    function detectPrivateMode(callback) {

        var is_private;

        if (window.webkitRequestFileSystem) {
            window.webkitRequestFileSystem(
                window.TEMPORARY, 1,
                function() {
                    is_private = false;
                },
                function(e) {
                    console.log(e);
                    is_private = true;
                }
            );
        } else if (window.indexedDB && /Firefox/.test(window.navigator.userAgent)) {
            var db;
            try {
                db = window.indexedDB.open('test');
            } catch(e) {
                is_private = true;
            }

            if (typeof is_private === 'undefined') {
                retry(
                    function isDone() {
                        return db.readyState === 'done' ? true : false;
                    },
                    function next(is_timeout) {
                        if (!is_timeout) {
                            is_private = db.result ? false : true;
                        }
                    }
                );
            }
        } else if (isIE10OrLater(window.navigator.userAgent)) {
            is_private = false;
            try {
                if (!window.indexedDB) {
                    is_private = true;
                }
            } catch (e) {
                is_private = true;
            }
        } else if (window.localStorage && /Safari/.test(window.navigator.userAgent)) {
            try {
                window.localStorage.setItem('test', 1);
            } catch(e) {
                is_private = true;
            }
            if (typeof is_private === 'undefined') {
                is_private = false;
                window.localStorage.removeItem('test');
            }
        }

        retry(
            function isDone() {
                return typeof is_private !== 'undefined' ? true : false;
            },
            function next(is_timeout) {
                callback(is_private);
            }
        );
    }

    detectPrivateMode(callback);

})(function (result) {
    console.log('[isInIncognito]: ' + result);
});