Detecting If a Browser Is Using Private Browsing Mode

    var fs = window.RequestFileSystem || window.webkitRequestFileSystem;
    if (!fs) {
      console.log("check failed?");
    } else {
      fs(window.TEMPORARY,
         100,
         console.log.bind(console, "not in incognito mode"),
         console.log.bind(console, "incognito mode"));
    }

Private / Incognito Mode Detection for iOS 12 Safari

Chrome Devtools => The module to detect incognito/private mode is called "detect-private-browsing" located at webpack:///./~/detect-private-browsing/index.js

// ./~/detect-private-browsing/index.js

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) >= 10) {
        return true;
    }
    // MS Edge Detection from this gist: https://gist.github.com/cou929/7973956
    var edge = /edge/.exec(ua); 
    if (edge && edge[0] == "edge") { 
        return true; 
    }
    return false;
}

module.exports = {
    detectPrivateMode: function(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)) {

            // One-off check for weird sports 2.0 polyfill
            // This also impacts iOS Firefox and Chrome (newer versions), apparently
            // @see bglobe-js/containers/App.js:116
            if (window.safariIncognito) {
                is_private = true;
            } else {
                        try {
                           window.openDatabase(null, null, null, null);
                        } catch (e) {
                           is_private = true;
                        }

                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);
            }
        );
    }
};

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