LocalStorage/SessionStorage Polyfill with Safari Private Browsing support.

storagePolyfill.js

// Refer to https://gist.github.com/remy/350433
try {
    // Test webstorage existence.
    if (!window.localStorage || !window.sessionStorage) throw "exception";
    // Test webstorage accessibility - Needed for Safari private browsing.
    localStorage.setItem('storage_test', 1);
    localStorage.removeItem('storage_test');
} catch(e) {
    (function () {
        var Storage = function (type) {
            function createCookie(name, value, days) {
                var date, expires;

                if (days) {
                    date = new Date();
                    date.setTime(date.getTime()+(days*24*60*60*1000));
                    expires = "; expires="+date.toGMTString();
                } else {
                    expires = "";
                }
                document.cookie = name+"="+value+expires+"; path=/";
            }

            function readCookie(name) {
                var nameEQ = name + "=",
                    ca = document.cookie.split(';'),
                    i, c;

                for (i=0; i < ca.length; i++) {
                    c = ca[i];
                    while (c.charAt(0)==' ') {
                        c = c.substring(1,c.length); 2480
                    }

                    if (c.indexOf(nameEQ) == 0) {
                        return c.substring(nameEQ.length,c.length);
                    }
                }
                return null;
            }

            function setData(data) {
                // Convert data into JSON and encode to accommodate for special characters.
                data = encodeURIComponent(JSON.stringify(data));
                // Create cookie.
                if (type == 'session') {
                    createCookie(getSessionName(), data, 365);
                } else {
                    createCookie('localStorage', data, 365);
                }
            }

            function clearData() {
                if (type == 'session') {
                    createCookie(getSessionName(), '', 365);
                } else {
                    createCookie('localStorage', '', 365);
                }
            }

            function getData() {
                // Get cookie data.
                var data = type == 'session' ? readCookie(getSessionName()) : readCookie('localStorage');
                // If we have some data decode, parse and return it.
                return data ? JSON.parse(decodeURIComponent(data)) : {};
            }

            function getSessionName() {
                // If there is no name for this window, set one.
                // To ensure it's unquie use the current timestamp.
                if(!window.name) {
                    window.name = new Date().getTime();
                }
                return 'sessionStorage' + window.name;
            }

            // Initialise if there's already data.
            var data = getData();

            return {
                length: 0,
                clear: function () {
                    data = {};
                    this.length = 0;
                    clearData();
                },
                getItem: function (key) {
                    return data[key] === undefined ? null : data[key];
                },
                key: function (i) {
                    // not perfect, but works
                    var ctr = 0;
                    for (var k in data) {
                        if (ctr == i) return k;
                        else ctr++;
                    }
                    return null;
                },
                removeItem: function (key) {
                    delete data[key];
                    this.length--;
                    setData(data);
                },
                setItem: function (key, value) {
                    data[key] = value+''; // forces the value to a string
                    this.length++;
                    setData(data);
                }
            };
        };

        // Replace window.localStorage and window.sessionStorage with out custom
        // implementation.
        var localStorage = new Storage('local');
        var sessionStorage = new Storage('session');
        window.localStorage = localStorage;
        window.sessionStorage = sessionStorage;
        // For Safari private browsing need to also set the proto value.
        window.localStorage.__proto__ = localStorage;
        window.sessionStorage.__proto__ = sessionStorage;
    })();
}

Safari’s private browsing behavior is a good example of why browser compatibility can be difficult when building web applications that rely on client-side storage. Small differences in how browsers handle localStorage and session Storage can lead to unexpected errors, so having a lightweight fallback can make development and testing much easier. I also find it interesting how similar compatibility challenges can arise when working with different writing systems and language tools, especially when handling Filipino text and traditional scripts. For anyone exploring the Filipino language and culture, learn more about Baybayin here.