storage.js

// Storage polyfill by Remy Sharp
// https://gist.github.com/350433
// Needed for IE7-

// Dependencies:
//  JSON (use json2.js if necessary)

// Tweaks by Joshua Bell (inexorabletash@gmail.com)
//  * URI-encode item keys
//  * Use String() for stringifying
//  * added length

if (!window.localStorage || !window.sessionStorage) (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);
                }

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

        function setData(data) {
            data = JSON.stringify(data);
            if (type == 'session') {
                window.name = data;
            } else {
                createCookie('localStorage', data, 365);
            }
        }

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

        function getData() {
            var data = type == 'session' ? window.name : readCookie('localStorage');
            return data ? JSON.parse(data) : {};
        }


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

        function numKeys() {
            var n = 0;
            for (var k in data) {
                if (data.hasOwnProperty(k)) {
                    n += 1;
                }
            }
            return n;
        }

        return {
            clear: function() {
                data = {};
                clearData();
                this.length = numKeys();
            },
            getItem: function(key) {
                key = encodeURIComponent(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 decodeURIComponent(k);
                    else ctr++;
                }
                return null;
            },
            removeItem: function(key) {
                key = encodeURIComponent(key);
                delete data[key];
                setData(data);
                this.length = numKeys();
            },
            setItem: function(key, value) {
                key = encodeURIComponent(key);
                data[key] = String(value);
                setData(data);
                this.length = numKeys();
            },
            length: 0
        };
    };

    if (!window.localStorage) window.localStorage = new Storage('local');
    if (!window.sessionStorage) window.sessionStorage = new Storage('session');

})();