index.js

(function() {
  'use strict';
  try {
    // Test webstorage existence.
    if (!window.localStorage || !window.sessionStorage) throw "exception";
    // Test webstorage accessibility - Needed for Safari private browsing.
    window.localStorage.setItem('storage_test', 1);
    window.localStorage.removeItem('storage_test');
  } catch (e) {
    (function() {
      function createCookie(name, value, days) {
        var expires;
        if (days) {
          var date = new Date();
          date.setTime(date.getTime() + (days * 24 * 60 * 60 * 1000));
          expires = "; expires=" + date.toGMTString();
        } else {
          expires = "";
        }
        document.cookie = encodeURIComponent(name) + "=" + encodeURIComponent(value) + expires + "; path=/";
      }

      function readCookie(name) {
        var results = document.cookie.match('(^|;) ?'+encodeURIComponent(name)+'=([^;]*)(;|$)');
        return results ? decodeURIComponent(results[2]) : null;
      }

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

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

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

        function getSessionName() {
          if (!window.name) {
            window.name = Math.random()+'-'+(new Date().getTime());
          }
          return 'sessionStorage-' + window.name;
        }

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

        var obj = {
          POLYFILLED: true,
          length: 0,
          clear: function() {
            data = {};
            this.length = 0;
            clearData();
          },
          getItem: function(key) {
            return Object.prototype.hasOwnProperty.call(data, key) ? data[key] : null;
          },
          key: function(i) {
            var ctr = 0;
            for (var k in data) {
              if (ctr++ == i)
                return k;
            }
            return null;
          },
          removeItem: function(key) {
            if (Object.prototype.hasOwnProperty.call(data, key)) {
              delete data[key];
              this.length--;
              setData(data);
            }
          },
          setItem: function(key, value) {
            if (!Object.prototype.hasOwnProperty.call(data, key)) {
              this.length++;
            }
            data[key] = ''+value;
            setData(data);
          }
        };
        return obj;
      }

      var localStorage = new Storage('local');
      var sessionStorage = new Storage('session');
      try {
        window.localStorage = localStorage;
        window.sessionStorage = sessionStorage;
      } catch(e) {}
      try {
        // For Safari private browsing need to also set the proto value.
        window.localStorage.__proto__ = localStorage;
        window.sessionStorage.__proto__ = sessionStorage;
      } catch(e) {}
    })();
  }
})();