mock-local-storage/lib/mock-localstorage.js

// Mock localStorage
'use strict';

(function () {

    function createStorage() {
        var s = {},
            noopCallback = function noopCallback() {},
            _itemInsertionCallback = noopCallback;

        Object.defineProperty(s, 'setItem', {
            get: function get() {
                return function (k, v) {
                    k = k + '';
                    if (!s.hasOwnProperty(k)) {
                        _itemInsertionCallback(s.length);
                    }
                    s[k] = v + '';
                };
            }
        });
        Object.defineProperty(s, 'getItem', {
            get: function get() {
                return function (k) {
                    k = k + '';
                    if (s.hasOwnProperty(k)) {
                        return s[k];
                    } else {
                        return null;
                    }
                };
            }
        });
        Object.defineProperty(s, 'removeItem', {
            get: function get() {
                return function (k) {
                    k = k + '';
                    if (s.hasOwnProperty(k)) {
                        delete s[k];
                    }
                };
            }
        });
        Object.defineProperty(s, 'clear', {
            get: function get() {
                return function () {
                    for (var k in s) {
                        if (s.hasOwnProperty(k)) {
                            delete s[k];
                        }
                    }
                };
            }
        });
        Object.defineProperty(s, 'length', {
            get: function get() {
                return Object.keys(s).length;
            }
        });
        Object.defineProperty(s, "key", {
            value: function value(k) {
                var key = Object.keys(s)[k];
                return !key ? null : key;
            }
        });
        Object.defineProperty(s, 'itemInsertionCallback', {
            get: function get() {
                return _itemInsertionCallback;
            },
            set: function set(v) {
                if (!v || typeof v != 'function') {
                    v = noopCallback;
                }
                _itemInsertionCallback = v;
            }
        });
        return s;
    }

    global.localStorage = createStorage();
    global.sessionStorage = createStorage();

    if (typeof window === 'undefined') {
        global.window = {};
    }

    window.localStorage = global.localStorage;
    window.sessionStorage = global.sessionStorage;
})();