InMemoryStorageLikeLocalStorage.js

/**
 * should behave like LocalStorage
 */
var inMemoryStorage = (function () {
    var items = {};

    return {
        length: 0, // todo: read only
        getItem: function (key) {
            return 'undefined' !== typeof items[key] ? items[key] : null;
        },
        setItem: function (key, value) {
            if ('undefined' === typeof items[key]) {
                // todo: handling values other than string
                items[key] = value;
                this.length++;
            }
        },
        deleteItem: function (key) {
            if ('undefined' !== typeof items[key]) {
                delete items[key];
                this.length--;
            }
        },
        key: function (index) {
            // todo
        },
        clear: function () {
            items = {};
            this.length = 0;
        }
    };
})();

inMemoryStorage.setItem('foo', 'bar'); // it works

inMemoryStorage['foo'] = 'bar'; // how do I get it to work?