HTML5 LocalStorage polyfill for IE7 using the userData behaviour

localstorage-userdata-polyfill.js

// if localStorage isn't available but IE's userData API is, polyfill it
// polyfill pattern based on https://gist.github.com/juliocesar/926500
if (Modernizr && !Modernizr.localstorage) {
    // set up storage element
    var storageNamespace = 'localStoragePolyfill',
        storage = document.createElement('div');
    if (typeof storage.addBehavior !== 'undefined') {
        storage.id = '_storage';
        storage.style.display = 'none';
        storage.style.behavior = 'url("#default#userData")';
        document.body.appendChild(storage);
        
        storage.load(storageNamespace);

        window.localStorage = {
            getItem     : function(id) { return storage.getAttribute(id) || undefined; },
            setItem     : function(id, val) { storage.setAttribute(id, val); storage.save(storageNamespace); },
            removeItem  : function(id) { storage.removeAttribute(id); storage.save(storageNamespace); },
            clear       : function() { return false; } // no way to appropriately polyfill this
        };
    }
}