Best client-side data store for iPhone web app?

I am building a web app targeting the iPhone. It is similar to a To Do list. I need the application to be able to work offline, i.e., it should allow the user to add/edit/delete entries when there is no connection to the server, which will later get synced when the server is online again.

How do you recommend I store this data (remember it is a web app) client-side ? I assume cookies are not safe to use, since they could be cleared at some point. I understand that both Dojo and ExtJs provide support for client-side data stores - which library will provide the best functionality while staying lean and mean? What other libraries should I investigate? Do any of these options provide synchronization capabilities with the server-side data store?

From stackoverflow

• Mobile Safari is WebKit based and is equipped with HTML5-based client-side database storage. See this Surfin' Safari blog post.

  If your web application is iPhone only, this is definitely the direction you should go.

  RedFilter : Wow, I love it! Thanks for pointing that out!

• Hi OrbMan, I have the same kind of issue. Do you any advice, suggestion (sample :)) for me?

  Thanks and have a good 1!