While building a Google Reader client using jQuery Mobile, and Lawnchair using just localStorage became problematic. No matter the browse they all had a hard 5MB cap, and it wouldn’t grow. 5MB is roughly equivalent to 1600 google reader articles stored as JSON. At any given time a google reader client should be able to store 20,000 to 50,000 stories.
Using localStorage for what some have called a local cookie, is probably a good idea, but it is not meant as a general purpose database.
Right now the only other options for client side storage is WebSQL. WebSQL is on it’s way out, it’s going to be replaced by IndexedDB, but who knows when. This has lead to limited support for WebSQL. This narrowed the browsers on which the Google Reader client could run. Ultimately this was going to be a test for PhoneGap, so mostly WebKit Browsers. The iPhone, and Android, and Palm versions of webkit have WebSQL. Then there is Blackberry, which has some form of Blackberry storage API for which Lawnchair has an adapter for.
Using the WebSQL adaptor for lawnChair was an easy cut-over. There are less storage limits when using WebSQL then when using localStorage. Storing a months worth of unread articles was not a problem. On a side note, dates in JS have always been lacking a great API. Though, there is Datejs. It’s old, and marketed as a fuzzy date parser, but it has a wonderful API for picking dates. For example:
var pastDate = Date.now().add(-7).days();