If you want to keep track programmatically of when the storage area changes, you can trap the storage event. The storage event is fired on the window object whenever setItem(), removeItem(), or clear() is called and actually changes something. For example, if you set an item to its existing value or call clear() when there are no named keys, the storage event will not fire, because nothing actually changed in the storage area.
The storage event is supported everywhere the localStorage object is supported, which includes Internet Explorer 8. IE 8 does not support the W3C standard addEventListener (although that will finally be added in IE 9). Therefore, to hook the storage event, you’ll need to check which event mechanism the browser supports. (If you’ve done this before with other events, you can skip to the end of this section. Trapping the storage event works the same as every other event you’ve ever trapped. If you prefer to use jQuery or some other JavaScript library to register your event handlers, you can do that with the storage event, too.)
While the past is littered with hacks and workarounds, the present condition of HTML5 Storage is surprisingly rosy. A new API has been standardized and implemented across all major browsers, platforms, and devices. As a web developer, that’s just not something you see every day, is it? But there is more to life than “5 megabytes of named key/value pairs,” and the future of persistent local storage is… how shall I put it… well, there are competing visions.
One vision is an acronym that you probably know already: SQL. In 2007, Google launched Gears, an open source cross-browser plugin which included an embedded database based on SQLite. This early prototype later influenced the creation of the Web SQL Database specification. Web SQL Database (formerly known as “WebDB”) provides a thin wrapper around a SQL database, allowing you to do things like this from JavaScript: