The Web Storage API described in localStorage and sessionStorage can be thought of as a particularly simple kind of database that persists simple key/value pairs. But in addition, there are two client-side database APIs that are “real” databases. One, known as Web SQL Database, is a simple relational database that supports basic SQL queries. Chrome, Safari, and Opera implemented this API, but Firefox and IE have not, and likely never will. Work on the official specification of this API has stopped and this full-featured SQL database will probably never become an official standard nor an unofficial but interoperable feature of the web platform.
Standardization efforts are now focused on another database API, known as IndexedDB. It is too early to document this API in any detail (it is not covered in Part IV), but Firefox 4 and Chrome 11 include implementations, and this section includes a working example that demonstrates some of the most important features of the IndexedDB API.
IndexedDB is an object database, not a relational database, and it is much simpler ...