The following links may help you to understand IndexedDB better:

HTML5 Storage Wars - localStorage vs. IndexedDB vs. Web SQL

http://csimms.botonomy.com/2011/05/html5-storage-wars-localstorage-vs-indexeddb-vs-web-sql.html

详解IndexedDB:

http://blackstone.blog.51cto.com/1282172/817757

Indexed Database API

http://www.w3.org/TR/IndexedDB/