JavaScript: The Definitive Guide, 6th Edition

Chapter 20. Client-Side Storage

Web applications can use browser APIs to store data locally on the user’s computer. This client-side storage serves to give the web browser a memory. Web apps can store user preferences, for example, or even store their complete state, so that they can resume exactly where you left off at the end of your last visit. Client-side storage is segregated by origin, so pages from one site can’t read the data stored by pages from another site. But two pages from the same site can share storage and can use it as a communication mechanism. Data input in a form on one page can be displayed in a table on another page, for example. Web applications can choose the lifetime of the data they store: data can be stored temporarily so that it is retained only until the window closes or the browser exits, or it can be saved to the hard drive and stored permanently, so that it is available months or years later.

There are a number of forms of client-side storage:

Web Storage

Web Storage is an API that was originally defined as part of HTML5 but was spun off as a standalone specification. That specification is still in draft form, but it is partially (and interoperably) implemented in all current browsers including IE8. This API consists of the localStorage and sessionStorage objects, which are essentially persistent associative arrays that map string keys to string values. Web Storage is very easy to use, is suitable for storing large (but not huge) amounts of data, and ...