HTML5 Local storage vs. Session storage

Few other points which might be helpful to understand differences between local and session storage

1. Both local storage and session storage are scoped to document origin, so

   https://mydomain.example/ 
   http://mydomain.example/
   https://mydomain.example:8080/
   

   All of the above URL's will not share the same storage. (Notice path of the web page does not affect the web storage)

2. Session storage is different even for the document with same origin policy open in different tabs, so same web page open in two different tabs cannot share the same session storage.

3. Both local and session storage are also scoped by browser vendors. So storage data saved by IE cannot be read by Chrome or FF.

The only difference is that localStorage has a different expiration time, sessionStorage will only be accessible while and by the window that created it is open.
localStorage lasts until you delete it or the user deletes it.
Lets say that you wanted to save a login username and password you would want to use sessionStorageover localStorage for security reasons (ie. another person accessing their account at a later time).
But if you wanted to save a user's settings on their machine you would probably want localStorage. All in all:

localStorage - use for long term use.
sessionStorage - use when you need to store somthing that changes or somthing temporary

localStorage and sessionStorage both extend Storage. There is no difference between them except for the intended "non-persistence" of sessionStorage.

That is, the data stored in localStorage persists until explicitly deleted. Changes made are saved and available for all current and future visits to the site.

For sessionStorage, changes are only available per tab. Changes made are saved and available for the current page in that tab until it is closed. Once it is closed, the stored data is deleted.