How persistent is localStorage?
I'm depending heavily on localStorage for a plugin I'm writing. All the user settings are stored in it. Some settings require the user the write regex'es and they would be sad if their regex rules are gone at some point. So now I am wondering just how persistent the localStorage is.
From the specs:
User agents should expire data from the local storage areas only for security reasons or when requested to do so by the user.
The above looks like it works just like cookies on the clientside. I.e. when the user clears all browser data (history, cookies, cache etc) the localStorage will also be truncated. Is this assumption correct?
Answer
Mozilla implements it like cookies:
DOM Storage can be cleared via "Tools -> Clear Recent History -> Cookies" when Time range is "Everything" (via nsICookieManager::removeAll)
https://developer.mozilla.org/en/DOM/Storage
In DOM Storage it is not possible to specify an expiration period for any of your data. All expiration rules are left up to the user. In the case of Mozilla, most of those rules are inherited from the Cookie-related expiration rules. Because of this you can probably expect most of your DOM Storage data to last at least for a meaningful amount of time.
Chrome implements it like cache:
LocalStorage is Not Secure Storage
HTML5 local storage saves data unencrypted in string form in the regular browser cache.
Persistence
On disk until deleted by user (delete cache) or by the app
https://developers.google.com/web-toolkit/doc/latest/DevGuideHtml5Storage
As for a "replacement for the Cookie", not entirely
Cookies and local storage really serve difference purposes. Cookies are primarily for reading server-side, LocalStorage can only be read client-side. So the question is, in your app, who needs this data — the client or the server?