When is localStorage cleared?

How long can I expect data to be kept in localStorage. How long will an average user's localStorage data persist? If the user doesn't clear it, will it last till a browser re-install?

Is this consistent across browsers?

localStorage is also known as Web Storage, HTML5 Storage, and DOM Storage (these all mean the same thing).

localStorage is similar to sessionStorage, except that data stored in localStorage has no expiration time, while data stored in sessionStorage gets cleared when the browsing session ends (i.e. when the browser / browser tab is closed). Session storage is used much less often than localStorage, and exists only within the current browser tab - even two tabs loaded with the same website will have different sessionStorage data. sessionStorage data survives page refresh, but not closing/opening the tab. LocalStorage data, on the other hand, is shared between all tabs and windows from the same origin. LocalStorage data does not expire; it remains after the browser is restarted and even after OS reboot. Source

localStorage is available on all browsers, but persistence is not consistently implemented. In particular, localStorage can be cleared by user action and may be cleared inadvertently (who would think that clearing all cookies also clears localStorage?).

In Firefox, localStorage is cleared when these three conditions are met: (a) user clears recent history, (b) cookies are selected to be cleared, (c) time range is "Everything"

In Chrome, localStorage is cleared when these conditions are met: (a) clear browsing data, (b) "cookies and other site data" is selected, (c) timeframe is "from beginning of time". In Chrome, it is also now possible to delete localStorage for one specific site.

In IE, to clear localStorage: (a) Tools--Internet Options, (b) General tab, (c) delete browsing history on exit, (d) ensure "Cookies and website data" (or "temporary internet files and website files") is selected, (e) consider unchecking "Preserve Favorites website data" at the top

In Safari: (a) Click Safari (b) Preferences (c) Select the Privacy tab (d) Click Remove all website data (e) Click Remove Now

Opera: Despite excellent articles on localStorage from the Opera site, I haven't yet found clear (non-programmatic) instructions to users on how to clear localStorage. If anyone finds, please leave a comment below this answer with reference link.

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The Opera dev site has an excellent summary of localStorage:

> The current way of storing data on the client-side — cookies — is a > problem: > > * Low size: Cookies generally have a maximum size of around 4 KB, which > is not much good for storing any kind of complex data > > * It’s difficult for cookies to keep track of two or more transactions on the same > site, which might be happening in two or more different tabs > > * Cookies > can be exploited using techniques such as cross site scripting, > resulting in security breaches > > Other (less popular) alternatives to > cookies include techniques involving query strings, hidden form > fields, flash based local shared objects, etc. Each with their own set > of problems related to security, ease of use, size restrictions etc. > So up until now we have been using pretty bad ways of storing data on > the user’s end. We need a better way, which is where Web Storage comes > in. > > Web Storage > > The W3C Web Storage specification was designed as a better way of > storing data on the client-side. It has two different types of > storage: Session Storage and Local Storage. > > Both Session and Local Storage will typically be able to store around > 5 MB of data per domain, which is significantly more than cookies.

Resources:

https://developer.mozilla.org/en-US/docs/Web/API/Window/sessionStorage

https://javascript.info/localstorage

https://dev.opera.com/articles/web-storage/

http://www.quirksmode.org/html5/storage.html

http://www.ghacks.net/2015/02/05/how-to-clear-web-storage-in-your-browser-of-choice/

https://nakedsecurity.sophos.com/2014/11/05/how-to-clear-out-cookies-flash-cookies-and-local-storage/

http://www.opera.com/dragonfly/documentation/storage/

DOMStorage article on MDN (written by John Resig)

http://ejohn.org/blog/dom-storage/

W3C draft says this

> User agents should expire data from the local storage areas only for security reasons or when requested to do so by the user. User agents should always avoid deleting data while a script that could access that data is running.

So if browsers follow the spec it should persist untill the user removes it on all browsers, I have not found any that have deleted on any off my projects.

A good article to read is also http://ejohn.org/blog/dom-storage/

Duration

Unlimited. The data persists through browser & OS restarts.

Capacity

Each domain can store minimum of 5MB of data in LocalStorage.

For some browsers you can store up to 1GB of data.

In Chrome while performing 'clear browsing data' , if you choose 'Cookies and other site and plugin data' option then sessionStorage data will be erased.

The content in localstorage is persistent as long as the user chooses to clear the storage (entirely or a single value inside it)

About the consistency across browser, localstorage is currently available on every major browser, including IE8+ (see http://caniuse.com/#feat=namevalue-storage)