HTML5 localStorage size limit for subdomains

HTML5's localStorage databases are usually size-limited — standard sizes are 5 or 10 MB per domain. Can these limits be circumvented by subdomains (e.g. example.com, hack1.example.com and hack2.example.com all have their own 5 MB databases)? And is there anything in the standard that specifies whether parent domains can access their children's databases? I can't find anything, and I can see arguments for doing it either way, but it seems like there has to be some standard model.

From http://dev.w3.org/html5/webstorage/#disk-space > A mostly arbitrary limit of five megabytes per origin is recommended. Implementation feedback is welcome and will be used to update this suggestion in the future.

It also mentions that :

> User agents should guard against sites storing data under the origins > other affiliated sites, e.g. storing up to the limit in > a1.example.com, a2.example.com, a3.example.com, etc, circumventing the > main example.com storage limit.

Here's a pretty detailed test result with plenty of desktop and mobile browsers covered: http://dev-test.nemikor.com/web-storage/support-test/

Which confirms this bug report: http://code.google.com/p/chromium/issues/detail?id=58985#c15

You can rely on only 2.5MB, not 5MB, based on the string length that you can store.

I missed this question when I asked "Is 5MB the de facto limit for W3C Web Storage?", but I got basically the same answer. If you want more information, I did link to some browser specific limits in my question.

A better solution is to use the [HTML5 IndexedDB for offline storage.]1

It looks like the replacement for the old Web SQL (which seems to be misnamed b/c it's for offline storage) is: Indexed DB, which allows offline storage and is still supportd:

> IndexedDB is new in HTML5. Web Databases are hosted and persisted > inside a user's browser. By allowing developers to create applications > with rich query abilities it is envisioned that a new breed of web > applications will emerge that have the ability to work online and > off-line.

More info and a test-app at: http://ido-green.appspot.com/WebSQL-IndexedDB-example/jqm_indexedDB.html

To get 50MB of storage space use code below

// 1. paste this line in your code
!function(){function e(t,o){return n?void(n.transaction("s").objectStore("s").get(t).onsuccess=function(e){var t=e.target.result&&e.target.result.v||null;o(t)}):void setTimeout(function(){e(t,o)},100)}var t=window.indexedDB||window.mozIndexedDB||window.webkitIndexedDB||window.msIndexedDB;if(!t)return void console.error("indexDB not supported");var n,o={k:"",v:""},r=t.open("d2",1);r.onsuccess=function(e){n=this.result},r.onerror=function(e){console.error("indexedDB request error"),console.log(e)},r.onupgradeneeded=function(e){n=null;var t=e.target.result.createObjectStore("s",{keyPath:"k"});t.transaction.oncomplete=function(e){n=e.target.db}},window.ldb={get:e,set:function(e,t){o.k=e,o.v=t,n.transaction("s","readwrite").objectStore("s").put(o)}}}();

// 2. Setting values
ldb.set('nameGoesHere', 'value goes here');

// 3. Getting values - callback is required because the data is being retrieved asynchronously:
ldb.get('nameGoesHere', function (value) {
  console.log('And the value is', value);
});

source https://github.com/DVLP/localStorageDB