A feature-filled and friendly way to take advantage of localStorage and sessionStorage (JSON, namespacing, extensions, etc).

Download: store2.min.js or store2.js
NPM: npm install store2
Bower: bower install store2
NuGet: Install-Package store2

The main store function can handle set, get, transact, setAll, getAll and clear actions directly. Respectively, these are called like so:

store(key, data);                 // sets stringified data under key
store(key);                       // gets and parses data stored under key
store(key, fn[, alt]);            // run transaction function on/with data stored under key
store({key: data, key2: data2});  // sets all key/data pairs in the object
store();                          // gets all stored key/data pairs as an object
store(false);                     // clears all items from storage

There are also more explicit and versatile functions available:

store.set(key, data[, overwrite]); // === store(key, data);
store.setAll(data[, overwrite]);   // === store({key: data, key2: data});
store.get(key[, alt]);             // === store(key);
store.getAll();                    // === store();
store.transact(key, fn[, alt]);    // === store(key, fn[, alt]);
store.clear();                     // === store(false);
store.has(key);                    // returns true or false
store.remove(key);                 // removes key and its data
store.each(callback);              // called with key and data args, return false to exit early
store.keys();                      // returns array of keys
store.size();                      // number of keys, not length of data
store.clearAll();                  // clears *ALL* areas (but still namespace sensitive)

Passing in false for the optional overwrite parameters will cause set actions to be skipped if the storage already has a value for that key. All set action methods return the previous value for that key, by default. If overwrite is false and there is a previous value, the unused new value will be returned.

Functions passed to transact will receive the current value for that key as an argument or a passed alternate if there is none. When the passed function is completed, transact will save the returned value under the specified key. If the function returns undefined, the original value will be saved. This makes it easy for transact functions to change internal properties in a persistent way:

store.transact(key, function(obj) {
    obj.changed = 'newValue';// this change will be persisted
});

All of these use the browser's localStorage (aka "local"). Using sessionStorage merely requires calling the same functions on store.session:

store.session("addMeTo", "sessionStorage");
store.local({lots: 'of', data: 'altogether'});// store.local === store :)

All the specific get, set, etc. functions are available on both store.session and store.local, as well as any other storage facility registered via store.area(name, customStorageObject) by an extension, where customStorageObject must implement the Storage interface. This is how store.old.js extends store.js to support older versions of IE and Firefox.

If you want to put stored data from different pages or areas of your site into separate namespaces, the store.namespace(ns) function is your friend:

var cart = store.namespace('cart');
cart('total', 23.25);// stores in localStorage as 'cart.total'
console.log(store('cart.total') == cart('total'));// logs true
console.log(store.cart.getAll());// logs {total: 23.25}
cart.session('group', 'toys');// stores in sessionStorage as 'cart.group'

The namespace provides the same exact API as store but silently adds/removes the namespace prefix as needed. It also makes the namespaced API accessible directly via store[namespace] (e.g. store.cart) as long as it does not conflict with an existing part of the store API.

The 'namespace' function is one of two "extra" functions that are also part of the "store API":

store.namespace(prefix[, noSession]);// returns a new store API that prefixes all key-based functions
store.isFake();// is this storage persistent? (e.g. is this old IE?) 

If localStorage or sessionStorage are unavailable, they will be faked to prevent errors, but data stored will NOT persist beyond the life of the current document/page. Use the store.old.js extension to add persistent backing for the store API in ancient browsers.

These mostly could use further documentation and abuse...er...testing. Contributions are welcome! In particular, any ES6 user interested in making these importable in ES6 would be appreciated.

• store.old.js - Add working localStorage and sessionStorage polyfills for ancient browsers
• store.overflow.js - Fall back to fake storage on quota errors (e.g. very useful for Safari private mode)
• store.cache.js - To make data expire, pass a number of seconds as the overwrite (third) param on set() calls
• store.on.js - Superior storage event handling (per key, per namespace, etc in IE9+)
• store.array.js - Easy, powerful array functions for any and all data (e.g. store.push(key, v1, v2)).
• store.dom.js - Declarative, persistent DOM element content via store.

• store.quota.js - Register callbacks to handle (and even cancel) quota errors
• store.measure.js - Experimental extension for measuring space used and available (needs work)
• store.onlyreal.js - When only fake storage is available, silently fail instead of faking it.
• store.dot.js - Creates accessors for keys (e.g. store.foo == store.get('foo'))
• store.deep.js - Allow retrieval of properties from within stored objects (e.g. store.get('key.property'))

• 2010-02-10 v0.1 (extraction from esha.js)
• 2010-05-25 v1.0 (internal release)
• 2013-04-09 v2.0.3 (public) - First GitHub release
• 2013-04-20 v2.1.0 (public) - Drops flawed/confusing/unused key(i) method, fixes extension problems.
• 2013-04-30 v2.1.1 (public) - Browserify (and friends) support (module.exports = store)
• 2013-05-30 v2.1.2 (public) - Component support (old component.json is now bower.json)
• 2013-09-08 v2.1.3 (public) - Remove unnecessary component.js shim
• 2014-03-01 v2.1.4 (public) - Package definition and store.overflow.js updates
• 2014-03-06 v2.1.5 (public) - AMD support and Component improvements
• 2014-03-10 v2.1.6 (public) - Fix AMD support flaw
• 2015-02-02 v2.2.0 (public) - Change store.cache.js to use seconds, not minutes.
• 2015-05-05 v2.2.1 (public) - node.js compatibility
• 2015-05-08 v2.2.2 (public) - Always expose global to allow extensions to always work.
• 2015-05-22 v2.3.0 (public) - Use fake storage for Safari private mode (instead of letting quota exceptions go)
• 2015-10-27 v2.3.2 (public) - Add source map
• 2017-01-04 v2.4.0 (public) - Add store.transact(key, fn[, alt])
• 2017-01-09 v2.5.0 (public) - Update for issue #34; new extensions (array, dot, and deep); only expose global in non-AMD/CommonJS environments (PR #35)
• 2017-03-28 v2.5.1 (public) - Lint fixes, dependency updates
• 2017-08-09 v2.5.2 (public) - Fix clear() in fake storage (thx to Martin Kluska)

When i went to publish this on NPM i discovered another store.js by Marcus Westin. To my surprise, even our APIs had notable overlap. His has fewer features and includes superior support for IE 6/7 in the main lib. I contacted him with the idea of merging the featuresets, but we agreed it wouldn't work. He saw his library as a temporary polyfill meant to fade away with IE 6/7. This project is meant to always be useful, as a better way to use localStorage, with polyfilling as an extension. I do hope to incorporate IE 6/7 improvements from the other store.js into store.old.js at some point, but it is not a priority.

To minimize confusion, i will be publishing the library as 'store2', but the main function will always be store. My apologies for the confusion caused while i was publishing this as another 'store'.