juandopazo/gist:5405383

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    Storage

Motivation

There are 3 major types of storage is browsers up to date:

IndexedDB. The future.
localStorage. Limited in size and can be observed through the storage event.
WebSQL. Dropped by the W3C but it's still very present in the wild, with notable platforms like iOS and PhoneGap.


Green: IndexedDB; blue: WebSQL; yellow: localStorage
In the mobile world local cache and storage is very important for various reasons:

faster loading times
unreliable connections
offline use

My particular use case is an app to be used "in the field" where you probably don't have a connection and you need to do data entry. My solution is to save to a local storage and sync to the server when a connection is available. The 5 MB of localStorage may not be enough in my case, but I won't be able to tell until the app is used by real users.
Open questions


Is there enough interest in this considering the availability of localStorage?
Is it too early to use these technologies?

Architecture

The goal is to use conditional loading to load one of 3 or 4 sub-modules: indexeddb, websql, localstorage and a fallback to memory.

IndexedDB uses a key-based storage organized in "object stores".
WebSQL uses SQL tables. WebSQL can be used as a fallback for object stores by matching a table to a store and using tables with two columns: a key and a value column which saves the object serialized as JSON.
IndexedDB uses structured cloning which is similar to JSON.parse(JSON.stringify(obj)).

Open questions


Is falling back to localStorage a good idea considering the limited size and observability?
Is the whole concept OK or is it too hackish?
Should this include over-the-wire databases via some protocol?

API design

The API aims to find the lowest common denominator between all implementations. A database requires:

A name. Required by both IndexedDB and WebSQL
A version. Required by both IndexedDB and WebSQL
A structure, which means the name of each object store, tied to the version. Required by both IndexedDB and WebSQL
A size in bytes. Required by WebSQL

A Storage constructor receives all these parameters and creates an instance with properties with the names of each object store:
var storage = new Y.Storage({
  name: 'my database',
  version: 1,
  size: 5242880,
  stores: ['fooStore', 'barStore']
});

Assert.isObject(storage.fooStore); // true
Assert.isObject(storage.barStore); // true
A Storage instance also has a close method that closes the database connection/session.
A Store object is created for each requested store in a property of the same name. A store can perform the following actions:

get. Retrieve an object by key
put. Insert or update an object by key
remove. Remove an object by key
clear. Remove all objects from the store
count. Count the objects in the store

All methods return a promise.
Example:
storage.fooStore.put('some key', { foo: 'bar' }).then(...);
Open questions


Should Storage inherit from Base in order to use attributes for configuration and maybe fire close or error events? A versionchange event is very important.