About Backbone.offline

Adds ability to store the data to localStorage and sync data with a server. It is useful when you want to:

• let your app to work offline in combination with cache manifest
• not to bootstrap initial data every time you save it to the localStorage. You can refresh your collection when you need and load initial data dramatically faster.
• create standalone HTML5 app which periodically syncs data to the server.

This library was extracted from project Saveidea

How to use

In order to start using Backbone.offline you need to add js/backbone.offline.js file to your project and add to initialize a line:

@storage = new Offline.Storage('dreams', this)

Now your collection will save and process data to localStorage. First param is a name of storage, second is a link to collection. This code does not break behavior of other collections. When a collection has no @storage attribute, commands will be delegated to Backbone.sync. Example of modified collection:

class Dreams extends Backbone.Collection
  url: '/api/dreams'

  initialize: ->
      @storage = new Offline.Storage('dreams', this)
  # your code ...

In order to work successfully with Backbone.offline, your app should follow for 3 simple rules:

• support default REST API on server
• models should have updated_at field
• models should have id primary key. If you use MongoDB you should change response replaced _id to id

How it works

Initially, the primary task for this library was to create web-app which can work standalone, therefore, initial requirements were as follows:

• full and incremental sync support;
• client’s local storage has own primary keys.

Backbone.offline replaces the module Backbone.sync to Offline.sync and does not add any additional logic to the app. At the same time, it does not add anything new to other Backbone modules.

Offline.Storage

Used for working with localStorage and based on a great library Backbone.localStorage. Offline.sync utilizes methods of class for all CRUD-operations.

It uses field sid in order to save server’s id. This field is used when request to server. When creating or changing data, model gets dirty attribute which initially equals true. The presence of this attribute is a signal for sync with a server, updated_at field changes too. This field is used for local comparison of versions with the server. Removed objects are added to special array of sid fields and they will be removed from sync with server.

@storage = new Offline.Storage('dreams', this, keys: {tag_id: @tags})

Optional parameter keys is used when your collection has a relation with other collections. In this example local tag_id will be changed to necessary primary key from @tags when sending data to the server.

Option autoPush allows to send request to the server on every save. It simply works like cache for your data.

@storage = new Offline.Storage('dreams', this, autoPush: true)

Offline.Sync

This is an algorithm for syncing local storage with a server. For inspiration was used Evernote EDAM algorithm, but later it has been changed significantly. The default behavior: synchronization of data with a server occurs on the collection change by using fetch(). If you want to sync data with the server more often, you can use an instance methods:

• full() — full collection reload
• incremental() — request data from the server with pull() and then send changed data to the server with push()
• push() - receive data from the server and merge with a current collection
• pull() - send dirty-data to the server with an atomic operations create, update, destroy. This ensures the reliability of stored data.

If you don't want to request data from server on fetch you can use option local: true: dreams.fetch(local: true)

Example:

dreams = new Dreams() # initialize collection
dreams.fetch() # GET /api/dreams

dreams.create(name: 'Visit Iceland') # add new dream to localStorage
dream = dreams.at(3)
dreams.save(name: 'Diving with scuba') # local save
dreams.sync.push() # POST /api/dreams and PUT /api/dreams/:id

Examples

Saveidea is a web-app for storing ideas, that appear in your mind during the day. It uses this library to work offline in the browser.

Change Log

• 0.2.0: Fixed bugs, added onLine() method, added autoPush option, upgrade to Backbone 0.9.2
• 0.1.1: First public release. Fixed bugs, added comments and documentation, refactoring
• 0.1.0: Library was extracted from project http://saveideanow.com

Special thanks

To Jerome Gravel-Niquet for backbone.localStorage and Jeremy Ashkenas for coffee-script and backbone.js

License

Licensed under MIT license. © 2012 Aleksey Kulikov, All Rights Reserved