Persistence (server synchronization) for knockout; sync with just about any data store.
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This is alpha software (full of bugs) and won't be live for a few more weeks

KnockoutSync is a persistence library that connects Knockout.js with a data layer.

When updates occur on the server, observed fields are automatically updated and knockout bindings are triggered. When knockout updates variables, they automatically update the server. Nested observable fields and records are handled with elegance.

This library does not use the mapping plugin; it's superfluous to the functionality provided here.


See some live examples here.

Sync observable to an existing record

    // loads recordXYZ and creates two-way sync
    var obs = ko.observable().extend({sync: store});'recordXYZ');

    // or in one step
    var obs = ko.observable().extend({sync: {store: store, key: 'recordXYZ'});

Create a new record and synchronize

    // creates record and establishes two-way sync
    var obs = ko.observable().extend({sync: store});
    obs({name: 'Rydia', email: 'summoner@ff2.tld'});

    // or in one step
    var obs = ko.observable({name: 'Rydia', email: 'i@remember.her'}).extend({sync: store}).create();

Sync observableArray to a list of records

    // loads records and start two-way sync
    var list = ko.observableArray().extend({sync: store});

Nested observables

   // creates record and starts two-way sync
   var nestedRec = ko.observable({
      name: ko.observable('Rei Ayanami'), // handled like any other field, synced if it changes
      email: 'i@heart.rei'
   }).extend({sync: store});

   // this also works and will not destroy the nested observable


Download the production version or the development version of knockout-sync.

In your web page, you need to have Knockout.js, and Knockout-sync. Underscore is optional, but makes things a bit more stable and performant.

   <script type="text/javascript" src="underscore.js"></script> <!-- optional -->
   <script type="text/javascript" src="knockout.js"></script>
   <script type="text/javascript" src="dist/knockout-sync.js"></script>


Create a Store (a connection to your database):

A Store is any place we can fetch data and hand it off to Knockout. Records are expected to have unique ids and the data store is assumed to have push capabilities, although these aren't strictly necessary.

You can find some example stores in the stores/ folder

    // create a Firebase Store
    var store = new ko.sync.stores.Firebase('', ['name', 'email'], {limit: 50});

Synchronizing observables

How we call sync depends on whether we are creating a new record or loading an existing one:

Synchronizing to an existing record:

// using the read method
var model = ko.observable().extend('sync', store);'recordXYZ');

// this is the same thing, but in one step
var model = ko.observable().extend('sync', {store: store, key: 'recordXYZ'});

Creating a new record:

// using the create method
var model = ko.observable().extend('sync', store);
model({name: 'Garet Jax', email: 'master@weapons.tld'});

// doing it in one step
var model = ko.observable({name: 'Garet Jax', email: 'master@weapons.tld'}).extend('sync', store); // automatically created!

Synchronizing observableArrays

Unlike observable, arrays are always synchronized as soon as they load. So there is no need to call read() to get the data locally.

// synchronized automatically
var list = ko.observableArray().extend('sync', store);

CRUD API for observable

Once an object is synced by calling .extend('sync', store), it has a crud member which can be used to perform standard CRUD operations:

    var model = ko.observable().extend('sync', store);

    // create a new record and sync
    model({name: 'Dr. Good', email: ''});
    model.crud.create(); // now we are synced

    // read a remote record and sync 'recordXYZ' );

    // update and sync
    model.crud.update( {name: 'Dr. Evil', email: ''} );

    // delete the record, we are no longer synced

    // crud actions automagically queue and run in sequence, so there
    // is never any need to worry about async ops running out of order! 'recordXYZ' ).update({name: 'Dr. Evil'}).delete()
        .ready.done(function() { /* no race conditions here */ });

CRUD API for observableArray

observableArray works almost exactly like observable. One notable difference is that an observableArray is immediately synchronized.

Note that there is no need to wrestle with destroy() and _destroy as deleted items are automagically tracked and handled internally!

    // sync an array with the Store and load all the records
    var users = ko.observableArray().extend({sync: store});; // valid, but does nothing because it has already been called

    // add a new record
    users.push({name: 'Lan Mandragoran', email: 'lord@seventowers.wot' });
    users.crud.create({name: 'Lan Mandragoran', emai: 'lord@seventowers.wot' }); // same thing

    // modify a record
    users.crud.update('record123', {name: 'Alf'}); // same thing, but using the key

    // delete a user from the list; also deletes from database
    users.splice(2, 1);
    users.crud.delete( 'recordXYZ' ); // same thing, but using the key

    // just like crud ops on observables, these can be chained too
    users.crud.update('record123', {name: 'Alf'}).delete( 'recordXYZ' ).create( {name: 'Lan Mandragoran', ...} )
        .ready.done(function() { /* all operations completed and saved */ });

Using Factory

Factory allows you to customize records and create nested observables.

You can make your records in observableArray, or any of their fields, into observable objects by passing a couple parameters into factory. This means that whenever they are updated, the data is automagically synchronized without the usual annoyance of having to find some way to trigger an update on observableArray (e.g. obsArray.replace or obsArray.splice).

   // configure Factory to make records observables
   var myFactory = new ko.sync.Factory(store, {observe: true});

   // configure Factory to make some fields observables
   var myFactory = new ko.sync.Factory(store, {observeFields: ['name']});

   // do both
   var myFactory = new ko.sync.Factory(store, {observe: true, observeFields: ['name']});

   // apply the factory to an array
   var list = ko.observableArray().extend({sync: {store: store, factory: myFactory}});

You can also create customized objects by building your own factory. Fret not; it's easier than you might think. This which allows you to specify everything about how new records get initialized.

   // create a factory
   var RecordFactory = ko.sync.Factory.extend({
      // optional constructor
      //init: function() {},

      // called every time a new row is received from the store
      make: function(key, data) {
         return {
            name: ko.observable(, // no problem here, it will get updated as you would hope
            computed: ko.computed() {...} // this will be left alone because it's not part of the store's fields
            key: key,

   var list = ko.observableArray().extend({sync: {
      store: store,
      factory: new RecordFactory();

   // update a nested field and sync to the Store, like magic!
   list()[0].name('Space Cadet Stimpy');

You don't need factories for observable objects, naturally. You can just declare your structure before calling read/create:

   var rec = ko.observable({ name: ko.observable(), email: ko.observable() }).extend({sync: {store: store, key: 'recordXYZ'}});

Missing Stuff (TODO)

  • sorting is left up to knockout logic and the Store to negotiate; assumes you'll transfer sort data with the records

Creating Your own Data Store

Read over src/classes/Store.js and implement each method according the purview of your particular needs and data storage device's capabilities.

Test the store by using the generac StoreTester. See test/testunit/TestStore.test.js (example) and test/lib/StoreTester.js (standard tests)

Please contribute stores/improvements back to the project!


Browse to test/index.html and enjoy the pretty colors (hopefully they are green)


Use the pull request feature in GitHub to contribute changes. Please provide or modify unit tests in test/testunit as needed