Getting Started

What it is

var User = Nested.Model.extend({
    urlRoot : '/api/users',

    defaults : {
        // Primitive types
        login    : "", // String
        email    : String.value( null ), // null, but String
        loginCount : Number.has.toJSON( false ) // 0, not serialized
        active   : Boolean.value( true ), // true

        created  : Date, // new Date()

        settings : Settings, // new Settings()

        // collection of models, received as an array of model ids
        roles    : Role.Collection.subsetOf( rolesCollection ),
        // reference to model, received as model id.
        office   : Office.from( officeCollection )

var collection = new User.Collection();
collection.fetch().done( function(){
    var user = collection.first();
    console.log( ); // native properties
    console.log( );
    console.log( user.roles.first().name );

Types are being checked in run-time on assignment, but instead of throwing exceptions it tries to cast values to defined types.

    user.login = 1;
    console.assert( user.login === "1" ); = undefined;
    console.assert( === false );

    user.loginCount = "hjkhjkhfjkhjkfd";
    console.assert( _.isNan( user.loginCount ) );

    user.settings = { timeZone : 180 }; // same as user.settings.set({ timeZone : 180 })
    console.assert( user.settings instanceof Settings );

Master Build Status Develop Build Status

NestedTypes is state-of-the-art backbonejs-compatible model framework.

Complex attribute types

It’s achieved using attribute type annotations, which feels in much like statically typed programming language. Yet, this annotations are vanilla JavaScript, no transpiler step is required.


NestedTypes check types on every model update and perform dynamic type casts to ensure that attributes will always hold values of proper type.

As result, NestedTypes models are extremely reliable. It’s impossible to break client-server protocol with inaccurate attribute assignment. If something will go really wrong, it will warn you with a messages in the console.


NestedTypes uses attribute type information for sophisticated optimizations targeting modern JS JIT engines.

Compared to backbonejs, model updates are about 30 times faster in Chrome/nodejs, and 4 times faster in other browsers.

Easy to use and learn

NestedTypes was originally designed with an idea to make backbonejs more friendly for newbiews.

What we do, is taking intuitive newbie approach to backbonejs, and turn it from the mistake to legal way of doing things.

Installation & Requirements

CommonJS (node.js, browserify):

var Nested = require( 'nestedtypes' );

CommonJS/AMD (RequireJS). ‘backbone’ and 'underscore’ modules must be defined in config paths.

require([ 'nestedtypes' ], function( Nested ){ ... });

Browser’s script tag

<script src="underscore.js" type="text/javascript"></script>
<script src="backbone.js" type="text/javascript"></script>
<script src="nestedtypes.js" type="text/javascript"></script>
<script> var Model = Nested.Model; ... </script>

Supported JS environments

NestedTypes requires modern JS environment with support for native properties. It’s tested in IE 9+, Chrome, Safari, Firefox, which currently gives you about 95% of all browsers being used for accessing the web.

node.js and io.js are also supported.

Packaging and dependencies

NestedTypes itself is packaged as UMD (Universal Module Definition) module, and should load dependencies properly in any environment.

NestedTypes require underscore and backbone libraries. They either must be included globally with <script>tag or, if CommonJS/AMD loaders are used, be accessible by their standard module names.


bower install backbone.nested-types


npm install backbone.nested-types


Copy nestedtypes.js file to desired location.



NestedTypes core functionality relies on improved Object.extend function, which is also available as separate module without any side dependencies. It compatible with Backbone’s extend, while providing some additional capabilities important for NestedTypes and its applications, such as:

You can attach it to your Constructor function like this:

Object.extend.attach( MyConstructor1, MyConstructor2, ... );

Object.extend can also be used directly to create classes.

When used as a part of NestedTypes, all Object.extend classes also implements Backbone.Events, thus your custom objects are capable of sending and receiving backbone events.

You can add your own methods to all classes like this:

Object.extend.Class.prototype.myMethod = function(){...}

Defining classes

var MyClass = Object.extend({
    a : 1,
    inc : function(){ return this.a++; },

    initialize : function( x ){
        this.a = x;
    factory : function( x ){
        return new MyClass( x );

When executed directly, Object.extend( protoProps, staticProps ) creates constructor function and extends its prototype with protoProps properties, also attaching staticProps to the constructor itself. Constructor will call optional initialize method.


var Subclass = MyClass.extend({
    b : 2,
    initialize : function( a, b ){
        Subclass.__super__.initialize.apply( this, arguments );
        this.b = b;

Every constructor created with Object.extend may be further extended with extend method. Correct prototype chain will be built and attached to subclass constructor. Every subclass constructor has __super__ property pointing to the prototype of the base class.

Overriding constructor

var Subclass = MyClass.extend({
    b : 2,
    constructor : function( a, b ){
        MyClass.apply( this, arguments );
        this.b = b;

You may override constructor instead of dealing with initialize function.

Native Properties

var Class = Object.extend({
    properties: {
        readOnly : function(){ return 'hello!'; },
        readWrite : {
            get : function(){ return this._value2; },
            set : function( value ){
                this._value2 = value;

Native properties can be defined with properties spec. For read-only properties, it’s enough to supply get function as spec. Otherwise, properties specs format is the same as accepted by standard Object.defineProperties function.

You can access native properties as if it would be regular object member variable.

var x = c.readOnly

c.readWrite = 1;

Forward declarations

var A = Object.extend(),
    B = Object.extend( function(){ this.b = 'b'; } );

    bType : B

    aType : A

Classes can be created with an Object.extend(), and defined later using MyClass.define( protoProps, staticProps ) function. It can be helpful to resolve circular dependencies.

define cannot be used to override constructor. It can be achieved by passing constructor function to extend, as it is done for B in the example.

Console Warnings

var A = Object.extend({
    a :  function(){}

var B = A.extend({
    a : 0 // Warning about type error

If you try to override base class function with non-function value, Object.extend will notify you about that with a warning to the console. Cause usually it’s a mistake.

In this case, you’ll see in the console following message:

[Type Warning] Base class method overriden with value in Object.extend({ a : 0 }); Object = >...

function warning( Ctor, name, value ){
    throw new TypeError( 'Whoops...' );

Object.extend.error.overrideMethodWithValue = warning;

You may override default warning handling assigning our own function to Object.extend.error.overrideMethodWithValue.



In NestedTypes model definition’s defaults section is the specification of model’s attributes. attributes keyword may be used instead of defaults.

In defaults or attributes, you may specify attribute default value, its type, and different options of attribute behavior. Refer to corresponding sections of the manual for details.

In NestedTypes, attribute declaration is mandatory. When you try to set an attribute which doesn’t have default value, you’ll got an error in the console.

model.defaults( [ attrs ], [ options ] )

    var UserInfo = Nested.Model.extend({
        defaults : {
            name : 'test'

    var DetailedUserInfo = UserInfo.extend({
        attributes : { // <- alternative syntax for 'defaults'
            login : '',
            roles : [ 'user' ]

    var user = new DetailedUserInfo();

In Backbone, ‘name’ attr is not inherited and would be undefined. In NestedTypes it’s inherited, and you can access it directly.

    console.assert( === 'test' ); = 'admin';

In Backbone all models will share the same instance of [ 'user’ ] array. Bug. In NestedTypes, user.roles is deep copied on creation. Good practice.

    user.roles.push( 'admin' );

NestedTypes automatically creates defaults function for every model from model attribute’s spec. Base model attributes will be inherited.

Following statement can be used to return every model to its original state:

model.set( model.defaults() )

defaults function accepts optional attrs argument with attribute values hash and fills missing attributes with default values.

default values deep cloning

When new model is being created, NestedTypes will deep clone all items (including objects and arrays) from defaults object.

Correct defaults inheritance

When extending some existing model definition, NestedTypes will property merge base model’s defaults.


NestedTypes creates native property for every attribute.

model.attr = val; has the same effect as model.set( 'attr', val );

val = model.attr; has the same effect as val = model.get( 'attr' );

You still might need to use model.set in cases when you want to set multiple attributes at once, or to pass some options.

In NestedTypes, is assignable property, linked to model.attributes[ model.idAttribute ]. = 5 has the same effect as model.set( model.idAttribute, 5 )

var M = Nested.Model.extend({
    defaults : {
        a : 1

    properties : {
        b : function(){ return this.a + 1; }

var m = new M();
console.log( m.b ); // 2

Custom native properties specification. Most typical use case is calculated properties. is the part of Object.extend functionality. Refer to Object.extend manual section for details.


Set model attributes. In NestedTypes, this operation is type safe. It’s guaranteed that model attribute will always hold null or value of specified type.

  1. Values are converted to proper types. For existing nested models and collections deep update may be invoked. Refer to Attribute Types manual section for details.
  2. Set hooks are being executed for changing attributes. Refer to Attribute Options section for details.
  3. Events are being registered for changing attributes. replace:attr events are fired,
  4. Attribute values are being set, firing regular change events.

On attempt to set an attribute which is not defined, warning message will be printed to console.

In NestedTypes, you can assign individual model attributes directly, and it’s faster than using set: model.attr = val;

model.get( 'attr’ )

Get attribute value by name. Returned value can be modified with get hook in attribute definition.

In NestedTypes, you can access model attributes directly, and it’s faster than get: val = model.attr;

Deep clone

model.deepClone() or model.clone({ deep : true })

Deeply clone model with all nested models, collections, and other complex types.

Deep get and set

x = model.deepGet( 'attr1.attr2.modelId.attr3.objId' )

Get attribute by dot-separated path. Model attribute name, or model.cid (for collection attribute), index (for array), or object property name ( for plain objects) may be used as an elements of the path.

If some model in the middle of path doesn’t exists, it will return undefined.

x = model.deepSet( 'attr1.attr2.modelId.attr3.objId', x )

Set model value by dot-separated path. If model attribute in the middle of path equals to null, empty model will be created.


var UserInfo = Nested.Model.extend({
    urlBase : '/api/user/',

    defaults : {
        login : '',
        roles : [ 'user' ]

    collection : {
        initialize : function(){

var collection = new UserInfo.Collection();

Every model definition has its own correct Collection type extending base Model.Collection, which can be accessed instantly without declaration. Collection.model and Collection.url properties are taken from model.

var collection = new AnyModel.Collection();

You could customize collection definition providing the spec in Model.collection, which then will be passed to BaseModel.Collection.extend.


var Tree = Nested.Mode.extend();

    defaults : {
        branches : Tree.Collection

Forward declarations makes possible type-accurate recursive and mutually recursive model definitions.

Model.define is the part of Object.extend functionality. Refer to Object.extend manual section for details.



var M = Nested.Model.extend({
    defaults : {
        // Attribute-level toJSON.
        a : String.has.toJSON( false ),
        b : 5

    // Model-level toJSON.
    toJSON : function(){
        // Call NestedTypes serialization algorithm.
        var json = Nested.Model.prototype.toJSON.apply( this, arguments );

        // Do some json transformations...

        return json;

All nested attributes will be serialized automatically.

You can control serialization of any attribute with toJSON attribute option. Most typical use case is to exclude attribute from those which are being sent to the server.


var M = Nested.Model.extend({
    defaults : {
        // Attribute-level parse transform.
        a : AbstractModel.has.parse( AbstractModel.factory )

    // Model-level parse transform.
    parse : function( resp ){
        // Do some resp transformations...

        // (!) Call attribute-level parse transform (!)
        return this._parse( resp );

All nested attributes will be parsed automatically.

You can customize parsing of any attribute with parse attribute option. Most typical use case is to create proper model subclass for abstract model attribute.

You may need to override model-level parse function in order to change attribute names or top-level format.

Attribute Types

Generic Constructor types

var A = Nested.Model.extend({
    defaults : {
        obj1 : Ctor, // = new Ctor()
        obj2 : Ctor.value( null ), // = null
        obj3 : Ctor.value( something ), // = new Ctor( something )

var a = A();

a.obj2 = "dsds"; // a.obj2 = new Ctor( "dsds" );

console.assert( a.obj2 instanceof Ctor );

Type spec format

Type specs may be used instead of init values in Model.defaults. They looks like this:

name : Constructor or name : Constructor.value( x )

where Constructor is JS constructor function, and x is null or value passed as constructor’s argument.

When value is not given, typed attribute is initialized invoking new Constructor().

Type casting rules

When typed attribute is assigned with the value…


Constructor types are being serialized with JSON.stringify() method. You may override toJSON for your type to customize serialization. I.e.

will be invoked to produce JSON, if this method exists.

When receiving data from server, standard type cast logic is used to convert JSON response to Constructor object. I.e. = new Constructor( jsonResponse )

will be invoked.

Date type

var A = Nested.Model.extend({
    defaults : {
        created : Date, // = new Date()
        updated : Date.value( null ), // = null
        a : Date.value( 327943789 ), //  = new Date( 327943789 )
        b : Date.value( "2012-12-12 12:12" ) //  = new Date( "2012-12-12 12:12" )

var a = A();

a.updated = '2012-12-12 12:12';
console.assert( a.updated instanceof Date );

a.updated = '/Date(32323232323)/';
console.assert( a.updated instanceof Date );

Type spec format

To create attribute of Date type, pass Date constructor instead of default value.

time : Date or time : Date.value( x )

When default value is given, it will be converted to Date using type casting rules.

Type casting rules


Date attributes are serialized to UTC ISO date string by default. You may customize date serialization format providing attribute’s toJSON option. Following option will serialize time to milliseconds.

time : Date.has.toJSON( function( date ){ return date.getTime(); })

You can prevent attribute from being serialized, using:

time : Date.has.toJSON( false )

Date attributes are being parsed from JSON using type casting rules.

Primitive types

var A = Nested.Model.extend({
    defaults : {
        // Original backbone behaviour - no type, value is 3232
        untyped : Nested.value( 3232 )

        // defaults with primitive types are always 'typed'
        number  : 5,           // same as Number.value( 5 )
        integer : Integer.value( 6 ),
        string  : 'something', // same as String.value( 'something' )
        string1 : '',          // same as String
        boolean : true,        // same as Boolean.value( true )

        initWithNull  : String.value( null ), // Type is String, default value is null

var a = A();

a.boolean = "hello";
console.assert( a.boolean === true );

a.number = "5";
console.assert( a.number === 5 );

a.number = "hjhjfd";
console.assert( _.isNaN( a.number ) );

a.integer = 1.5423;
console.assert( a.integer === 2 );

a.string = 5;
console.assert( a.string === "5" );

a.boolean = 0;
console.assert( a.boolean === false );

Type spec format

Primitive types (Boolean, Number, String) are special in a sense that they are inferred from their values. In most cases special type annotation syntax is not really required. For example: * n : 5 is the same as n : Number.value( 5 ) * b : true is the same as b : Boolean.value( true ) * s : 'hi' is the same as s : String.value( 'hi' ) * x : null is not the same. No type will be being inferred from null value.

Integer type

NestedTypes adds global Integer type, to be used in type annotations. Integer type is not being inferred from default values, and needs to be specified explicitly.

Type casting rules


Primitives are serialized to JSON directly. You can disable serialization of particular attribute with an option:

x : Integer.value( 5 ).toJSON( false )

Untyped attributes

Type spec format

To define untyped attribute, use either of these options:

Type casting rules



When serialized, value.toJSON function will be invoked if it exists for particular value.

JSON responses are assigned to untyped attributes as is.

Models and Collections

var User = Nested.Model.extend({
    defaults : {
        name        : String,
        created     : Date,
        group       : Group,
        permissions : Permission.Collection

var a = new User(),
    b = a.deepClone();

Type spec format

To define nested model or collection, annotate attribute with Model or Collection type:

a : MyModel or b : MyModel.Collection or c : SomeCollection

Inline nested Models and Collections definitions

Inline nested definitions

var M = Nested.Model.extend({
    defaults :{
        // define model extending base Nested.Model
        nestedModel : Nested.defaults({
            a : 1,
            //define model extending specified model
            b : MyModel.defaults({
                // define collection of nested models
                items : Nested.Collection.defaults({
                    a : 1,
                    b : 2


Simple models and collections can be defined with special shortened syntax.

It’s useful in case of deeply nested JS objects, when you previously preferred plain objects and arrays in place of models and collections. Now you could easily convert them to nested types, enjoying nested changes detection and 'deep update’ features.

Type casting

Deep update example:

var user = new User();

// Following assignment... = { name: "Admin" };
// the same as this:{ name: "Admin" });

// Following assignment...
user.permissions = [{ id: 5, type: 'full' }];
// the same as this:
user.permissions.set( [{ id: 5, type: 'full' }] );

// Following assignment... = {
    nestedModel : {
        deeplyNestedModel : { attr : 'value' },
        attr : 5
// the same as this, but fire single 'change' event = 5; = 'value';

When Model or Collection attribute is assigned with the value…


Nested models and collections are serialized as nested JSON. When JSON response is received, they are being constructed or updated according to type case rules.

Change events bubbling

Event bubbling:

var M = Nested.Model.extend({
    defaults: {
        bubbleChanges : ModelOrCollection,

        dontBubble : ModelOrCollection.has.triggerWhanChanged( false )

        bubbleCustomEvents : ModelOrCollection.has
            .triggerWhanChanged( 'event1 event2 whatever' )

Change events will be bubbled from nested models and collections.

Model id references

var User = Nested.Model.extend({
    defaults : {
        name : String,
        roles : Role.Collection.subsetOf( roles ) // <- serialized as array of model ids
        location : Location.from( locations ) // <- serialized as model id

var user = new User({ id: 0 });

Server response: “{ id: 0, name : 'john’, roles : [ 1, 2, 3 ], location : 6 }”

//ref attributes behaves like normal collections and models.
assert( user.roles instanceof Collection );
assert( user.roles.first() instanceof Role );
assert( === "Boston" );

Sometimes it is suitable to serialize model references as an id or an array of ids.

NestedTypes provides special attribute data types to transparently handle this situation, as if you would work with normal nested models and collections.


Model.from represent reference to the model from existing collection, which is serialized as model id.

ref : Model.from( masterCollection )

Attribute may be assigned with model id or model itself. On `get, attribute behaves as Model type. Model id will be resolved to model on first attribute read attempt.

If master collection is empty and thus reference cannot be resolved, it will defer id resolution and get will return null. If master collection is not empty, id will be resolved to model from this collection, or null if corresponding model doesn’t exists.

Attribute counts as changed only when different model or id is assigned.


Collection.subsetOf is a collection of models taken from other 'master’ collection. On first access, it will resolve model ids to real models using master collection for lookups.

If master collection is empty and thus references cannot be resolved, it will defer id resolution and just return empty collection. If master collection is not empty, it will filter out ids of non-existent models.

Collection.subsetOf supports some additional methods:

change events won’t be bubbled from models in Collection.subsetOf. Other collection’s events will.

Master Collection

Master collection reference may be:

Attribute options


var M = Nested.Model.extend({
    defaults : {
        attr : Date.has
                .value( null )
                .toJSON( false )

Attribute options spec gives you to customize different aspects of attribute behavior, such as:

.value is an example of attribute option. In order to get access to other options you need to use keyword .has. Options specs are chainable, you can specify any sequence of options separated by dot.

.value( value )

var M = Nested.Model.extend({
    defaults : {
        a : Type.has.value( value ),
        b : Type.value( value )

Attribute’s default value. On model construction, value will be casted to Type applying usual type casting rules.

.toJSON( function( value, name ) | false )

var M = Nested.Model.extend({
    defaults : {
        a : Type.has.toJSON( function( value, name ){
            return value.text;

        b : Type.has.toJSON( false )

When attribute will be serialized as a part of model, given function will be used instead of attribute’s toJSON.

Function accepts attribute’s name and its current value, and will be executed in the context of the model, holding an attribute.

Passing false option will prevent attribute’s serialization.

.parse( function( value, name ) )

var M = Nested.Model.extend({
    defaults : {
        a : Type.has.parse( function( value ){
            return Type.factory( value );

Attribute-specific parse logic, will be executed after model’s parse method.

Function accepts attribute’s name and response value, and will be executed in the context of the model, holding an attribute.

This option is useful to parse abstract model attributes, or handle non-standard format of specific attributes.

.get( function( value, name ) )

var M = Nested.Model.extend({
    defaults : {
        a : Type.has.get( function( value, name ){
            return value;

Called during model.get( 'a' ) or model.a in the context of the model, allowing you to modify value which will be returned without altering attribute itself.

Get hook function accepts attribute’s name and its current value, and returns modified value.

Multiple get hooks are chainable, and will be applied in specified order.

.set( function( value, name ) )

var M = Nested.Model.extend({
    defaults : {
        a : Type.has.set( function( value, name ){
            return value;

Called during attribute’s update in the context of the model after type cast but before an actual set, allowing you to modify set value.

Set hook function accepts attribute’s name and value to be set, and returns modified value, or undefined to cancel attribute update.

Multiple set hooks are chainable, and will be applied in specified order.

Returned value will be casted to attribute’s type applying standard convertion rules. So, it’s guaranteed that attribute’s value will always hold the correct type.

.events( eventsMap )

var M = Nested.Model.extend({
    defaults : {
        a :{
            'isReady isNotReady' : function(){
                this.trigger( 'imwatchingyou' );

Automatically manage events subscription for nested attribute, capable of sending events. Event handlers will be called in the context of of the parent model.

.triggerWhenChanged( String | false )

var M = Nested.Model.extend({
    defaults : {
        a : ModelA.has.triggerWhenChanged( 'change myEvent' ),
        b : ModelB.has.triggerWhenChanged( false ),

Override default list of events used for nested changes detection of selected attribute.

Pass false option to disable nested changes detection for this attribute.

Nested.attribute([ optionsHash ])

var M = Nested.Model.extend({
    defaults : {
        a : Nested.attribute({
            value : null,
            toJSON : false

        b : Nested.attribute()
                .value( null )
                .toJSON( false )

Nested.attribute function returns attribute spec as it appears after .has, optionally accepting set of options as a hash.

There’s a global store for the collections, which might be useful in case of bi-directional relationships. It’s available as a member of Model (, and globally as

Initialization = {
    roles : Role.Collection,
    locations : Location.Collection

var User = Nested.Model.extend({
    defaults : {
        name : String,
        roles : Collection.subsetOf( 'store.roles' ); //
        location : Location.from( 'store.locations' }); //

Store needs to be initialized with a hash of collections and models type specs. It can be initialized several times.

Format of the spec object is the same as in Model.defaults.

Lazy loading

On first access to every member of the store, it will fetch data from the server automatically. You need to take care of update events. ‘attr1’, …)

Update all store members, which are currently loaded:

Fetches store elements with given names: 'name1', 'name2', ... )

Returns aggregate promise for xhr objects.

Nested.clear( 'attr1’, … )

Clear all store collection elements:

Clear selected store collections: 'name1', 'name2', ... )

Returns store to allow chained calls.


NestedTypes detect four error types in the runtime, which will be logged to console using console.error.

Method overriden with value

When you override function with non-function value in the subclass, it usually means an error.

This message also warn you on the situation when you made model attribute or property name the same as some base class method.

[Type Warning] Base class method overriden with value in Object.extend({ url : [object Object] }); Object = ...

Wrong model.set argument

First argument of Model.set must be either string, or literal object representing attribute hash.

Other situation means serious error. Something goes really wrong.

[Type Error] Attribute hash is not an object in Model.set( "" ); this = ...

Wrong collection.set argument

First argument of Collection.set must be either an Array, literal object, or compatible Model.

Other situation means serious error. Something goes really wrong.

[Type Error] Wrong argument type in Collection.set( "dsds" ); this = ...

Attribute has ho default value

Attempt to set an attribute which is not declared in model defaults.

[Type Error] Attribute has no default value in Model.set( "a", 0 ); this =...