Tools for model-driven javascript applications
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What is SOJA ?

SOJA stands for Synchronized Objects in JAvascript.

The goal is to ease and make natural the development of model-driven Javascript applications.

It helps in particular to create (truly) object oriented structures, with headache-free automatic synchronization between data and their multiple representations.

SOJA is associated with several fundamental plugins:

  • UndoManager, to make snapshots of your application and to navigate between them (e.g. with Ctrl-Z)
  • BrowserState, to get a model of the browser, including window size, current url parameters (e.g. to ease navigation), ...
  • Synchronizer allows several clients or servers to ease (RESTful) patches and bidirectionnal communications. It permits e.g. to share models between several distant users, to communicate with databases, etc...
  • Animation permits to ease model animations.

The repository contains also some optional plugin to help building GUIs:

  • ModelEditor, to automatically create a form view / controler of models
  • CanvasManager to describe 2D or a 3D objects (Cam, Mesh, Image, Point...), and draw or edit them in a 2D or WebGl canvas.
  • LayoutManager to split / resize / join div elements in a dynamic way (think of a standard desktop application where a panel can be splitted, resized, ... and the proportions are maintained if the window is resized).
  • TreeView to draw / control a hierarchical tree representation.

There is also a "basic" application framework, based on the preceding tools:

  • TreeApp permits to define modular applications based with one or several canvas, a construction tree and an icon bar.

To send/receive/update shared models in realtime, SODA is a database that allows to transparently permanently save/load data and communicate with other clients (with commet or websocket).

SOJA is released under the LGPL v3 license.

How SOJA works ?

It was designed with the following principles:

  • Models can de defined recursively, and are typed (e.g. Val, Vec, Lst, Color, Layout, ConstrainedVal, ...) meaning for example that
    • you can use models to define another models (a very very basic need for Object Oriented Programming)
    • if you write myModel.myProperty.mySubProperty.set(10), views on myModel will be updated automatically in the next update round (unless if you choose to update a view only if the corresponding model(s) has direct modifications).
    • comparisons are done on values, not on references
  • Views are changed by rounds (in a lazy fashion). It means for example that
    • views are updated only once if it's not necessary to update them several times.
    • you dont have to write things like "make_silent_modification()" because you want to change several models that may cause several updates of the same view (would be a real headache for real applications)
    • you can easilly make atomic model changes (if e.g. you don't want an update until all your data are changed)
  • prototypes of basic javascript or dom objects are unmodified (meaning that you can associate Soja with any kind of other javascript library)

Starting guide

Soja is written in the great coffeescript language, so you need... to install the coffeescript compiler. To ease the compilation, you will also need working make and python installations.

After that, a make in the root directory should permit to compile the main sources, the plugins and the tests.

You can then try some tests directly using your favorite browser (e.g. by launching gen/test_ModelEditor.html), or through the Makefile (typing e.g. make test_ModelEditor)


Basic Model binding

This is an example of a basic model creation, followed by a function binding.

m = new Model a: 10, b: [ "yop", "yap" ]
bind m, -> document.body.innerHTML = "<H1>#{m.a.get()} #{m.b[0].get()}</H1>"

setTimeout ( -> m.a.set 13 ), 1000

or, in javascript:

var m = new Model({ a: 10, b: [ "yop", "yap" ] });
bind( m, function() { document.body.innerHTML = "<H1>"+ m.a.get() + " " + m.b[ 0 ].get() + "</H1>"; } );

setTimeout( function() { m.a.set( 13 ); }, 1000 );

In this example, we first create a generic Model from the anonymous object { a: 10, ... }. It recursively creates sub-models, so that m.a, m.b or m.b[1] are also models that can be observed, saved, restored, ...

The second line permits to register a function that will be called if the data of m have been changed in a preceding "round". A "round" can be defined as a contiguous set of instructions, so that in this example, the function will be called twice:

  • one time at the beginning (due to the creation of m),
  • one time and after the timeout.

Updating by rounds permits to optimize updates. As example, if the timeout function were { m.a.set( 13 ); m.b[ 0 ].set( "top" ); }, the number of function calls would be the same.

Additionnaly, values are compared to determine if models are really changed. As { m.a.set( 10 ); } would not really change the value of m.a, SOJA in this case won't call the binded function.

Model classes

It can be helpfull to create class prototypes to describe what kind of models we are dealing with (instead of using anonymous aggregates).

This example illustrates how to create a simple Color model:

class Color extends Model
    constructor: ->
            r: new ConstrainedVal( 150, { min: 0, max: 255 } )
            g: new ConstrainedVal( 100, { min: 0, max: 255 } )
            b: new ConstrainedVal( 100, { min: 0, max: 255 } )
    lum: -> 
        ( @r.get() + @g.get() + @b.get() ) / 3

or, in javascript:

var Color = ( function() {
    __extends( Color, Model );
    function Color() { this );
            r: new ConstrainedVal( 150, { min: 0, max: 255 } ),
            g: new ConstrainedVal( 100, { min: 0, max: 255 } ),
            b: new ConstrainedVal( 100, { min: 0, max: 255 } )
    Color.prototype.lum = function() {
        return ( this.r.get() + this.g.get() + this.b.get() ) / 3;
    return Color;
} )();

add_attr permit children models to know the parent ones. ConstrainedVal is basically a numeric value, with constraints like bounds, divisions, ... __extends can be found e.g. in code generated by coffeescript

Once created, this model can be binded to functions or views, as in:

c = new Color

# sliders
new_model_editor el: new_dom_element( parentNode: document.body, style: {width:300} ), model: c

# lum
l = new_dom_element parentNode: document.body
bind c, -> l.innerHTML = "Luminance = #{c.lum()}"

or, in javascript:

var c = new Color;

// sliders
new_model_editor({ el: new_dom_element({ parentNode: document.body, style: { width: 300, marginBottom: 10 } }), model: c });

// lum
var l = new_dom_element({ parentNode: document.body });
bind( c, function() { return l.innerHTML = "Luminance = " + (c.lum()); });

where we created two views of c, an instance of Color. The first view is created using the ModelEditor plugin (and consists mainly in sliders). The second is a div element (created by new_dom_element which is defined in the plugin DomHelper) that will contain the text "Luminance = #{c.lum()}", computed according to the values in c.

View classes

In most of the real cases, views are also instances of classes defined by the users.

Binding a view object means that

  • the onchange method will be called if the observed model (or a child of) has been changed during the preceding round
  • the destructor method will be called if the observed model has been destroyed.

This is an example where we create two checkboxes in document.body, synchronized with a sub-model

class MyView extends View
    constructor: ( @model, parent ) ->
        super model

        @input = new_dom_element
            parentNode: parent
            type      : "checkbox"
            nodeName  : "input"
            # onchange of the dom element
            onchange  : => @model.set @input.checked
    # surdefinition of View.onchange, called for the view creation
    onchange: ->
        @input.checked = @model.toBoolean()

m = new Model
    a: true
    b: [ "yop" ]

new MyView m.a, document.body # instance 1
new MyView m.a, document.body # instance 2

Or in javascript

var MyView = (function() {
    __extends(MyView, View);
    function MyView(model, parent) {
        this.model = model;, model);
        this.input = new_dom_element({
            parentNode: parent,
            type: "checkbox",
            nodeName: "input",
            onchange: __bind(function() {
                return this.model.set(this.input.checked);
            }, this)
    MyView.prototype.onchange = function() {
        return this.input.checked = this.model.toBoolean();
    return MyView;
var m = new Model({
    a: true,
    b: ["yop"]
new MyView(m.a, document.body);
new MyView(m.a, document.body);

new_dom_element comes from the DomHelper library.

get / set / get_state / ...


If you want to change the value of a model, you have to call the set method.

In most of the cases, set can take other models as argument, or standard javascript objects. It deeply compares the argument and stored values. If different, the stored value is changed, the model is marked as directly changed, and the parent models are marked as changed. If no new round is planned, a 1 ms timeout is created to prepare a new round.


get permits to obtain the values in standard javascript / JSON representation.

For example Val.get() will give you a number. If you make an aggregate, get() will give you a JSON representation.


JSON is a very convenient representation for objects but is limited for several reasons:

  • within JSON, objects are not typed (JSON support only basic types and anonymous aggregates)
  • JSON permits to represents trees but not graphs, e.g. in presence of cyclic references or if an object is referenced by several parents.

Due to theses limitations, Soja uses an alternative but very simple representation. For example,

m = new Model a: [ 8 ]
console.log m.get_state()

or (in javascript)

var m = new Model({ a: [ 8 ] });
console.log( m.get_state() );

will give the following text:

0 Val 8
1 Lst 0
2 Model a:1

The first column represents the model id, the second represents the type and the third is type dependant.

It permits for example to get the full state of an application, but also to get changes since a given model date (as get_state can take a model date as first parameter). The current model date is given by Model._counter.


Symmetrically, the string obtained by get_state can be used to update or construct a model, using set_state.

This procedure is used for example in the Synchronizer or the UndoManager plugins.

Some usual methods on models

equals permits to compare models with other models or objects.

toString and toBoolean permits to make some (hopefully ) conversions...

size permits to get an array representing tensorial size. For a scalar, it returns []. For an array, it returns [length], etc...

Some basic model objects

From Soja.js :

  • Model -> ancestor class, used for anonymous aggregates
  • Lst -> a list of models. It contains some usual methods for list manipulation :
    • push: ( value ) -> appends value at the end of the list
    • pop: -> remove and return the last element
    • shift: -> remove and return the first element
    • remove: ( item ) -> remove item from the list if present
    • filter: ( f ) -> return a list with items such as f( item ) is true
    • detect: ( f ) -> return the first item such as f( item ) is true. If not, return undefined
    • has: ( f ) -> return true if there is an item that checks f( item )
    • indexOf: ( v ) -> returns index of v if v is present in the list. Else, return -1
    • contains: ( v ) -> returns true if v is contained in the list
    • toggle: ( v ) -> toggle presence of v
    • splice: ( index, n = 1 ) -> remove n items starting from index
    • join: ( sep ) -> return a string with representation of items, separated by sep
  • Str -> a string
    • toggle: ( str, space = " " ) -> toggle presence of str in this
    • contains: ( str ) -> true if str is contained in this
  • Val -> a number
  • Bool -> a Boolean
    • toggle: -> self not
  • Vec -> a list of number
  • Choice -> a choice of a value inside a list
  • ConstrainedVal -> a value with potentially a miniminum, a maximum, ticks, ...
  • ...

From plugins :

  • Color (Color) -> set of constrained rgba values
  • Gradient (Color) -> color gradient
  • BrowserState (BrowserState) -> a model representing browser state (window size, current url, ...)
  • Layout (LayoutManager) -> a (dynamic) page layout description
  • Cam (CanvasManager) -> a 3D / 2D camera
  • Mesh / Point / ... (CanvasManager) -> drawable objects
  • ...

It is worth mentionning that Lst can be extended to change its basic behavior:

  • by default, length is dynamic, but it can be fixed by surdefining static_length. In this case, surdefining default_value can be usefull (e.g. for construction).
  • by default, Lst can accept any kind of model but if base_type is surdefined, one can force conversions during operations like push, set, [ n ].set, ...