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A data binding plugin for Bacon.js.

Adds Model, Binding and Lens objects to core library to support advanced binding

Model object extends the Bacon.js Property API by providing a bidirectional binding


  • Composing Model objects using model.bind, Model.combine and model.lens
  • Attaching additional input EventStream to any Model by using model.addSource

Build Status

Model API


Creates a new model, with the given (optional) initial value.


Sets a new value for the model, also pushing this value to all two-way sources.


Returns the current value of the model. If there's no current value, returns undefined.


Modifies the value of the model by applying the given function to the current value. For instance, if the current value was 1 and you applied a multiplyBy2 function, the value would be set to 2.


Adds an input source for pushing values to the model. The source may be an EventStream or a Property. The method returns an EventStream that contains all changes from other sources than this.


Adds an input source of modification functions to the model. The source may be an EventStream or a Property, and is supposed to contain functions as values. Each of these functions are applied as modifications to the value of the model (as with using the modify method). The method returns an EventStream that contains all changes from other sources than this.


Makes a two-way binding between the two models.


Creates a new lensed model based on this one. For example:

    car = Bacon.Model({ brand: "Ford", engine: "V8" })
    engine = car.lens "engine"

Now the engine model will have the value "V8". Also, these two models are bound both ways meaning that changes in engine are reflected to car and vice versa.

See Lenses section below for full definition of Lenses.


Creates a composite model using a template. For example:

    // Model for the number of cylinders 
    cylinders = Bacon.Model(12)
    // Model for the number of doors 
    doors = Bacon.Model(2)
    // Composite model for the whole car 
    car = Bacon.Model.combine {
      price: "expensive",
      engine: { type: "gas", cylinders},

The composite model has a bidirectional binding to its components. If the cylinders model is gets a change from a UI, the car model is updated accordingly. Also, if you set the value in the car model to, say {price: "affordable", engine: { type: "electric", cylinders: 0 }, doors: 4}, the cylinders model will get a new value 0.


The model has a syncConverter function that it uses to map the incoming data values from its synchronization sources, i.e. the sources that have been added using bind, addSource, or explicitly using Model.combine. You can override this method to process the incoming values. For instance, you may convert undefined values to empty strings like this:

   model.syncConverter = function(x) { return x || "" }

Binding API

Bacon.model provides a simple Binding API for creating Model objects bound to, for instance, DOM elements. This is the API that bacon.jquery uses to create two-way bound models.


Creates a new bound Model. The options argument is an object containing the following fields:

get : zero-arg function that returns the current value from the UI

set : 1-arg function that pushes the given new value to the UI

events : an EventStream of input events from the UI. The content of these events are ignored; they are only used to trigger the polling of the new value from the UI using the get function.

initValue (optional) : initial value to be set for the model

For example, the implementation of the checkBoxValue method in bacon.jquery looks like this:

  Bacon.$.checkBoxValue = (element, initValue) ->
    Bacon.Binding {
      get: ->":checked"),
      events: element.asEventStream("change"),
      set: (value) -> element.attr "checked"value


TODO: reference to functional lenses

A lens can be defined in two ways:


Creates a lens with a p path string, such as "engine" or "engine.cylinders"

Bacon.Lens({get, set})

Creates a lens with a {get, set} pair such as { get: function(context) { .. }, set: function(context, value) { .. }}

TODO: more

Use with Node / Browserify

Bacon.model is registered in the NPM repository as bacon.model and works fine with node-browserify.

Use with Bower

Registered to the Bower registry as bacon.model.

Use with AMD / RequireJS

An example:

  paths: {
    "bacon": "components/bacon/dist/Bacon",
    "bacon.model": "../dist/bacon.model"
require(["bacon", "bacon.model"], function(Bacon) {
  var model = Bacon.Model({foo:"bar"})
  model.onValue(console, "log")
  model.set({foo: "barbaz"})

Use without AMD

Feel free to use plain old <script> tags to include Bacon and bacon.model

The prebuilt javascript file can be found in the dist directory, or here.


The bacon.model module is built using NPM and Grunt.

To build, use npm install.

Built javascript files are under the dist directory.

Automatic tests

Use the npm test to run all tests.

Tests include mocha tests under the test directory