Simple, flexible and powerful Model-View binding for Backbone.
JavaScript Ruby
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Special thanks to Derick Bailey for creating predecessor to this plugin. I've been able to reuse unit tests he created for his Backbone.ModelBinding plugin.

Backbone is a great platform for writing client side applications but I've found that as views grow in complexity, synchronizing my models and views can be a pain. I've spent the past few months trying to use existing view-model binding libraries that others were kind enough to create and share with the world. Unfortunately in the majority of my backbone application I wasn't able to leverage the existing view-model binding libraries due to various limitations.

I created a new Backbone.ModelBinder class that I have leveraged in the majority of a large client side application. The ModelBinder class helped me remove a lot of cluttered boilerplate code that existed to synchronize my models and views. Hopefully you'll find it useful too.

The Backbone.ModelBinder class:

  • Is as simple as possible yet still flexible and powerful
  • Leverages the exact same jQuery syntax that the Backbone.View event blocks use
  • Allows you to define type formatting and type conversion in your bindings
  • Provides a simple javascript only solution rather than mixing binding syntax in html templates and javascript files. I personally find mixing binding logic in my html files to be messy and confusing.

You can use this ModelBinder class to bind backbone model attributes to:
  • Read-only html elements such as <span>, <div> etc.
  • Html element attributes such as enabled, displayed, style etc.
  • Editable form elements such as <input>, <textarea> etc. This type of binding is bidirectional between the html elements and the Model's attributes.

###The ModelBinder is more efficient### It seems like many of the backbone view examples I've seen register for the model's change event and then re-render the entire view like the example shown below.
SomeView = Backbone.View.extend({
    initialize: function(){
        this.model.on('change', this.render, this);

    render: function() {
        return this;

While the style above technically works just fine it can be more efficient - especially for larger client applications that are not frequently refreshed.

If render is called multiple times, the previously created html elements are just thrown away. Converting the model to json is also an unnecessary conversion. The ModelBinder eliminates both of these inefficiencies.

## Prerequisites
  • Backbone.js v0.9.0
  • Underscore.js v1.3.1
  • jQuery v1.7.1

I've posted some [examples]( of how to use the ModelBinder but I'd recommend reading the docs first.
##Defining Binding Scope with jQuery##

One of the most powerful capabilities of the ModelBinder class is that it allows you to define scope when you create your bindings using jQuery.

  • If your views are simple (no nested Views etc.) you can rely on default scoping rules that are based off of the html name attribute.
  • If your views are more complex you can explicitly define scoping rules with jQuery selectors. Scoping will allow you to handle nested views or have the ModelBinder only manage parts of your Views and your own custom code can handle the more complicated problems.

Both scoping mechanisms will be discussed throughout the rest of this document.

##Basic ModelBinder functionality##

The ModelBinder class contains all of the logic to facilitate bi-directional view-model binding.

The ModelBinder class exposes 3 public functions shown below:

// no arguments passed to the constructor

// model is required, it is the backbone Model you're binding to
// rootEl is required, is the root html element containing the elements you want to bind to
// bindings is optional, it's discussed a bit later
bind(model, rootEl, bindings);

// unbinds the Model with the elements found under rootEl - defined when calling bind()

The `bind()` function's 3rd argument `bindings` is optional. The `bindings` arg is useful for defining binding scope and formatting and will be discussed later. If `bindings` is not defined, then `bind()` will locate all of the child elements under the rootEl that define a `name` attribute. Each of the elements with a `name` attribute will be bound to the model's attributes - the value of the element's name attribute will be used as the model's attribute name.

In the example below, the model's address attribute will be bound to the input text field with the name of 'address'. This binding is bi-directional between the view and the model.

<!-- The html -->
<input type="text" name="address"/>
<!-- The javascript -->
SomeView = Backbone.View.extend({
    render: function(){
        this.modelBinder.bind(this.model, this.el);

## Binding after elements created, rootEl ##

The bind() functions rootEl parameter should contain all of the elements that you want to bind to. Your rootEl might be the view.el property or it could be any valid html element. It does not matter if the rootEl is displayed in a browser.

The example below shows how the rootEl argument is the result of the jQuery selection "#outerDiv". This will work just like the previous example.

<!-- The html -->
<div id="outerDiv">
    <input type="text" name="address"/>
<!-- The javascript -->
SomeView = Backbone.View.extend({
    render: function(){
        this.modelBinder.bind(this.model, this.$('#outerDiv'));

## Elements are recursively bound ##

If you do not pass the bindings 3rd parameter to the bind() function, all child elements under the rootEl with a "name" attribute are bound. This includes any nested child elements that define the "name" attribute.

In the example below, the "address" and the "city" elements will be bound to the model.

<!-- The html -->
<div id="outerDiv">
    <input type="text" name="address"/>
        <div id="divTwo">
            <input type="text" name="city"/>
<!-- The javascript -->
SomeView = Backbone.View.extend({
    render: function(){
        this.modelBinder.bind(this.model, this.el);

## Binding multiple html elements to the same model attribute ##

In the example below, the <span> and the <input> elements are both bound to the model.firstName attribute. If you modified the firstName input element you would see the span automatically updated because the Model would have been updated.

<!-- The html -->
Welcome, <span name="firstName"></span>

Edit your information:
<input type="text" name="firstName"/>
<!-- The javascript -->
SomeView = Backbone.View.extend({
    render: function(){
        this.modelBinder.bind(this.model, this.el);

If your View element definitions are simple you can rely on having properly defined "name" attributes in your html elements that match your Model attribute names. Remember that **all** of the rootEl's child elements (recursive) with a "name" attribute will be bound to your Model.

If your views require formatting, conversion or more scoping due to nested or complex views you'll need to define a bindings parameter to the bind() function as discussed in the next section.

##The bindings parameter to the bind() function##

For more complicated things like formatting or defining scope for composite or nested Views you'll need to define a bindings parameter - the optional 3rd parameter to the bind() function. The bindings parameter is a javascript hash object.

The bindings hash keys are the model's attribute names and the values, in the simplest case, are jQuery selectors that must return at least 1 html element.

The example below binds model.address to the element with the id="address":

<input type='text' id='address'/>

var bindings = {address: '#address'};
modelBinder.bind(this.model, this.el, bindings);

The example below binds model.homeAddress to the element with name="homeAddress" and model.workAddress to the element with name="workAddress":

<input type="text" name="homeAddress"/>
<input type="text" name="workAddress "/>

var bindings = {homeAddress: '[name=homeAddress]', workAddress : '[name=workAddress ]'};
modelBinder.bind(this.model, this.el, bindings);

The example below binds to <input type="text" id="city"/>:

var bindings = {city: '#city'};
modelBinder.bind(this.model, this.el, bindings);

You can use any jQuery selector that you like, as long as the selector returns at least a single element. In the example below, both the <span> and the <input> elements are bound to the model.firstName attribute. In this situation, you could also eliminate the bindings and get the same behavior.

<!-- The html -->
Welcome, <span name="firstName"></span>

Edit your information:
<input type="text" name="firstName"/>
<!-- The javascript -->
var bindings = {firstName: '[name=firstName]'};
modelBinder.bind(this.model, this.el, bindings);

Here are a few more examples of the bindings hash syntax.
    Html                                            bindings entry
    <input type="text" id="firstName"/>             firstName: '#firstName'

    <input type="text" name="firstName"/>           firstName: '[name=firstName]'

    <select name="operatorSelectEl">                operator: '[name=operatorSelectEl]'
      <option value="1">Dan</option>
      <option value="2">Eli</option>
      <option value="3">Frank</option>

    <input type="radio" name="isOk" value="yes">    isOk: '[name=isOk]'

    <input type="text" class="myTestClass"          myTestAttribute: '[class~=myTestClass]'

## You can define multiple jQuery selectors ##

The binding entries can be defined as strings as shown in all previous examples but internally the string is converted to the type of entry shown below.

 firstName: {selector: '#firstName'}

The jQuery string is a hash parameter named selector. You can define arrays of selector arguments in your bindings as shown in the example below.

 firstName: [{selector: '#firstName'}, {selector: '#title'}}

In the example above, model.firstName is bound to an element with the id of "firstName" and an element with the id of "title". To define multiple selectors, just define them as an array.

The jQuery bindings leverage the jQuery delegate mechanism - which means they should be fairly efficient.


##Formatting and converting values##

The bindings can also define a converter parameter. A converter is simply a function that is called whenever a model's attribute is copied to an html element or when an html elements value is copied into a model's attribute.

Converters help you format values in your views but help keep them clean in your models.

A simple of example of using a converter to format a phone number is shown below.

var phoneConverter = function(direction, value){
  // direction is either ModelToView or ViewToModel
  // Return either a formatted value for the view or an un-formatted value for the model

var bindings = {phoneNumber: {selector: '[name=phoneNumber]', converter: phoneConverter}}
modelBinder.bind(this.model, this.el, bindings );

A converter function is passed 4 parameters.
  • Direction - either ModelToView or ViewToModel
  • Value - the model's attribute value or the view element's value
  • Attribute Name
  • Model - this is more useful when you're dealing with calculated attributes

If your binding to a read-only element like a <div> you'll just ignore the direction parameter - it's always ModelToView. In most cases, you'll be able to ignore the attribute name and model parameters but they can be helpful in some situations discussed later.

Converters can be used for simple formatting operations like phone numbers but they can also be used for more advanced situations like when you want to convert between a model and some description of the model. You might want to display a list of models in a `` element - a converter could allow you to convert between a model and a model's id making this type of binding easy to do. The example below shows how this could work. The CollectionConverter shown is defined in the ModelBinder.js file. <!-- The html --> <select name="nestedModel"> <option value="">Please Select Something</option> <% _.each(nestedModelChoices, function (modelChoice) { %> <option value="<%= %>"><%= modelChoice.description %></option> <% }); %> </select> <!-- The javascript --> SomeView = Backbone.View.extend({ render: function(){ // An example of what might be passed to the template function var nestedModelChoices = [{id: 1, description: 'This is One'}, {id: 2, description: 'This is Two'}]; $(this.el).html(this.template({nestedModelChoices: nestedModelChoices})); var binder = new Backbone.ModelBinder(); var bindingsHash = {nestedModel: { selector: '[name=nestedModel]', converter: new Backbone.ModelBinder.CollectionConverter(nestedModelChoices).convert} }; binder.bind(this.model, this.el, bindingsHash); ## Converters can display calculated attributes ## Sometimes your models will have computed attributes. You could cache computed values inside a model's attribute collection and it would be bound like any other attribute. I favor this solution but it's not perfect because when you save models back to the server, the calculated attributes are sent. If your model's computed attribute is calculated via a function we can use a converter for the binding. In the example below, we have a simple computed attribute named hoursLeft calculated by the function calculateHoursLeft(). SomeModel = Backbone.Model.extend({ defaults: {currentHours: 3, totalHours: 8}, calculateHoursLeft: function(){ return this.get('totalHours') - this.get('currentHours'); } }) // Here is how how we could create a binding for a calculated attribute var bindings = {currentHours: {selector: '[name=hoursLeft]', converter: this.model.calculateHoursLeft}}; modelBinder.bind(this.model, this.el, bindings); In the example above, we are binding to the model's attribute 'currentHours' because when currentHours changes the hoursLeft calculated value will change - the converter will be invoked at that time. The converter is simply the model's calculateHoursLeft() function. The function just ignores the parameters passed to it and calculates the hours left. If the currentHours attribute is also bound to another html element you could specify an array of element bindings in the binding definition like the example shown below. var bindings = {currentHours: [ {selector: '[name=hoursLeft]', converter: this.model.calculateHoursLeft}, {selector: '[name=currentHours]']}; modelBinder.bind(this.model, this.el, bindings); If converters need any other special logic they can be defined in another function outside of the Model because the converter function is passed the Model as a parameter. ##Binding to html element attributes## You can also define bindings to be bound to any html element's attribute like enabled, class, style or any other attribute you define. The example below shows how to use the elAttribute option. In this example, the address element will be enabled depending on what the Model.isAddressEnabled attribute is. var bindings = {isAddressEnabled: {selector: '[name=address]', elAttribute: 'enabled'}}; modelBinder.bind(this.model, this.el, bindings); You could also extend the example above to be a bit more complicated. Let's pretend the Model has an attribute called customerType and if customerType == 'residential' we want the address to enabled, otherwise we want it disabled. We can handle this type of binding by leveraging both `converter` and `elAttribute`. The example below shows how this would work. When the Model.customerType is updated, the address input element's enabled attribute would be updated. var addressEnabledConverter = function(direction, value) { return value === 'residential'; }; var bindings = {customerType: {selector: '[name=address]', elAttribute: 'enabled', converter: addressEnabledConverter}}; modelBinder.bind(this.model, this.el, bindings); You could also bind to an element's class property as shown in the example below. <!-- The html --> <div id="patientPic" class="patientPic"></div> <!-- The javascript --> var bindings = {gender: {selector: '#patientPicture', elAttribute: 'class'}}; modelBinder.bind(this.model, this.el, bindings); In this example, the model.gender value is either "M" or "F". The CSS files define styles for "patientPic" with either "M" or "F" to show the correct type of avatar. ##Proper scope helps you bind to complex nested views## Sometimes you'll have nested models displayed in nested views. An example of a nested backbone model is shown below. The personModel has a nested homeAddressModel. var personModel = new Backbone.Model({firstName: 'Herman', lastName: 'Munster'}); var homeAddressModel = new Backbone.Model({street: '1313 Mockingbird Lane', city: 'Mockingbird Heights'}); personModel.set({homeAddress: homeAddressModel}); In the example above, the nested model is also a backbone.Model but sometimes your nested models are raw javascript objects. I'll talk about that situation a bit later. You can bind to this type of nested backbone model fairly easily with the ModelBinder. There are 2 basic ways to bind nested Models in a View: With a scoped rootEl that only contains html elements specific to the nested Model. With scoped bindings selectors in the bindings hash. ##Nested View option 1: A scoped `rootEl`## If your nested view can be defined under a single parent element such as a <div> you can pass that parent element as the rootEl for your nested ModelBinder as shown in the example below. It refers to the personModel and homeAddressModels defined in a previous code snippet. <!-- html --> <div id="personFields"> <input type="text" name="firstName"/> <input type="text" name="lastName"/> </div> <div id="homeAddressFields"> <input type="text" name="street"/> <input type="text" name="city"/> </div> <!-- javascript --> personBinder.bind(this.personModel, this.$('#personFields')); addressBinder.bind(this.personModel.get('homeAddress'), this.$('#homeAddressFields')); In the example above, the nested homeAddressModel is bound to the correct fields because they are scoped by a single parent element. The personModel bindings also needed to be separately scoped as well. If the personModel fields were defined on a level that also included the homeAddressFields then the homeAddressFields would have appeared in the personModel. The next option shows how to avoid that situation. ##Nested View option 2: scoped bindings## If your parent and nested Model html elements cannot live under their own parent elements then you'll need to define the bindings with jQuery selectors that are properly scoped as shown in the example below. <!-- Html --> <input type="text" name="firstName"/> <input type="text" name="lastName"/> <input type="text" name="street"/> <input type="text" name="city"/> <!-- javascript --> var personBindings = {firstName: '[name=firstName]', lastName: '[name=lastName]'}; personBinder.bind(this.personModel, this.el, personBindings); var addressBindings = {street: '[name=street]', city: '[name=city]'}; addressBinder.bind(this.personModel.get('homeAddress'), this.el, addressBindings); ##The ModelBinder can be a partial solution## In some situations, you might have very complex views where you only want some of your view's elements bound by the ModelBinder. To limit the scope of which fields are bound, you just need to properly scope your bindings hash. In the example below, the modelBinder will ignore the "phone" and "fax" elements. <!-- Html --> <input type="text" name="firstName"/> <input type="text" name="lastName"/> <input type="text" name="phone"/> <input type="text" name="fax"/> <!-- javascript --> var personBindings = {firstName: '[name=firstName]', lastName: '[name=lastName]'}; modelBinder.bind(this.personModel, this.el, personBindings); ##Quickly create and modify bindings## In some situations, you might have a large amount of elements that need to be bound but only a few of them need a converter or elAttribute defined. You probably don't want to define all of the element bindings manually just to add a converter to a few of them. The utility function Backbone.ModelBinder.createDefaultBindings can help you in this situation. The Backbone.ModelBinder.createDefaultBindings( ) is shown below. // A static helper function to create a default set of bindings that you can customize before calling the bind() function // rootEl - where to find all of the bound elements // attributeType - probably 'name' or 'id' in most cases // converter(optional) - the default converter you want applied to all your bindings // elAttribute(optional) - the default elAttribute you want applied to all your bindings Backbone.ModelBinder.createDefaultBindings = function(rootEl, attributeType, converter, elAttribute){ ... } You can use this function to gather all of the elements under the rootEl with a "name" or "id" attribute and quickly create all of the bindings and then modify those bindings. You might want to delete one or more of the bindings, add converters or elAttributes to bindings etc. Be careful when you use this with radio buttons - you might not get the proper selectors if your not careful. An example of how you might use createDefaultBindings( ) is shown below. // The view has several form element with a name attribute that should be bound // but one binding requires a converter and one of the bindings should be removed var bindings = Backbone.ModelBinder.createDefaultBindings(this.el, 'name'); bindings['phone'].converter = this._phoneConverterFunction; delete bindings['complicatedAttribute']; this._modelBinder.bind(this.model, this.el, bindings); The Power of jQuery Your jQuery selectors can be based off of a class attribute or anything else you'd like as shown in the example below. <!-- html --> <input type="text" class="partOne" name="address"/> <input type="text" class="partOne" name="phone"/> <input type="text" class="partOne" name="fax"/> <!-- javascript --> SomeView = Backbone.View.extend({ render: function(){ $(this.el).html(this.template({model: this.model.toJSON()})); var bindingsHash = {isPartOneEnabled: {selector: '[class~=partOne]', elAttribute: 'enabled'}}; this.modelBinder.bind(this.model, this.el, bindingsHash); } In this example, all 3 html elements enabled attribute are bound to the Model's isPartOneEnabled attribute. This is because the jQuery selector '[class~=partOne]' returned all 3 elements. Calling bind() multiple times Calling ModelBinder.bind() will automatically internally call the unbind() function to unbind the previous model. You can reuse the same ModelBinder instance with multiple models or even rootEls - just be aware that all previous bindings will be removed. ## Model values are copied to views when bind() is called ## The model's attributes are bound are copied from the model to bound elements when the bind() function is called. View element default values are not copied to the model when bind() is called. That type of behavior belongs in the Backbone.Model defaults block. ## Cleaning up with unbind() ## When your views are closed you should always call the unbind() function. The unbind() function will un-register from the model's change events and the view's jQuery change delegate. If you don't call unbind() you might end up with zombie views and ModelBinders. This is particularly important for large client side applications that are not frequently refreshed. ## The '.' syntax for nested models ## The ModelBinder doesn't directly support '.' to reference nested Models when binding. If you have a Backbone.Model implementation that is able to support the '.' syntax for nested models you'll be able to use the ModelBinder. I've done a bit of testing with the backbone-deep-model and it seems to work well with the ModelBinder. Here is a simple example showing how to use backbone-deep-model with the ModelBinder. The nested models are just plain javascript objects with the deep-model plugin. If your nested objects are Backbone.Models you'll need something similar to the deep-model plugin. ## AMD / Require.js support AMD / Require.js support was added in version 0.1.4 Release Notes / Versions v 0.1.4 May 11, 2012 AMD / Require.js support added Initial version of the CollectionViewBinder added v 0.1.3 May 9, 2012 Started properly tagging my versions :) v 0.1.2 Added the {source: 'ModelBinder'} option to the model.set call - allows you to know the source of a model's change event Bug fix - when binding the elAttribute to class I wasn't going through the converter function v 0.1.1 An empty selector string will now bind to the rootEl Removed elementBinding.isSetting guard which was unnecessary and short circuited updating multiple bound elements with the same name v 0.1.0 Initial version starting April 16th. Future api changes will have updated version numbers. Legal Info (MIT License) Copyright (c) 2012 Bart Wood Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions: The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software. THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.