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Use ES5 properties with Backbone. Goodbye get() and set()!


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A small Backbone plugin that lets you use ECMAScript 5 properties on your Backbone models. Instead of writing:

mymodel.set('name', 'Bob');
console.log(mymodel.get('name'));   // prints 'Bob' 

with Backprop you can write this instead (and it will have the same effect): = 'Fred';
console.log(;              // prints 'Fred' 

Backbone's get() and set() will still work if you need them. For example, you could use set() for it's {validate: true} option, although Backprop also provides a setProperties() method that accepts the same options as set() (see below).

You can install Backprop from npm with npm install backprop.


To use the plugin, add the following line to your app's initial config:


Then use Backprop.Model.extend (rather than Backbone's version) to create your models, with declarative properties in the model definition. For example:

var User = Backprop.Model.extend({
    name: Backprop.String(),
    numFollowers: Backprop.Number({ default: 0 })

Also, Backprop is CommonJS-friendly, so you can use it in Node or with client-side module systems like Browserify:

var Backprop = require('backprop');

Defining Properties

Backprop ships with a number of functions that can be used to create properties in your model definition:

  • Backprop.String => ensures the property value is a string
  • Backprop.Boolean => ensures the property value is a boolean
  • Backprop.Number => ensures the property value is a Javascript Number
  • Backprop.Integer => uses parseInt(x, 10) to ensure the value is an integer. Note that Javascript can only safely represent integers between -2^53 and 2^53.
  • Backprop.Date => calls new Date(x), passing in the assigned value as x. With these properties you can assign a Date instance, Unix timestamp (in milliseconds), or date string.
  • Backprop.Generic => Performs no type coercion (you can provide your own coerce though)

Note! Previous versions of Backprop used for defining properties. This is no longer supported– Backprop.Generic() is a drop-in replacement for these older property definitions.

Property Arguments

Each property function takes an optional hash as its only argument. The following keys are supported to pre-filter data and make dealing with properties a bit more pleasant:


Lets you specify a default value for the property. This will override anything that was set in the model's defaults hash for this attribute name. It's basically just a convenient shorthand so you can keep your default value close to the property definition.


Specify a function that transforms the property’s value before it is set. You could pass in a browser built-in like encodeURIComponent, or define your own function. If you defined your property with a type-coercing function like Backprop.String(), note that the type coercion will happen before your coerce function sees the value.

For example:

var Cat = Backprop.Model.extend({
    lives: Backprop.Number({ coerce: function(x) { return x*9; })
var c = new Cat;
c.lives = '2';
console.log(c.lives === 18)      // prints true

If true, calls a trim method on the value before setting the attribute. This is handy for removing leading/trailing whitespace from strings. For obvious reasons, you probably only want to use this with Backprop.String().

max and min

Specify values that the value must be less than/greater than (these can be used separately or together). Most useful for numbers, but will work with any values that work with < and >.

var Beer = Backprop.Model.extend({
    milliliters = Backprop.Number({ min: 330, max: 1000 })
var b = new Beer;
b.milliliters = 100;
console.log(b.milliliters);     // prints 330 
b.milliliters = 2000;
console.log(b.milliliters);     // prints 1000 

Specify an array with an enumeration of acceptable values for the property. If a value not in the array is assigned to the property, the value set to the model will be:

a) the property's current value, if one was set previously (ie. the assignment will fail)
b) the property's `default` value (if one was speficied)
c) `undefined`
var Beer = Backprop.Model.extend({
    style: Backprop.String({ choices: ['IPA', 'stout', 'ESB'], default: 'IPA' }),
    type: Backprop.String({ choices: ['on_tap', 'bottle'] })
var b = new Beer; = 'asdf';
console.log(;           // prints 'IPA' 
b.type = 'foooo';
console.log(b.type);           // prints undefined 
b.type = 'on_tap';
console.log(b.type);           // prints 'on_tap' 
b.type = 'foooo';
console.log(b.type);           // prints 'on_tap' 

The setProperties method

Backprop also adds a setProperties() method to model instances. This method accepts two positional arguments: the first is a hash of properties to set, and the second is an options object that is passed to Backbone's set() method behind the scenes. The second argument can be used to pass { validate: true } or { silent: true } for your properties, while still having the data passed through Backprop's pre-filters (eg. choices, max, min, etc).

var b = new Beer;
b.setProperties({ style: 'ESB', type: 'on_tap' }, { silent: true });

Note that if you pass any keys in setProperties()'s first hash that are not defined as properties, they will be set on the model as regular Backbone attributes.


Any browser with decent ES5 support should work fine, but IE8 and below do not fit in that category. For more complete support info see this table.

The plugin has been tested with Backbone v1.0.0, not sure if previous releases will work correctly.

Running tests

git clone git://
cd backprop
npm test


  • 0.4.0 - Removed and Backprop.monkeypatch(). Use Backprop.extendModel(Backbone.Model) instead of the latter.
  • 0.3.0 - Added property shorthands like Backprop.Number, Backprop.String, etc
  • 0.2.0 - Added Backbone.Model.prototype.setProperties()
  • 0.1.0 - Initial release


Partial inspiration came from this gist: