curran / backbonecomputedproperties

An implementation of computed properties for Backbone.js

backboneComputedProperty

An small and simple implementation of computed properties for Backbone.js

Inspired by computed properties in Ember.js and dependency injection Angular.js.

Prior Art:

• Backbone mailing list thread: Backbone.Model Computed Attributes
• Blog post: Backbone.js computed properties
• GitHub: kdocki / backbone.model.computed
• GitHub: phdesign / Backbone.Spark
• GitHub Gist: tjbladez / computed.coffee

By Curran Kelleher 3/23/2014

Here's the implementation:

function addComputedProperty(model, computedProperty, dependencies, fn){
  var callFn = _.debounce(function(){
    var args = dependencies.map(function (property){
      return model.get(property);
    });
    model.set(computedProperty, fn.apply(null, args));
  });
  dependencies.forEach(function(property){
    model.on('change:' + property, callFn);
  });
}

// Example usage:
var model = new Backbone.Model({
  firstName: "Joe",
  lastName: "Schmoe"
});

addComputedProperty(model, 'fullName', 
                    ['firstName', 'lastName'],
                    function (firstName, lastName){
  return firstName + ' ' + lastName;
});

See addComputedProperty.js for a documented implementation, and example.js for a documented and more complete example.