When using the Backbone.js framework, model `defaults` should be a function rather than an object if it contains arrays or objects. This is because objects and arrays are passed by reference in JavaScript. So a `defaults` object that contains arrays or objects is going to set the default value of every instance to point to the same shared object or array.

Use a function instead and a fresh copy of the object or array will be peeled off for each instance.

## Noncompliant Code Example

    var Person = Backbone.Model.extend({
      defaults: {  // Noncompliant; every instance of Person will share the same instance of favoriteColors
        favoriteColors: ["blue","purple","raspberry"]
      }
    });

## Compliant Solution

    var Person = Backbone.Model.extend({
      defaults: function() {
        return {
          favoriteColors: ["blue","purple","raspberry"]
        };
      }
    });