== Why is this an issue?

When using the Backbone.js framework with model ``++defaults++`` that contain arrays or objects, ``++defaults++`` should be defined as a function rather than an object. 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

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


=== Compliant solution

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



ifdef::env-github,rspecator-view[]

'''
== Implementation Specification
(visible only on this page)

=== Message

Make "defaults" a function.


'''
== Comments And Links
(visible only on this page)

=== on 16 Mar 2015, 07:58:33 Linda Martin wrote:
Reviewed

=== on 1 Nov 2019, 16:29:58 Elena Vilchik wrote:
https://github.com/SonarSource/SonarJS/issues/1698

endif::env-github,rspecator-view[]