Default values are passed in by reference

[nagyv]

Having an empty array as a default value can definitely trick the user:

http://jsfiddle.net/bika/Kn5sP/2/

Is this intended?

[tbranyen]

"Remember that in JavaScript, objects are passed by reference, so if you include an object as a default value, it will be shared among all instances."

http://backbonejs.org/#Model-defaults

This is expected behavior, you can use a function for defaults and return an object that contains a reference type.

defaults: function() {
  return {
    shared: []
  };
}

[braddunbar]

Yes, this is intentional. For different behavior defaults can be provided as a function. Please see #476 for more information.

[Benjen]

I was struggling with this until I can across this issue here. Perhaps it would be beneficial to update the documentation to explain this slightly. Currently it reads:

"Remember that in JavaScript, objects are passed by reference, so if you include an object as a default value, it will be shared among all instances."

Perhaps we could change it to:

"Remember that in JavaScript, objects are passed by reference, so if you include an object as a default value, it will be shared among all instances. Defaults containing objects passed by reference should be defined using a function if you do not wish to share objects between all instances."

[braddunbar]

@Benjen That sounds reasonable to me. Care to work up a pull request to that effect?