Question

I’m seeing this weird behavior on Ember objects where when I alter an array that I instance.get, the changes will apply to the class default value (and consequently, to any new instance of the object).

However, if I set the alter as a computed property, it works well (since it ensures that I always send a new instance of the array).

I am wondering is this is normal behavior, it doesn’t seem to me like it should, but it’s very possible that I misunderstand a few things.

Here’s an example (available live in this jsfiddle):

A = Ember.Object.extend
  array: []

a = A.create()
a.get('array').pushObject('something') # same with push

b = A.create()
b.get('array') # ['something']


B = Ember.Object.extend
  array: ( ->
    []
  ).property()

a = B.create()
a.get('array').pushObject('something else')

b = B.create()
b.get('array') # []

Answer 1

Here is a good explanation: http://codebrief.com/2012/03/eight-ember-dot-js-gotchas-with-workarounds/ chapter 6. tl;dr: When you want to have an array as an attribute, initialize it in the constructor, something like

A = Ember.Object.extend
  array: null
  init: (->
     @_super()
     @set('array', [])
  )

updated fiddle: http://jsfiddle.net/Sly7/atjVu/4/