Ember.A seems to modify array instance

[marcoow]

We're seeing a bug in the Ember Simple Auth dummy app (mainmatter/ember-simple-auth#1260) that seems to be caused by the fact that Enumerable.uniqEmber.A tries to modify the provided array. This only seems to affect addon projects where prototype extension is disabled (this is mostly an assumption for now though).

Reproduction steps:

var array = ['a', 'a'];
Object.freeze(array);
Ember.A(array);

// =>
ember.debug.js:21542 Uncaught TypeError: Cannot add property nextObject, object is not extensible
    at Object.defineProperty (ember.debug.js:21542)
    at applyMixin (ember.debug.js:20576)
    at MixinPrototype.apply (ember.debug.js:20770)
    at Object.A (ember.debug.js:37397)
    at eval (eval at init (query-string.js:35), <anonymous>:1:7)
    at Class.init (query-string.js:35)
    at new Class (ember.debug.js:36118)
    at Function._ClassMixinProps.create (ember.debug.js:36306)
    at Class.buildQueryString (oauth2-code.js:110)
    at Class.buildUrl (oauth2-code.js:120)

This only seems to fail in addon dummy apps but not in real apps.

/cc @Turbo87

[stefanpenner]

I think its Ember.A(array) that is doing the modification

[marcoow]

Hm, right - @Turbo87 and me just debugged this and we were sure it was the uniq but you're right,

var array = ['a', 'a'];
Object.freeze(array);
Ember.A(array);

actually results in the same exception. Should I update the issue above?

I assume this is still a bug though as Ember.A should also not modify the passed array?

[Serabe]

Ember.A's definition when prototypes are not to be extended applies NativeArray to the object and that defines properties on it, so I would say this is suggested behaviour.

Did this behaviour changed between versions? If you extend prototypes, is it still there?

Thank you!

[stefanpenner]

Ember.A() has no choice but to modify the array prototype, even if frozen. That is the contract it has, if it cannot it will most likely produce downstream errors.

One can think of Ember.A(y) as "casting" y as Ember.A.

[Turbo87]

@stefanpenner @Serabe It says "Does not modify the original object." in the API documentation of that function though, which is a little misleading. If it said something like "Does not modify the contents of the array" it would be more clear, but this certainly does modify the array object by adding these properties.

I never knew that Ember.A() actually changed anything, I always thought it would just create some sort of wrapper objects that has all the necessary additional properties. Sort of like a PromiseProxy I guess...

[marcoow]

One can think of Ember.A(y) as "casting" y as Ember.A.

Good to know - thanks!

I'd agree with @Turbo87 though that it might be good to update the docs. I was thinking as well that the passed object would not be touched in any way. I submitted a PR: #15032

[Serabe]

Reopening as docs issue. Thank you!