GetIteratorFlattenable should check that iterator is an Object.

[woess]

GetIteratorFlattenable apparently is missing a check that the iterator returned by Call(method, obj) (i.e. @@iterator() or @@asyncIterator()) is an Object, as required by Iterator Record:

1. If _obj_ is not an Object, throw a *TypeError* exception.
1. Let _alreadyAsync_ be *false*.
1. Let _method_ be *undefined*.
1. If _hint_ is ~async~, then
  1. Set _method_ to ? Get(_obj_, @@asyncIterator).
  1. Set _alreadyAsync_ to *true*.
1. If IsCallable(_method_) is *false*, then
  1. Set _method_ to ? Get(_obj_, @@iterator).
  1. Set _alreadyAsync_ to *false*.
1. If IsCallable(_method_) is *false*, then
  1. Let _iterator_ be _obj_.
  1. Set _alreadyAsync_ to *true*.
1. Else,
  1. Let _iterator_ be ? Call(_method_, _obj_).
1. Let _nextMethod_ be ? GetV(_iterator_, *"next"*).
1. If IsCallable(_nextMethod_) is *false*, throw a *TypeError* exception.
1. Let _iteratorRecord_ be the Iterator Record { [[Iterator]]: _iterator_, [[NextMethod]]: _nextMethod_, [[Done]]: *false* }.
1. If _hint_ is ~async~ and _alreadyAsync_ is *false*, then
  1. Return CreateAsyncFromSyncIterator(_iteratorRecord_).
1. Return _iteratorRecord_.

[ljharb]

Wouldn’t GetV check that?

[woess]

@ljharb no, GetV performs a ToObject conversion, so if the returned iterator is an object-coercible primitive value and there's a callable next method on its corresponding prototype, GetIteratorFlattenable will not throw.

FWIW, GetIterator has a check for this case: "4. If iterator is not an Object, throw a TypeError exception."

[ljharb]

aha, thanks, good catch

[michaelficarra]

@woess Thank you for the issue. I've opened #253 to resolve it.