[colin_jack]

This is from the a section on custom iterators in the related blog post (https://brendaneich.com/2012/10/harmony-of-dreams-come-true/):

"We require opt-in to avoid future-hostility against custom iterators for collection objects. Such objects probably do not want any kind of general property iterator default, which if left on Object.prototype, might be object-detected and prevent installation of the correct custom iterator factory."

I can see the sense in that but I find all the little caveats in JS are one of it's weaknesses which makes me dislike this idea. Am I wrong to think they should have just put in a default iterator but made it easy to spot it so that you could replace it with a custom iterator where appropriate?

[BrendanEich]

Python does not have a default iterator for its objects. It does for dicts of course, but JS objects are not dicts (lots of issues there).

[colin_jack]

I would just think default iterators are a sensible default especially for maps and that getting them in would be worth the very slight pain it might cause people wanting to attach custom iterators.

[BrendanEich]

Maps have a default iterator as shown in my slides. Sets too.

Best to take this to es-discuss. For now, we're sticking with Python, which did not give its top-class (non-dict) Object a default iterator.