On Sep 10, 2013, at 11:12 AM, Andrea Giammarchi wrote:

> As short answer, let me reformulate:
> AFAIK 99% of libraries out there believe that slice.call will return an 
> Array, no matter which realm. In ES6 I see there's too much magic involved 
> because of subclassing possibility.

Presumably this is a 100% reasonable expectation today, because that's that the 
ES<=5.1 specs say.  However, often do they depend upon the value being a direct 
instance of Array as opposed to being an instance of a subclass of an array, 
assuming that the subclass how all the observable characteristics of an Array 
instances including answering true to Array.isArray and maintaining the Array 
invariant. 

In other words, those libraries have never encountered a true subclass of 
Array.  When they do, is anything bad going to happen if the result object is 
also a subclass of Array?

BTW, I think it is useful to distinguish this use case from applying slice to 
non Array.isArray objects or using slice as a strange way to create a new Array 
instance.

Allen




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