Array subclasses and concat() ?

# Andrea Giammarchi (12 years ago)

In latest ES6 draft I can read this change:

Array.prototype.map, filter, slice, splice when used iwth array subclasses creates results arrays of the same subclass

which is good/cool/eventually/hoooray but something that has been problematic since ever in subclassing Array in JS is Array#concat, together with Array#slice and all others that returns an Array from a array-like object.

I see that slice and splice are in but reading current draft I wonder these two things:

will Array#concat produce results of the same subclass too ?
what are we suppose to expect from the classic [].slice.call(arguments) operation, an instanceof Arguments ?

Thanks for any clarification.

In latest ES6 draft I can read this change:


   - Array.prototype.map, filter, slice, splice when used iwth array
   subclasses creates results arrays of the same subclass

which is good/cool/eventually/hoooray **but** something that has been
problematic since ever in subclassing Array in JS is Array#concat, together
with Array#slice and all others that returns an Array from a _array-like_
object.

I see that slice and splice are in but reading current draft I wonder these
two things:

  1. will Array#concat produce results of the same subclass too ?
  2. what are we suppose to expect from the classic
`[].slice.call(arguments)` operation, an `instanceof Arguments` ?

Thanks for any clarification.
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