documentcloud/underscore — comment on commit e79586515c5f635650afc32976826e01463dcd1d
File: test/objects.js line 186
By jashkenas:

As in CoffeeScript, I don't particularly care about sparse arrays and all their hangups (scary, I know). An empty array is an empty array.

That said -- we could introduce a special check to compare the non-enumerable `length` property if you like. Perhaps next to the new constructor check?