Tom Van Cutsem (2014-11-12T16:23:11.000Z)
d at domenic.me (2014-12-01T22:36:07.552Z)
I agree with your sentiment. I have previously advocated that Array.isArray should be transparent for proxies. My harmony-reflect shim explicitly differs from the spec on this point because people using the shim spontaneously reported this as the expected behaviour and thought it was a bug that Array.isArray didn't work transparently on proxies. As far as I can remember, the argument against making Array.isArray transparent is that it's ad hoc and doesn't generalize to other types / type tests. My opinion is that array testing is fundamental to core JS and is worth the exception.