What good is the reliability of something that is more often than not useless?
Should there be a typeof hook like Symbol.hasInstance? No. `instanceof` was always sketchy due to the ability to exchange prototypes on an object. When `class` came along, it became effectively broken since `class` provides no facility for transfixing the prototype attached to an instance. On the other hand, `typeof` never had such issues. Unfortunately, when `class` came along, nothing was done to allow `typeof` to treat classes as unique types. That was disappointing. However, adding a hook means that `typeof` would lose its stability and predictability, making it essentially as useless as `instanceof`. If instead, the two changes I just mentioned were made, then `typeof` would even be able to supplant `instanceof` without losing any of its reliability. Just a thought... On Sat, Jul 27, 2019 at 3:57 PM Jordan Harband <[email protected]> wrote: > With something that while unintuitive in one case, is eternally robust and > reliable. > > If you want extensibility, define Symbol.toStringTag on your objects. > > On Sat, Jul 27, 2019 at 1:23 PM Michael Haufe <[email protected]> > wrote: > >> If it's unfixably broken[1], non-extensible, excessively vague, and >> non-orthogonal, where does that leave you? >> >> >> >> [1] <https://twitter.com/BrendanEich/status/798317702775324672> >> >> >> >> *From:* Jordan Harband <[email protected]> >> *Sent:* Saturday, July 27, 2019 3:00 PM >> *To:* Michael Haufe <[email protected]> >> *Cc:* ViliusCreator <[email protected]>; [email protected] >> *Subject:* Re: Proposal: Typeof Trap >> >> >> >> Those two PRs are about removing implementation-defined behavior from >> `typeof`, making it *more* reliable - there is no trend away from using and >> relying on `typeof`, full stop. >> >> >> >> `Symbol.hasInstance` is a part of why `instanceof` is actually unreliable >> - because user code can hook into it. It would be a massive loss imo if >> `typeof` lost its bulletproof status by adding a user hook. >> >> >> >> On Sat, Jul 27, 2019 at 12:37 PM Michael Haufe <[email protected]> >> wrote: >> >> The trend seems to be to rely on typeof less and less as time passes: >> >> >> >> From the March 2019 Agenda < >> https://github.com/tc39/agendas/blob/274e49412c09f81a0a82f386e6eead481c69adad/2019/03.md >> >: >> >> >> >> “Implementation-defined typeof still necessary?” < >> https://github.com/tc39/ecma262/issues/1440> >> >> “Normative: Remove implementation-defined typeof behavior” < >> https://github.com/tc39/ecma262/pull/1441> >> >> >> >> >> >> The only real discussion around this I can find is from a related >> proposal from Brendan Eich a few years ago: >> >> >> >> >> https://esdiscuss.org/topic/typeof-extensibility-building-on-my-value-objects-slides-from-thursday-s-tc39-meeting >> >> >> >> >> >> >> >> *From:* ViliusCreator <[email protected]> >> *Sent:* Saturday, July 27, 2019 2:04 PM >> *To:* Michael Haufe <[email protected]> >> *Subject:* RE: Proposal: Typeof Trap >> >> >> >> *Yes, but it traps `typeof `, not `instanceof`. There’s difference there.* >> >> _______________________________________________ >> es-discuss mailing list >> [email protected] >> https://mail.mozilla.org/listinfo/es-discuss >> >> _______________________________________________ > es-discuss mailing list > [email protected] > https://mail.mozilla.org/listinfo/es-discuss >
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