[Fwd: Fail-fast on non-existing [[Get]]]

Brendan Eich brendan at mozilla.org
Wed Oct 17 11:55:18 PDT 2012

Tom Van Cutsem wrote:
> 2012/10/16 Herby Vojčík <herby at mailbox.sk <mailto:herby at mailbox.sk>>
>     I see two solutions:
>       - add something to the freeze, seal, preventExtensions family which
>     would set an object to the fail-fast [[Get]] state.
>       - use a Proxy in the proto chain to trap the unknown [[Get]] and
>     throw early
>     Do you think this needs a solution at all? If yes, which option would
>     you favour?
> The second option is easy to accomplish but pretty invasive since it 
> requires you to inherit from a particular object. If you have an 
> abstraction that already inherits from something else, you're hosed.
> Personally, I'm not convinced this is a big enough problem to warrant 
> another "mode" for Javascript objects.

This has come up in TC39, and on this list. Waldemar would like a way 
(not the default) to seal a class so typo'ed member names throw:


However, since then, I recall hearing Waldemar say that the private 
at-name syntax in classes (for him) made the case that maximally minimal 
classes hang together in ES6, without any "const class" or sealed class 

I agree it's not a big enough problem to add a "mode" or anything like 
that. Opt-in by class could be helpful. TypeScript has its optional 
member syntax (?:) and can give warnings. It seems to me this kind of 
tool-time help might be enough.


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