Existential operator (was: ||= is much needed?)

Brendan Eich brendan at mozilla.org
Tue Jun 19 11:08:57 PDT 2012

Jeremy Ashkenas wrote:
> Everywhere else in the language, `?` means existence (not null or 
> undefined) -- but when used to call a function, the check ensures that 
> the value is callable as well. In a DWIM sense, this makes sense, 
> because the only things you'd ever want to try to call in JavaScript 
> must be callable ... but I think it's strange that the meaning of 
> "existence" alters itself just for this use case. I opened a ticket 
> talking about rolling it back to "null or undefined" semantics here:
> https://github.com/jashkenas/coffee-script/issues/2315

Apart from people misreading the proposal in this issue, it does seem to 
be removing a bit of utility, but perhaps that's not actually used? Do 
CS users try to ?(-invoke a maybe-function that is sometimes neither 
null nor undefined nor typeof-type "function", but rather something that 
coerces to object?

The way to get ?( into JS is by a longer spelling:


Pretty ugly, but it puts the ? magic right where the maybe-test belongs.


More information about the es-discuss mailing list