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

Brendan Eich brendan at mozilla.org
Sun Jun 17 22:11:06 PDT 2012

Sorry, meant to start a new thread for:


As the Syntax section hints, we can't also adopt CoffeeScript's ?( 
variant, which enables foo.bar?(args, go, here).baz and the like. The C 
syntax heritage prevails.


Brendan Eich wrote:
> David Herman wrote:
>> On Jun 15, 2012, at 5:57 PM, satyr wrote:
>>> On Sat, Jun 16, 2012 at 4:33 AM, David Herman <dherman at mozilla.com 
>>> <mailto:dherman at mozilla.com>> wrote:
>>>     As for null, I can see how there's confusion about whether to use
>>>     null vs undefined, and so I can see why CoffeeScript would just
>>>     try to blur the distinction between them.
>>> Not just for blurring. Rejecting `null` is essential for 
>>> CoffeeScript's "existence" due to `?.`, the soak/safe access operator.
>> I think you could make a case for ?. defaulting for both but ?? 
>> defaulting only undefined. The case goes something like this:
>> - The purpose of ?? is to provide a default value when no value was 
>> provided. The way to say "no value" in JavaScript is undefined.
>> - The purpose of ?. is to fail soft when doing a property lookup. 
>> Both null and undefined throw when doing a property lookup.
> Agreed. This is one choice, it's plausible because of the distinction 
> between defaulting (which requires intentional passing of a "please 
> default" sentinel value, or not passing a trailing actual argument) 
> and soaking up null-or-undefined.
> Yes, we could make ?? and ??= do the same for null as for undefined. 
> I'm not sure that's the right choice, but it's a choice. For 
> foo.bar?.baz, though, the clearer choice is to avoid throwing, which 
> means evaluating to undefined if foo.bar is missing (evaluates to 
> undefined) *or* has a value not coercible to object type (null or 
> undefined). See
> http://wiki.ecmascript.org/doku.php?id=strawman:existential_operator
> /be
> _______________________________________________
> es-discuss mailing list
> es-discuss at mozilla.org
> https://mail.mozilla.org/listinfo/es-discuss

More information about the es-discuss mailing list