Existential Operator / Null Propagation Operator

Nick Krempel ndkrempel at google.com
Wed Apr 8 12:51:48 UTC 2015

The prefix `?` for an absorbing Nil value sounds good.

The semantics of `delete` may need clarifying; what should the following
construct do?

`delete ?a.b.c`

Most intuitive would be to not raise an error and return true if either the
`b` or `c` properties are missing, whether or not in strict mode. Does that
hold up?


On 7 April 2015 at 19:54, Herby Vojčík <herby at mailbox.sk> wrote:

> Kevin Smith wrote:
>> We should perhaps review this old thread:
>> https://esdiscuss.org/topic/fail-fast-object-
>> destructuring-don-t-add-more-slop-to-sloppy-mode
>> for another possible way to avoid non-compositionality.  (Look for the
>> suggestion about "Nil".  It's basically an exotic falsey object which
>> returns itself for any property lookups or calls.)
> Going a bit deeper this way, this thing (changing ref to Nil which always
> returns Nil upon call, construct and get, and getting back undefined when
> value is needed) have nicely separated concerns:
> Let's say '?foo', as an unary oper
> ator, when foo is a reference, returns Nil when foo is reference to null
> or undefined, otherwise leaves it unchanged. Then:
>  ?a.b.c just works,
>  ?d() just works,
>  new ?e[i]() just works, etc,. since ref is changed to Nil if the thing is
> null/undefined, it propagates through calls and gets, then changes itself
> to undefined value. The priority of ? must be pretty high, though, to only
> apply to nearest token.
> Plus, it can be used for "normalizing" null/undefined to undefined:
>  var normalizedFoo = ?foo;
> Seems sort of nice that it is separated and there are no special
> operations for ?., ?(, ?[.
> Herby
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