ggaren at apple.com
Mon Nov 30 11:57:23 PST 2015
For the time being, I like “x === undefined”.
Long term, I’d like us to switch to “x === @undefined”.
We use @ to indicate reserved words in built-ins. Currently, “@undefined" does not exist, but the built-in compiler magically transforms “undefined” a safe reserved word.
The typeof and void 0 code should be fast, but I find it obtuse.
> On Nov 30, 2015, at 11:39 AM, Filip Pizlo <fpizlo at apple.com> wrote:
> I’ve also been guilty of:
> if (xxx === void 0)
> This is slightly better than saying “undefined”, since that’s not actually a reserved word.
> I believe that all of these should perform the same. We should pick one based on what looks nicest and what has the most clear semantics.
>> On Nov 30, 2015, at 11:37 AM, Darin Adler <darin at apple.com> wrote:
>> I see the following in some code:
>> if (xxx === undefined)
>> And I see the following in some other code:
>> if (typeof xxx == “undefined”)
>> if (typeof xxx === “undefined”)
>> Is one preferred over the other, style-wise? Is one more efficient than the other?
>> — Darin
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